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Equilibrium
Fichas del conjunto (26)
- 1How is an equilibrium reaction portrayed?Reversible reactions are shown with arrows going both ways
At equilibrium, there are no observable changes, however, the forward and reverse reactions are still happening (the reaction is dynamic)
A + B ---> <--- C + D - 2What is meant by dynamic equilibrium?Most reactions don't go to completion. Once some products are formed, the reverse reaction can take place and reform the reactants
In a closed system, concentrations of all reactants and products will eventually become constant - such a system is said to be in dynamic equilibrium - 3What happens in dynamic equilibrium?The forward and revers reactions occur at the same rate at equilibrium
There is no change in concentration of reactants or products
The system must be closed - no changes in external conditions - 4What is meant by a closed system?Neither matter nor energy can be lost or gained from the system - macroscopic properties remain constant
(If the system was open, some of the products from the reaction could escape and equilibrium would never be reached) - 5What is Kc?Kc (the equilibrium constant) gives a measure of the ratio of equilibrium concentrations and indicates to whether equilibrium lies to the left or right hand side
Kc only changes if the temperature does
aA + bB --><-- cC + dD
Kc = ([C]c eqm x [D]d eqm)/ ([A]a eqm x [B]b eqm)
The units of Kc change for each reaction - 6What is and what changes the magnitude of Kc?Since the equilibrium expression has the concentrations of products on top and concentrations of reactants on the bottom, it follows that the magnitude of the equilibrium constant is related to the position of equilibrium
*When the reaction is near completion: Kc > 1 and eqm lies to RHS (products)
*When the reaction hardly proceeds
Kc < 1 and eqm lies to LHS (reactants) - 7What does an increase in temperature do to Kc?Kc is smaller and equilibrium shifts to the left hand side
Increase in temperature will always shift equilibrium to the endothermic side - 8What is the reverse reaction when using Kc?The reverse reaction is the reciprocal of Kc
(reverse reaction) = 1/Kc - 9What does Le Chatelier's principle state and what factors affect it?When a change is made to a system in a dynamic equilibrium, the position of equilibrium shifts (to LHS or RHS) to minimise the change
Changes this applies to are
~ Temperature
~ Pressure
~ Concentration
~ Catalysts (which actually have no effect as speed up forward and reverse reaction equally) - 10What happens to the position of equilibrium due to temperature increase or decrease according to Le Chataleirs principle?INCREASE
Shifts to the left (endothermic) to decrease temperature
DECREASE
Shifts to right (exothermic) to increase the temperature (also will increase pressure) - 11What happens to the position of equilibrium due to pressure increase or decrease according to Le Chataleirs principle?INCREASE
Shifts to side with less gas particles
DECREASE
Shifts to side with more moles of gas - 12What happens to the position of equilibrium due to concentration increase according to Le Chataleirs principle?(of reactants) or decrease in products (taken away) will shift equilibrium to the right (towards the products)
- 13What is meant by the position of equilibrium?Shows the extent of the reaction (can lie towards the products (RHS) or the reactants (LHS)
- 14What factors affect position of equilibrium?1. Change in concentration
2. Change in pressure
3. Change in temperature
4. Adding a catalyst - 15How is equilibrium used in industry?Chemists adjust the condition of reactions to try and increase the yield of products. They need to consider equilibrium and Le Chateleir's principle when altering the conditions
- 16How is equilibrium principles used in the Haber Process?Ammonia is used in fertilisers and is manufactured in the production of nitric acid
N2+ (g) + 3H2 (g) --><-- 2NH3 (g)
The hydrogen obtained from natural gas. The nitrogen from the fractional distillation of liquid air
Based on the conditions, to increase the yield of NH3, you could
1. Increase the pressure (less moles of gas on RHS) this will increase the number of particles per unit volume, therefore increasing rate at which equilibrium is reached
2. Lower the temperature (eqm shifts to RHS)
3. Increase concentration of N2 or H2 Or decrease of NH3
4. Add a catalyst - 17What are the problems with the potential conditions for the Haber process and what conditions are actually used?PROBLEMS
High pressures are expensive and dangerous
Low temperatures decrease the rate of reaction
ACTUAL CONDITIONS
450oC
250 ATM pressure
Powdered iron catalyst
NH3 removed as product
(Even with all of these, yield of ammonia
is only 15%) - 18How are equilibrium principles used in the Contact Process?Sulphuric acid is manufactured in the contact process. It is the most industrially produced chemical, over 150 million tonnes produced per year. Used in fertilisers, paints, detergents and feedstock for other chemicals
2SO2 (g) + O2 (g) --><-- 2SO3 (g)
the sulphur dioxide is obtained from burning sulphur or sulphur ores. Oxygen from the fractional distillation of air
BASED ON CONDITIONS DO;
1. 3 volumes are converted to two volumes, so high pressures, as there are less moles of gas on the RHS
2. The reaction is exothermic, so lower temps - 19What are the actual conditions used for the contact process?V2O5 (Vandium Oxide) catalyst
400oC
2 ATM pressure (very low)
This gives a 99% yield, so is uneconomical to make higher - 20How would you calculate Kc when equilibrium concentration are not initially known?To calculate Kc, we must have the equilibrium concentrations for all reactants and products
If one concentration is known, use the balanced equation and the ICE method
SEE BOOK FOR METHOD - 21Define the enthalpy of vapourisationthe energy required to convert one mole of liquid to a vapour under standard condition (298K, 1 ATM)
H2O (l) --> H2O (g) - 22When does dynamic equilibrium occur between and liquid and its vapour?When the rate of vaporisation is equal to the rate of condensation
The vapour pressure of a liquid is the pressure exerted by the particles in the vapour phase - 23What factors affect the vapour pressure?the vapour pressure of any liquid depends on both the strength of the molecular forces holding the liquid together and on the temperature
deltaHvap depends on the intermolecular forces present. The stronger the IM forces, the high deltaHvap
Vapour pressure is the pressure exerted by the vapour in equilibrium with the liquid. As we increase the temperature, the vapour pressure increases exponentially. At 1 ATM pressure, the boiling point of water is 100oC
VAPOURISATION IS ENDOTHERMIC - 24What is the enthalpy of vaporisation independent of?the surface area of the liquid or the size of the container, although in a bigger container, it may take longer for the equilibrium to become established
- 25What is the relationship on bubble formation in water and vapour pressure?Bubbles are water vapour
When boiling, the bubbles of water cannot form until the vapour pressure = the external force - 26What is the relationship between I.M forces, deltaHvap, boiling points and lower vapour pressure?Stronger the IM forces, the higher the deltaHvap, the higher the boiling point and the lower the vapour pressure
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- IB Chemistry Fichas sobre Equilibrium, creado por P H el 02/03/2015.
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- P H
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