Test
MODULE 3
Este test tiene tipos de pregunta que se abren en el reproductor de siempre.
Preguntas del test (47)
1The modern periodic table is based on the one published by [blank_start]Mendeleev[blank_end] in 1869. His table should the elements in order by [blank_start]weights[blank_end]. Elements with similar properties were arranged in [blank_start]vertical[blank_end] columns. Gaps were left where no elements fit in, and properties were [blank_start]predicted[blank_end]. These predicted elements [blank_start]have[blank_end] been found. The order of elements were rearranged where their properties didn't fit. The arrangement of the elements or groups of elements, in order of their weights corresponded to their valencies and [blank_start]chemical[blank_end] properties.
- Aweights
- Batomic number
- Cvertical
- Dhorizontal
- Epredicted
- Fknown
- Ghave
- Hhaven't
- IMendeleev
- JNewlands
- Kchemical
- Lmolecular
2Horizontal row is a group. A column is a period and they are ordered in chemical and physical properties.
- AVerdadero
- BFalso
3Which are true?
- APeriodicity is the trend in properties that is repeated across each period.
- BUsing periodicity, prediction can be made about the likely properties of an element and its compounds.
- CTrends down a group affect periodic trends.
- DAcross period, elements change from non metals to metals. As you move down, this change moves further to the right.
- EElements in a period have atoms with the same number of electrons in their outer shells – this explains their similar chemical behaviour. This repeating pattern of similarity is caused by the repeating patters of electron configuration.
4The higher the value of the quantum number, n, the higher the energy level and the further the shell is from the nucleus. True or false?
- AVerdadero
- BFalso
5A mixture of ions is called?
- AIon Mass
- BPlasma
- CIonic Force
6The energy needed to form positive ions is known as the [blank_start]ionization energy[blank_end]. The first ionization energy is a measure of how easily an atom [blank_start]loses[blank_end] an electron to form a [blank_start]1+ ions[blank_end].
The energy is supplied to overcome the attraction between the [blank_start]electron[blank_end] and proton.
The nuclear attraction experienced by an electron depends on three factors: [blank_start]Atomic[blank_end] radius, nuclear charge and electron [blank_start]shielding[blank_end] or screening.
ATOMIC RADIUS: The larger the radius, the [blank_start]smaller[blank_end] the nuclear attraction experienced by the outer shell.
NUCLEAR CHARGE: The higher the nuclear charge, the [blank_start]larger[blank_end] the attractive force.
SHIELDING: Inner shells of electrons repel the outer electrons as they are all [blank_start]negative[blank_end]. [blank_start]More[blank_end] inner shells, the larger the effect is as the nuclear attraction is smaller.
[blank_start]Successive[blank_end] ionization energies are a measure of the amount of energy needed to remove electrons.
Each is [blank_start]higher[blank_end] than the one before as there is [blank_start]less[blank_end] repulsion between the remaining electrons and they will be drawn closer in. The nuclear charge will [blank_start]outweigh[blank_end] the negative charge every time an electron is removed.`- Aionization energy
- Bloses
- C1+ ions
- Delectron
- Eneutron
- FAtomic
- Gshielding
- Hsmaller
- Ilarger
- Jnegative
- Kpositive
- LMore
- MSuccessive
- Nhigher
- Oless
- Poutweigh
7You will notice that the ionization energy of the noble gas is the highest. Why is this?
- AThese atoms have a full outer shell of electrons and a high positive attraction from the nucleus, so energy values are higher.
- BJust coincidence.
- CBecause they have larger shells, therefore are heavier and need more energy.
8Across a period, ionization energy [blank_start]increases[blank_end]. This is as the number of protons increases, so there is a higher attraction on the [blank_start]electrons[blank_end]. They are added to the same shell, so its drawn [blank_start]closer[blank_end] (electron shielding doesn't change).
This results in attraction between the nucleus and outer electrons increases, needing more energy to remove.
