1.6 Equilibria

Question 1

How do you establish equilibrium?

Answer 1

There are only reactants when the reaction starts as no products have been formed
The rate of forward reaction decreases as reactants used up
The rate of backwards reaction speeds up as there is an increase in the amount of products
The rate of forward reaction will then equal the backwards reaction

Question 2

Dynamic definition

Answer 2

The forward and backward reaction proceed at equal rates

Question 3

Equilibrium definition

Answer 3

The concentration of the reactants and products are constant

Question 4

When is the only time dynamic equilibrium can be reached

Answer 4

In a closed system

Question 5

State Le Chateliers Principle

Answer 5

The position of the equilibrium will shift to oppose the change made to it

Question 6

CO + H2O = CO2 + H2
Concentration of CO increased

Answer 6

The equilibrium will shift to the right to oppose the addition of CO
SO the yield of CO2 and H2 will increase

Question 7

2NO2 = N2O4
pressure increased

Answer 7

There are fewer moles on the right
The equilibrium will shift to the right to oppose the increase in pressure
The yield of N2O4 increases

Question 8

When would changing the pressure not affect the equilibrium

Answer 8

when there is an equal number of moles of product and reactant

Question 9

What happens to the pressure when the volume decreases?

Answer 9

Pressure increases

Question 10

What happens to the volume when the pressure decreases?

Answer 10

Volume increases

Question 11

CH4 + H2O = CO + 3H2
Explain why increasing the volume of the reaction container increases the equilibrium yield of hydrogen

Answer 11

Increasing the volume decreases the pressure
There are more moles on the right
The equilibrium shifts to the right tom oppose the decrease in pressure so the yield of hydrogen increases

Question 12

What happens in exothermic reactions?

Answer 12

• Releases heat energy
• Temperature of the surroundings increases
• Enthalpy change is negative

Question 13

What happens in endothermic reactions?

Answer 13

• Absorbs heat energy
• Temperature of surroundings decreases
• Enthalpy change is positive

Question 14

CH4 + H2O = CO + 3H2
Enthalpy change = -206
Temperature of reaction decreased

Answer 14

• Forward reaction is exothermic
• The equilibrium shifts to the right to oppose the decrease in temperature
• Yield of CO2 and H2 increases

Question 15

What is a catalyst?

Answer 15

A substance that speeds up the rate of reaction by providing an alternative reaction pathway with a lower activation energy

Question 16

What happens when a catalyst is added to the reaction?

Answer 16

• The rate of both the forward and reverse reactions increase equally
• There is no change to the position of the equilibrium
• The dynamic equilibrium is reached faster

Question 17

Why are catalysts added to the haber process?

Answer 17

To reduce the time taken to reach the dynamic equilibrium

Question 18

What are compromise conditions used for?

Answer 18

To produce the maximum yield in the shortest amount of time for the least cost

Question 19

What is the equation for Kc?

Answer 19

Kc = [products] / [reactants]
The square brackets mean concentration

Question 20

Which way does the equilibrium shift if Kc is above 1?

Answer 20

There are more products than reactants so the equilibrium shifts to the right

Question 21

Which way does the equilibrium shift if Kc is less than 1?

Answer 21

There are more reactants than products so the equilibrium shifts to the left

Question 22

What happens if the Kc is equal to 1?

Answer 22

The concentration of products are equal to the concentration of reactants

Question 23

When is the value of Kc not changed?

Answer 23

When there is changes in concentration, pressure and use of a catalyst

Question 24

What is the only thing that changes the value of Kc?

Answer 24

Temperature

Question 25

What is the process to find Kc from the concentrations of reactants and products at equilibrium?

Answer 25

• Initial amount of each product and reactant
• Change in each reactant
• Equilibrium number of moles for each product and reactant
• Equilibrium concentration of each reactant
• Kc expression and calculation
• Units