Equilibria and Kc

Question 1

Effect of a catalyst on the position of equilibrium

Answer 1

Speeds up forwards reaction and backwards reaction equally

no affect on yield

Question 2

Features of a dynamic equilibrium

Answer 2

forwards rate= backwards rate

concentrations remain constant

Question 3

Le chateliers principle

Answer 3

Equilibrium will shift to oppose change

Question 4

Finding Kc using practical methods

Answer 4

CH3COOH+CH3CH2CH2OH-CH3COOCH2CH2CH3+H2O
Slow reaction even with H2SO4 catalyst and will have to leave mixture for a week to reach equilibrium
Add water to create a volumetric solution to then titrate without change in equilibrium, this measures the H+ concentration which is a combination of the left over ethanoic acid and acid catalyst (known concentration)
can calculate moles of equilibrium of ethanoic acid.

Question 5

effect of Concentration on equilibrium reactions

Answer 5

A+B<->C+D

Increase in A, system shifts to oppose change, so equilibrium shits right to react A and lower its concentration

Question 6

effect of Pressure on equilibria reactions

Answer 6

only affects reactions involving gasses
increase in pressure the equilibrium shifts to oppose the increase.
Shifts to the side with the lease moles of gas

Question 7

effect of temperature on equilibria reactions

Answer 7

increase in temperature causes the equilibrium to shift to oppose the increase.
Shifts in the endothermic direction to reduce the temperature

Question 8

Haber process

Answer 8

N2+3H2<->2NH3
temperature- exothermic so highest yield at lower temperatures however the reaction is slow so a compromise temperature is needed

pressure- favoured at high pressure as there are fewer gas moles but it is expensive to produce high pressures and complex equipment is needed.

Question 9

Production of ethanol

Answer 9

H2C=CH2+H2O<->CH3CH2OH
uses- cosmetics, drugs, detergents
concentrated phosphoric acid catalyst

temp- moderate to favour forwards reaction but not too slow as to reduce rate too much

pressure- moderate as pressure favours forward reaction but is expensive

Question 10

conditions for equilibrium

Answer 10

-only reached in a closed system, the reactants/products cant escape
-no reactants or products added or removed
equilibrium reached when properties dont change with time

Question 11

effect of change in reaction conditions of Kc

Answer 11

only effected by temperature
this causes concentrations to change which affects Kc