3.8 Le Chateliers principle

Question 1

Reversible reaction definition

Answer 1

A reaction where the reactants can turn into products and the products can turn into reactants

Question 2

How is dynamic equilibrium is reached

Answer 2

The forward rate of reaction is fast, the backwards rate of reaction is slow
The backwards rate of reaction increases as the forward rate of reaction slows down
The forward and backwards rate of reaction is slow

Question 3

Explain how a dynamic equilibrium is reached

Answer 3

The forwards rate of reaction is fast as it is only reactants, they are being made into products. this slows down as the reactants are used up.
The backwards rate of reaction is slow as there are no products yet to be made into reactants. This increases as the reactants are turned into products, there are more products available. The forwards and backwards rate of reaction equals as the products and reactants are formed at the same rate

Question 4

Dynamic equilibrium definition

Answer 4

Dynamic - forward and backward reaction proceed at equal rate
Equilibrium - Concentration of reactants and products are constant

Question 5

When is the only time dynamic equilibrium be reached?

Answer 5

In a closed system

Question 6

Which side is the equilibrium on if there are more products than reactants?

Answer 6

Right

Question 7

Which side is the equilibrium on if there are more reactants than products?

Answer 7

Left

Question 8

Le Chateliers principle definition

Answer 8

The position of the equilibrium shifts to oppose the change

Question 9

CO + H2O –> CO2 + H2
CO increased

Answer 9

Equilibrium shifts to the right to oppose the increase in CO
The yield of CO2 and H2 increases

Question 10

2NO2 –> N2O4
Pressure increased

Answer 10

The left side has more moles so has a higher pressure
The equilibrium shifts to the right to oppose the increase in pressure
The yield of N2O4 increases

Question 11

What happens to the position of the equilibrium if there is an equal number of moles on each side?

Answer 11

The position of the equilibrium is not affected

Question 12

What happens to the pressure if there is a decrease in volume?

Answer 12

There is an increase in pressure

Question 13

What happens to the pressure if there is an increase in volume?

Answer 13

There is a decrease in pressure

Question 14

CH4 + H2O –> CO + 3H2
Increase in volume

Answer 14

Increasing the volume decreases the pressure
The right side has more moles so has a higher pressure
the equilibrium shifts to the right to oppose the increase in volume
The yield of CO and H2 increases

Question 15

What happens in exothermic reactions?

Answer 15

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

Question 16

What happens in endothermic reactions?

Answer 16

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

Question 17

If the forward reaction is exothermic, what is the backwards reaction?

Answer 17

Endothermic
They are opposite

Question 18

CH4 + H2O –> CO + 3H2
Enthalpy = -206 kj mol-1
Temperature decreased

Answer 18

COLD –> HOT
The forward reaction is exothermic
The equilibrium shifts to right side to oppose the change in temperature
The yield of CO and H2 increases

Question 19

What is a catalyst?

Answer 19

A substance that speeds up the rate of reaction by lowering the activation energy by providing an alternate reaction pathway

Question 20

What happens when a catalyst is added to a reversible reaction?

Answer 20

The rate of the forwards and backwards reaction increases equally
There is no change in the position of the equilibrium
A dynamic equilibrium is reached faster

Question 21

Why are compromise conditions used?

Answer 21

To increase the amount of yield produces in the least time and money

Question 22

What is Kc?

Answer 22

conc of products/ conc of reactants

Question 23

What happens when Kc > 1?

Answer 23

The equilibrium shifts to the right and more product is formed

Question 24

What happens when Kc < 1?

Answer 24

Equilibrium shifts to the left, more reactants is formed

Question 25

What happens when Kc = 1?

Answer 25

No effect on equilibrium, equal amounts of products and reactants formed

Question 26

How does an increase in pressure alter Kc?

Answer 26

Pressure doesn’t affect Kc, only temperature