There is a small [blank_start]decrease[blank_end] in the first ionization energy between the group 2 and 13 elements. This is as the group 13 elements have their outermost electron in a p-orbital, whereas group 2 have them in their 2 level. P orbitals have a slight [blank_start]higher[blank_end] energy than s and so are marginally further away from the nucleus. This means that electrons are slightly easier to remove.
A similar decrease occurs between group 15 and 16. As you move group group 13 to 18, outer electrons are found in p orbitals.
In group 13, 14 and 15 each of the p orbitals contains only a single electron. In group 16, however, the
outermost [blank_start]electron[blank_end] is now spin-paired in the p orbital.
Electrons that are spin-paired experience some [blank_start]repulsion[blank_end] – this makes the first outer electron slightly easier to remove, so a slightly lower first ionization energy is observed.
There is also a decrease in atomic radius moving across a period, because the increase nuclear charge pulls the electrons towards it.
There is sharp decrease in first ionization energy between the end of one period and the start of the next. This is due to the addition of a new [blank_start]shell[blank_end], which is further from the nucleus, which leads to an increase from the nucleus, and more [blank_start]shielding[blank_end].
Moving down a group, ionization energies [blank_start]decrease[blank_end]. This is as distance from the nucleus decreases and there is more shielding. The number of protons in the nucleus also increases moving down the a group, but is [blank_start]outweighed[blank_end] by the distance and shielding.
Taking all of these into account, the attraction between the nucleus and the outer electrons decreases down a group, and so does [blank_start]ionization[blank_end] energies.- Aincreases
- Belectrons
- Ccloser
- Ddecrease
- Ehigher
- Felectron
- Grepulsion
- Hshell
- Ishielding
- Jdecrease
- Koutweighed
- Lionization
9In Metallic bonding, the atoms are ionised. Positive ions occupy fixed positions in a lattice. The outer shell electrons are delocalized, they are shared between all the atoms. The metal is held by the attractions between the anions and electrons. True or false?
- AVerdadero
- BFalso
10Giant metallic lattices have unique properties:
- [blank_start]HIGH[blank_end] MELTING/BOILING POINT: The attraction between the [blank_start]cations[blank_end] and electrons is strong, so a high [blank_start]temperature[blank_end] is needed to overcome the metallic bonds.
- [blank_start]GOOD[blank_end] ELECTRICAL CONDUCTIVITY: The [blank_start]free[blank_end] moving electrons can carry electricity.
- MALLEABILITY DUCTILITY: They are ductile, which means they [blank_start]can[blank_end] be stretched into wires. They are malleable too. This is due to the electrons being able to move, which gives the structure a degree of give, which allows layers to [blank_start]slide[blank_end].- AHIGH
- BLOW
- Ccations
- Danions
- Etemperature
- Felectron shielding
- GGOOD
- HBAD
- Ifree
- Jnon
- Kcan
- Lcannot
- Mslide
- Nstick
11The melting points of elements change moving across periods 2 and 3. These tell us about the structures of the elements.
Between group 1 and 14, melting points [blank_start]increase[blank_end] steadily. This is as the elements have giant structures. For each successive group, if an element has a giant metallic lattice, the nuclear charge increases and so does the number of electrons in the [blank_start]outer[blank_end] shell causing a stronger attraction. If its covalent, each group has more [blank_start]electrons[blank_end] to form covalent bonds with.
Between group 14 and group 15, there is a sharp [blank_start]decrease[blank_end] in melting point. This is because the elements have simple molecular structures – each molecule is attracted to others by relatively weak [blank_start]intermolecular[blank_end] froes.
Between group 15 and group 18, the melting points remain [blank_start]low[blank_end] - the elements have [blank_start]simple[blank_end] molecular structures.
Many forms of [blank_start]carbon[blank_end] and silicon create giant covalent bonding, giving them [blank_start]high[blank_end] melting points. Diamond forms a lattice where each carbon atoms forms [blank_start]four[blank_end] other carbon atoms around it.
