Karteikarten
A2 OCR Chemistry; Energy
Karten in diesem Stapel (18)
- 1What is the definition for Lattice Enthalpy, (∆leH°)?is the enthalpy change that accompanies the formation of one mole of an ionic lattice from its gaseous ions under standard conditions
- 2What is the definition of Standard Enthalpy of Formation, (∆fH°)?is the enthalpy change that accompanies the formation of 1 mole of a compound from its constituent elements in their standard states
-usually exothermic for an ionic compound because bonds are formed - 3What is the definition for First Ionisation Energy, (∆I1H°)?is the energy change that accompanies the removal of one mole of electrons from one mole of gaseous atoms
-endothermic process because the e- being lost has to overcome the attraction from the nucleus in order to leave the atom - 4What is the definition for the first electron affinity, (∆EA1H°)?is the opposite of ionisation energy, the addition of e- rather than the removal of e-
is the energy change associated with the addition of one more of electrons, to form one mole of gasepus atoms from one mole pf gaseous 1- ions - 5What is the definition for the Standard Enthalpy Change of Solution, (∆solH°)?is the enthalpy chamge that takes place when one mole of a solute is completrly dissolved in water under standard conditions
two processess take place when a solid dissolves:
1. Ionic lattice breaks down
2. Free ions become part of solution (hydration)
-lattice enthalpy has a negative sign and is exothermic - 6What is the definition for the Standard Enthalpy Change of Hydration, (∆hydH°)?is the enthalpy change that takes place when dissolving one mole of gaseous ions in water
break down of the ionoc lattice has a positive sign and is endothermic
Ionic lattices dissolve in polar solvents such as, water
Energy is released when new bonds form between water and the ions - 7What dictates the size of the lattice enthalpy?magnitude of lattice enthalpy depends on:
1. Size of ions involved
2. Charges on the ions
3. Ionic bond strength
(dependent of ionic size and charge)
-Smaller ions (can get closer together, have smaller ionic radius) attracts one another more strongly, gives rise to more exothermic lattice enthalpy values
-Ions with higer charges have stronger electrostatic attractions and so more exothermic lattice enthalpy values
most exothermic values are from, small ions with a high charge
applies to enthalpy of hydration (so ions with water molecules) - 8What is the definition of entropy, S?is the quantitive measure of the degree of disorder in a system
the more disorded the particles are in a system, the higher the entropy of the system
solid has a low disorder compared to gas - 9What is the definition of Standard Entropy, S°?of a substance is the entropy content of one mole of the substance under standard conditions
have the units, J K-1 mol-1
all substances above 0K possess a certain degree of disorder because they are in constant motion, so:
1. entropy, S, is always a positive number
2. at 0K, entropy is 0 for perfect crystals
more probable a more disorded system will be found instead of a more ordered system
more spreading out of energy= higher entropy
more random arrangements of particles= higher entropy - 10What is the Standard Entropy Change of Reaction, ∆S°?is the entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states
entropy can change during the course of a chemical reaction, noted as a change in entropy
although there is a tendency towards higher entropy, it is possible for entropy to decrease, for ∆S to be negative.
E.g: Water to Ice, disordered liquid becomes a more ordered solid, has lower levels of energy dispersal
∆S = sum of S°products- sum of ∆S reactants
change makes a system more random = ∆S is +
change makes a system more ordered = ∆S is - - 11How is entropy affected by temperature?Entropy of pure substances increase with increasing temperature
values are given per K-1 (because entropy values are dependent on temp)
-arrangement of particles at higher temp becomes more random
-Entropy of solids < liquids < gases - 12How do the number of gaseous molecules affect the entropy?numbrr of gaseous molecules changes during a reaction then entropy increases
increase in gaseoua molecules= increase in entropy
decrease in gaseous molecules= decrease in entropy - 13What is free energy change, ∆G?is the balance between, enthalpy, entropy and temperature for a process:
∆G = ∆H - T∆S
a process can take place spontaneously when ∆G < ∆
for a process to occur spontaneously entropy must increase, however there are many reactions that happen spontaneously that would seem to lower energy - 14What is the total change in entropy?∆S°total= ∆S°system -∆S°surroundings
reactions that have a decrease in entropy can happen spontaneously if the change in entropy of the surroundings is positive enough the make the total change is entropy positive - 15How is the Gibb's equation and Free Energy Change associated?energy that becomes 'free' during a reaction is known as Gibbs' free energy after theoretical physicist and mathematician, John Willard Gibbs
dependent on total entropy, enthalpy changes that occur and temperature
for reactions to occure spontaneously, ∆G must be negative
∆G = ∆H - T∆S
∆S°total= ∆S - (∆H÷T)
rearranged to: -T∆Stotal = ∆H - T∆S
converted to Gibbs equation: ∆G = -T∆S - 16How can you use Gibbs equation to predict feasibility of reactions?-Large increases in entropy will cause decreases in ∆G, because the term -T∆S will become larger
-Large negative values for ∆H(highly exothermic reactions), will result in more negative values for ∆G
If a highly exothermic reaction causes a large decrease in entropy, ∆G, may be positive, in which case the change would not be spontaneous - 17in summary of last flashcard:-exothermic reactions are generally spontaneous-negative values of ∆H is still able to make ∆G negative, even if the entropy change is positive
-endothermic changes are only positive if the entropy changes are positive and the temperature is high enough to make T∆S large and positive, i.e greater than ∆H - 18What are the limitations of using ∆G to predict feasibility of reactions?-calculating values ale of ∆G gives a theoretical value for whether a reaction will occur spontaneously
-If a reaction is found to have a negative value of ∆G, it does not mean it will go on to react
-whether or not a reaction process also depends on kinetic factors:
1. Reaction may have a high Ea
2. Rate of reaction may be very slow
Read cross that have a positive value of ∆G are considered not feasible, but can be made to take place by changing the temperaturtemperaturen of the reaction
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- Short quiz to test your energy knowledge
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- Kellie Mayes-Barwick
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