Graphene forms a two dimensional giant lattice, [blank_start]one[blank_end] carbon atom thick, of interlocking hexagonal carbon rings. Its strong, [blank_start]light[blank_end] and conducts electricity. It has uses in [blank_start]nanotechnology[blank_end].- Aincrease
- Bouter
- Celectrons
- Ddecrease
- Eintermolecular
- Flow
- Gsimple
- Hcarbon
- Ihigh
- Jfour
- Kone
- Llight
- Mnanotechnology
12All 5 elements in group 2 have hydroxides that are alkaline, which is reflected in the common name for this group – alkaline earth metals. They have a tendency to lose 2 electrons. The reactivity of the elements increases moving down the group, Be is the least, B is the most. Is this true or false?
- AVerdadero
- BFalso
13They all have similar properties: reasonably [blank_start]high[blank_end] melting and boiling points, are light metals with low densities, and form colorless [blank_start]white[blank_end] compounds.
They have their highest-energy electrons in an [blank_start]s[blank_end] sub-shell, with 2 more electrons than the noble gases (outer shell has 2). They need to lose 2 electron to achieve noble gas [blank_start]configuration[blank_end].
The ionization energy values for the elements show that these two outer electrons are lost more easily going down the group to [blank_start]barium[blank_end]. This means reactivity increases going down the group. Its due to larger atomic [blank_start]radius[blank_end]+[blank_start]shielding[blank_end].- Ahigh
- Bwhite
- Cs
- Dconfiguration
- Ebarium
- Fradius
- Gshielding
14The group 2 metals are reactive metals and strong reducing agents. They are oxidized in their reactions to form 2+ ions. They react vigorously with oxygen – a redox reaction. The production is an ionic oxide with the general formula MO. All of the group 2 elements, except one react with water to form hydroxides with the general formula x(OH)2. Hydrogen gas is also formed. Mg reacts with water very slowly, and moving further down, the reaction quickens up. Which one element in group 2 DOESNT react with water?
- ABoron
- BBeryllium
- CCalcium
15Group 2 oxides react with water to form what?
- AMetal Hydroxides
- BMetal Solutions
- CMetal Oxides
16 The metal hydroxides are soluble in water, and form alkaline solutions with water as they release OH- ions. The pH is usually around 10 and 12. When a hydroxide is more soluble than another, it releases more OH- ions, making more alkaline solution with a higher pH. Which of these are true?
- ABe is insoluble in water.
- BMagnesium forms Mg(OH)2 which is slight soluble in water.
- CBa(OH)2 is more soluble, which a higher OH- concentration.
- DCalcium is insoluble.
17The oxides, carbonates and hydroxides of group 2 metals are [blank_start]basic[blank_end] – react with acids to form a salt and water: MgO(s)+2HCl(aq)MgCl2(aq)+H2O(l)
As these reactions with [blank_start]hydrochloric[blank_end] acid taken place, you will see a solid oxide or hydroxide [blank_start]dissolve[blank_end]. The alkalinity of group 2 metal compounds mean they have many purposes.
NEUTRALISING ACIDIC SOILS:
Calcium hydroxide, Ca(OH)2 is used by farmers and gardeners as ‘[blank_start]lime[blank_end]’ and it is used to reduce the [blank_start]acidity[blank_end] levels of soil.
INDIGESTION REMEDIES:
Human stomachs contain a small amount of hydrochloric acid. When we suffer from indigestion, there is a build up of too much of this acid. Many remedies are available, e.g. [blank_start]Milk[blank_end] of Magnesia, which contains magnesium hydroxide Mg(OH)2. This neutralizes the [blank_start]excess[blank_end] acid producing a salt and water:
Mg(OH)2 + 2HCl MgCl2 + 2H2O
BUILDING AND CONSTRUCTION USES:
Calcium carbonate (CaCO3) is a building material present in [blank_start]limestone[blank_end] and marble. It is also used in the manufacture of [blank_start]glass[blank_end] also. However they react with acids:
CaCO3 + 2HCl CaCl2 + H2O + CO2
Most rainwater has a acidic pH, which leads to a gradual [blank_start]erosion[blank_end] of objects made using limestone or marble such as [blank_start]building[blank_end] or statues.- Abasic
- Bhydrochloric
- Cdissolve
- Dlime
- Eacidity
- FMilk
- Gexcess
- Hlimestone
- Iglass
- Jerosion
- Kbuilding
18The group 7 elements, are F, Cl, Br, I and At. They have low melting and boiling points, and exist as diatomic molecules. They have 7 outer electrons, 5 being in the p sub-shell. The halogens are very reactive and highly electronegative. They are good at attracting electrons, meaning they are good oxidizing agents. Their ions are halides, which are 1- ions. True and False?
- AVerdadero
- BFalso
19The reactivity and oxidizing power of the halogens decrease moving down the group because:
- The atomic radius [blank_start]increases[blank_end]
- Electron [blank_start]shielding[blank_end] increases
- The ability to gain an electron in the p sub-shell and form 1- ions [blank_start]decreases[blank_end].
This decrease in reactivity can be shown in the reactions that halogens undergo with other halide ions. Redox reactions occurs between [blank_start]aqueous[blank_end] solutions of halide ions – Cl-, Br- and I- and aqueous solutions of [blank_start]halogens[blank_end] – Cl2, Br2 and I2.
A more reactive halogen will oxidize and displace a halide of a less reactive halogen – a [blank_start]displacement[blank_end] reaction.
Halogens form different colored solutions, so color changes indicate redox reactions have occurred. The mixture is usually shaken with an [blank_start]organic[blank_end] solvent, such as cyclohexane (distinguish between [blank_start]bromine[blank_end] and iodine).
Chlorine oxidizes both Br- and I- ions.
Cl2 + 2Br 2Cl- + Br2 [blank_start]ORANGE[blank_end] IN WATER +CYCLOHEXANE
Cl2 + 2I 2Cl- + I2 BROWN IN WATER, [blank_start]VIOLET[blank_end] IN CYCLOHEXANE
Bromine can only oxidize I- ions.
Br2 + 2I- 2Br- + I2 BROWN IN WATER, VIOLET IN CYCLOHEXANE
Iodine doesn't oxidize either Cl- and Br- ions.
Disproportionation is a reaction in which the same element is both [blank_start]reduced[blank_end] and oxidized.- Aincreases
- Bshielding
- Cdecreases
- Daqueous
- Ehalogens
- Fdisplacement
- Gorganic
- Hbromine
- IORANGE
- JVIOLET
- Kreduced
20Chlorine kills bacteria, making water safe to drink. Chlorine reacts with water forming HCl and Chloric (I) acid, HClO. Chlorine is both reduced and oxidized.
- AVerdadero
- BFalso
21How do you test for carbonate ions?
- AReacting with acid, and bubbling gas through lime water.
- BAdd dilute HCl and BaCL2.
22How do you test for sulphate ions?
- AAdd dilute HCl and BaCl2.
- BAdd sodium hydroxide solution to the compound and heat gently. Test with red litmus paper.
23How do you test for halides?
- ADissolve in water, and add aqueous silver nitrate. Note colour, and if its hard to distinguish, add aqueous ammonia (dilute first). Note solubility.
- BAdd sodium hydroxide solution to the compound and heat gently. Test with red litmus paper.
24How do you test for ammonium ions?
- AAdd sodium hydroxide solution to the compound and heat gently. Test with red litmus paper.
- BAdd in dilute halide ions.
25Energy is a type of what energy that lies within chemical bonds.
- APotential energy
- BChemical energy
- CKinetic energy
26Enthalpy, H, is the [blank_start]thermal[blank_end] energy that is stored in a chemical system. You cant measure directly the enthalpy of reactions or products, but measure the energy [blank_start]absorbed[blank_end] or [blank_start]released[blank_end] to the surroundings during chemical change.
Thermal energy is used as they can be monitored using [blank_start]temperature[blank_end] changes.
The system us the actual [blank_start]chemical[blank_end] reaction (atoms and bonds involved), and the [blank_start]surroundings[blank_end] is everything else.
If thermal energy is released, the amount that leaves is the same as the amount that goes into the surroundings. Conservation of energy means:
- heat loss in a chemical system = heat [blank_start]gain[blank_end] to the surroundings (temp [blank_start]incr[blank_end].)
- heat gain in a chemical system = heat [blank_start]loss[blank_end] from the surroundings. (temp [blank_start]decr[blank_end].)
In some reactions, the produces have more/less chemical energy than the reactants.
An enthalpy change, is:
- [blank_start]heat[blank_end] exchange with the surrounding, during a chemical reaction, at [blank_start]constant[blank_end] pressure.
- the difference between the enthalpy of the [blank_start]products[blank_end] and the enthalpy of the [blank_start]reactants[blank_end]- Athermal
- Babsorbed
- Creleased
- Dtemperature
- Echemical
- Fsurroundings
- Ggain
- Hincr
- Idecr
- Jloss
- Kheat
- Lconstant
- Mproducts
- Nreactants
27Which is correct for exothermic reactions?
- AThe enthalpy of the products is smaller than of the reactants.
- BThere is a heat loss from the chemical system to the surroundings.
- CEnthalpy change is a negative sign because heat has been lost by the chemical system.
- DThe enthalpy of the products is greater than the enthalpy of the reactants.
- EThere is a heat gain to the chemical system from the surroundings.
28Which are correct for endothermic reactions?
- AThe enthalpy of the products is greater than the enthalpy of the reactants.
- BThere is a heat gain to the chemical system from the surroundings.
- CEnthalpy change has a positive sign because heat has been gained by the chemical system.
- DEnthalpy change is a negative sign because heat has been lost by the chemical system.
- EThere is a heat loss from the chemical system to the surroundings.
29In enthalpy profile diagrams, in exothermic reactions the change is negative, and endothermic the change is positive. Is this true or false?
- AVerdadero
- BFalso
30Even though the products have a lower energy than the reactants, there still has to be an input of energy to break the first bond and start the reaction. Its often supplied by a spark or by heating the chemicals (e.g. spark for gas) This happens in exothermic reactions. In an endothermic reaction, there is a _________ activation energy.
- AHigher
- BLower
31Thermodynamics is a branch of physical chemistry that focuses on [blank_start]energy[blank_end] in a chemical system, which is the reactants and the products. Energy is conserved; it cannot be created or destroyed.
For chemists to carry out meaningful calculations, all values must be measured under an agreed set of conditions. These are standard conditions:
- [blank_start]100[blank_end]kPa – this is [blank_start]100,000[blank_end] Pa
- [blank_start]298[blank_end]K – which is [blank_start]25[blank_end] degrees.
All substances are in their [blank_start]standard[blank_end] states, i.e the most stable form. For example, carbon would be graphite rather than diamond. (standard= plimsoll line)
Enthalpy change of reaction is the energy associated with a given reaction.
Enthalpy change of [blank_start]formation[blank_end] is the energy change that takes place when [blank_start]1[blank_end] mole of a compound is formed from its constituent elements in their standard state under standard conditions. (Can have fractions in the equation). Its in 0kJmol-1.
Enthalpy change of combustion is the energy change that takes place when 1 mole of a substance is [blank_start]completely[blank_end] combusted.
Enthalpy change of [blank_start]neutralization[blank_end] is the energy change associated with the formation of 1 mole of water from a neutralization reaction.- Aenergy
- B100
- C100,000
- D298
- E25
- Fstandard
- Gformation
- H1
- Icompletely
- Jneutralization
32You cannot measure enthalpy directly but measure enthalpy change. The temperature of a chemical system is monitored. Calorimetry uses a mathematical relationship to calculate enthalpy change from experimental quantitative data. What is this calculation?
- AQ=mC(tempchange)
- Btempchange=QmC
- Cm=tempchangeCQ
33Energy is needed to break a chemical bond and the [blank_start]same[blank_end] amount of
energy is released when the same bond is made.
Energy is needed to [blank_start]break[blank_end] bonds (endothermic) and when bonds form, the same quantity of energy is [blank_start]released[blank_end] (exothermic).
A chemical reaction is a 3 step process:
- [blank_start]Reactant[blank_end] bonds are broken, which takes in energy =[blank_start]endothermic[blank_end].
- Atoms arrange to form products.
- Product bonds are [blank_start]formed[blank_end]. This released energy = [blank_start]exothermic[blank_end] change.
In endothermic reactions, [blank_start]more[blank_end] energy is needed to break the reactant bonds than is released when the product bonds are made, [blank_start]taking in[blank_end] energy.
In exothermic reactions, more energy is released when product bonds are [blank_start]formed[blank_end] than is needed to [blank_start]break[blank_end] reactant bonds, releasing energy.- Asame
- Bopposite
- Cbreak
- Dmake
- Ereleased
- Ftaken in
- GReactant
- HProduct
- Iformed
- Jbroken
- Kendothermic
- Lexothermic
- Mexothermic
- Nendothermic
- Omore
- Pless
- Qtaking in
- Rgiving out
- Sformed
- Tbroken
- Ubreak
- Vmake
34Hess’ law states that the enthalpy change in a chemical reaction is dependent of the route it takes.
- AVerdadero
- BFalso
35The rate of reaction is defined as the change in concentration of a reactant or a product in a given time. How would you this out?
- Arate= change in concentration/time
- Brate= time/change in concentration
- Crate= 1- concentration/time
36Usually concentrations of reactants are highest at the start of a reaction when the rate it at its fastest. The rate lows down as reactant concentrations decrease, and when ant reactant has a concentration of zero, the reaction stops. What are reaction rate as affected by?
- ATEMPERATURE = more kinetic energy
- BPRESSURE = more molecules in same volume, meaning they are more likely to collide.
- CCONCENTRATION = more molecules in the same volume, and due to them being closer together, they will collide more
- DSURFACE AREA
- EADDING A CATALYST
- FDRAFTS OF AIR
- GIN/COMPLETE COMBUSTION
37The rate of reaction can be calculated by monitoring changes in physical quantities during a reaction:
- Concentration of a reactant or product
- Gas volume of products
- Mass of substances formed or decreasing mass of reactants.
These are plotted against time on a graph, how would you work out the rate?- AGradient.
- BWorkout the distance of the line.
- CYou cannot from a graph, only through calculation.
38The Swedish scientist Jöns Jakob Berzelius was the first person to use the term catalyst while carrying out experiments with [blank_start]hydrogen peroxide[blank_end]. He discovered the addition of certain compounds made the hydrogen peroxide break down [blank_start]faster[blank_end].
Catalysts work by increasing the rate of a chemical reaction without being used up:
- It may react to form an [blank_start]intermediate[blank_end].
- The catalyst is later [blank_start]regenerated[blank_end] so it does not undergo any [blank_start]permanent[blank_end] change.
If a catalyst for a reaction is in the same phase as the reactants, it’s a [blank_start]homogeneous[blank_end] catalyst (e.g. enzymes in body fluids like blood).
If a catalyst is in a different phase, it s a [blank_start]heterogeneous[blank_end] catalyst. If they don’t mix, it can still be heterogeneous if its in a different layer from the reactants. (e.g. catalytic converter in a car is an example. Gases pass over the coasted structure, and are made into less harmful substances).
Catalysts help to [blank_start]lower[blank_end] energy demands, reducing costs and being green. E.g. the Haber process to make ammonia for fertilizer. A lot of energy is needed to break the [blank_start]triple[blank_end] bond in nitrogen, therefore [blank_start]iron[blank_end] catalyses it.- Afaster
- Bhydrogen peroxide
- Cintermediate
- Dregenerated
- Epermanent
- Fhomogeneous
- Gheterogeneous
- Hlower
- Itriple
- Jiron
39For gas or liquid, the molecules move around inside a container, colliding. This is assumed to be elastic and so, when the molecules collide, no energy is lost.
As molecules move they have kinetic energy. In a sample of a gas or liquid, which are correct? (BOLTZMANN DISTRIBUTION)- Athe majority have an average energy.
- Bsome move slow and have low energy.
- Csome molecules move fast and have high energy.
- Dsome molecules have no energy
- Esome molecules have too much energy
40At higher temperatures, the kinetic energy of all the molecules [blank_start]increase[blank_end]. The Boltzmann distribution flattens and shifts to the [blank_start]right[blank_end]. The number doesn't change, so the area remains.
As temperature of reaction increases, the rate of reaction increase as;
- [blank_start]More[blank_end] collisions take place in a certain length of time – the molecules are moving fast and have more [blank_start]energy[blank_end].
- A higher proportion of molecules have an energy that is greater than the [blank_start]activation energy[blank_end] – more collisions will lead to a chemical reaction.
This means that on collision, more [blank_start]molecules[blank_end] in the system will overcome the activation energy of the reaction. There will be more [blank_start]successful[blank_end] collisions in a certain length of time and the rate of reaction
will increase.
Catalysts lower the activation energy of reactions, leading to more molecules being automatically over the activation energy barrier. On collision, more molecules in the system will overcome the new [blank_start]lower[blank_end] activation energy of reaction. There will be more successful collisions= rate of reaction [blank_start]increases[blank_end]- Aincrease
- Bright
- CMore
- Denergy
- Eactivation energy
- Fmolecules
- Gsuccessful
- Hincreases
- Ilower
41Some reactions are reversible, and the sign shows that the reaction is at equilibrium
When a system is in a state of equilibrium, there is no observable change, however, the system is dynamic; it is in constant motion.- AVerdadero
- BFalso
42The extent of a reaction is called the [blank_start]position[blank_end] of equilibrium. Is it not established until the reaction has been occurring for a period of time. It is once the concentrations of reactants/products have become [blank_start]stable[blank_end] and the forward and reverse rates are the same that equilibrium is said to have been established.
The position of equilibrium can be altered by changing the following in the system: [blank_start]concentrations[blank_end], pressure in reactions involving gases and temperatures.
The effect of a change can be predicted using a principle known as le Chateliers principle. This states that when a system in dynamic equilibrium is subject to change, the position of equilibrium will [blank_start]shift[blank_end] to minimize the change.
Changing conditions of the reaction will cause the reaction to adopt the pathway that minimizes the change; this is; carrying out the forward or reverse reaction more, whichever helps [blank_start]minimizes[blank_end] the changes.
For a system at equilibrium, a change in the concentration will result in a shift.
Increasing the conc. of a reactant causes the equilibrium to shift in the direction that decreases this reactants concentration:
- The system opposes the change by decreasing the conc. of reactant by removing it.
- The position moves to the [blank_start]right[blank_end] side, forming for [blank_start]products[blank_end].
Increasing the concentration of a product causes the equilibrium to shift in the direction that decreases this products concentration:
- The system opposes it by decreasing the conc. of the product by removing it.
- The position of equilibrium will move to the [blank_start]left[blank_end] hand side, forming more [blank_start]reactants[blank_end].
Changing the total pressure of a system will only change the position of equilibrium if there are gases present. Increasing total pressure of the system causes the position of equilibrium to move to the side with [blank_start]fewer[blank_end] gas molecules, as this will decrease the pressure.
Decreasing the total pressure of the system causes he position of equilibrium to move to the side with the greater number of gas molecules, as this will [blank_start]increase[blank_end] pressure.
Increasing the pressure of one of the gases in the system is the same as increasing its conc.- Aposition
- Bstable
- Cconcentrations
- Dshift
- Eminimizes
- Fright
- Gproducts
- Hleft
- Ireactants
- Jfewer
- Kincrease
43The effect of changing temperature on the position of the equilibrium depends on the enthalpy sign. In figure 1, the forward reaction is exothermic, and the reverse reaction is endothermic (+92kJmol-1).
Increasing temperature causing the equilibrium to move in the direction that [blank_start]decreases[blank_end] the temperature. The system opposes the change by taking in heat and it moves to the [blank_start]left[blank_end] (moves in the endothermic direction).
[blank_start]Decreasing[blank_end] the temperature of the system causes the position of equilibrium to move in in such a way as to increase the temperature. The system opposes the change by releasing [blank_start]heat[blank_end] and the position of equilibrium moves to the right. The position of equilibrium moves in the [blank_start]exothermic[blank_end] direction.
A catalyst doesn’t alter the [blank_start]position[blank_end] of equilibrium or the composition of an equilibrium system. A catalyst speeds up to react of both reactions equally. A catalysts increases the rate the equilibrium is established.- Adecreases
- Bleft
- CDecreasing
- Dheat
- Eexothermic
- Fposition
44Many important chemical processes exist as equilibrium systems. Which of these are they?
- AThe preparation of ammonia from nitrogen and hydrogen in the Haber process.
- BThe conversion of sulfur dioxide into sulfur trioxide in the contact process.
- CThe production of Hydrochloric Acid.
- DOxidisation of secondary alcohols into Ketones.
45Chemists strive to achieve the highest possible yield of a desired product. However, this has to be balanced against the optimum position of equilibrium, which allows industrial processes to be as cheap and energy efficient as possible. Raw materials must be readily available, but what is also needed for ammonia production?
- AHigh Pressure, Low Temp
- BHigh Pressure, High Temp
- CLow Pressure, Low Temp
- DLow Pressure, High Temp
46What are the drawbacks of the required ammonia environment?
- AAlthough the temperature should produce a high yield,
the reaction would take place a very low rate. (not enough
energy to overcome the required activation energy). - BThe pressure increases the concentration of the gases,
increasing reaction rate. However, large quantities of energy are required to compress gases, adding runny costs. Also any failure in the systems could allow chemicals o leak into the environment. - CBoth conditions require too much money to keep at, therefore most companies lose money instead of making profits.
- AAlthough the temperature should produce a high yield,
47When a reaction has reached equilibrium, the concentrations of each species involved remain [blank_start]constant[blank_end]. In a concentration of the products is higher than that of the reactants it moves to the [blank_start]right[blank_end]. If the reactants concentration is higher, it lies to the [blank_start]left[blank_end] and favors them.
Chemists consider the position of an equilibrium using the constant Kc. It gives a measure of where it lies by giving the [blank_start]ratio[blank_end] between products and reactants.
The size of Kc will give an indication of the position of equilibrium. Once an expression has been determined, concentrations of each species must be established, which is done [blank_start]experimentally[blank_end].
A Kc value of 1 indicates its halfway between reactants and products, ratio = 1:1
When Kc is greater than one, the reaction favors the [blank_start]products[blank_end] (right), the products on the right hand side predominate at equilibrium.
When Kc is smaller than one, the reactant favors the reactants ([blank_start]left[blank_end]), the reactants of the left hand side predominate at [blank_start]equilibrium[blank_end].- Aconstant
- Bright
- Cleft
- Dratio
- Eexperimentally
- Fproducts
- Gleft
- Hequilibrium
Información
- Descripción
- A level Chemistry Test sobre MODULE 3, creado por Molly Butcher el 11/04/2017.
- Autor
- Molly Butcher
- Idioma
- English
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