Reversible Reactions

Question 1

Explain dynamic equilibrium

Answer 1

As the reactants get used up, the forward reaction slows down - and as more product is formed, the reverse reaction speeds up. After a while, the forward reaction will be going at exactly the same rate as the backwards reaction so the amounts of reactants and products won’t be changing anymore. This is dynamic equilibrium

Question 2

Dynamic equilibrium can only happen in what?

Answer 2

A closed system - this means nothing can get in or out

Question 3

How do you alter the position of quilibrium?

Answer 3

If you change the concentration, pressure or temperature of a reversible reaction, you alter the position of equilibrium

Question 4

Define Le Chatelier’s principle

Answer 4

If a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change

Question 5

Le Chatelier’s principle only applies to what type of equilibria?

Answer 5

Homogeneous equilibria - this is where every species is in the same physical state

Question 6

How does changing the concentration affect equilibria?

Answer 6

If you increase the concentration of a reactant, the equilibrium tries to get rid of the extra reactant. This makes the forward reaction go faster, so equilibrium shifts to the right.

If you increase the concentration of a product, the equilibrium tried to remove the extra product. This makes the reverse reaction go faster, so equilibrium shifts to the left

Question 7

How does changing the pressure affect equilibria?

Answer 7

Increasing the pressure shifts equilibrium to the side with fewer gas molecules. This reduces the pressure

Decreasing the pressure shifts equilibrium to the side with more gas molecules. This increases the pressure

Question 8

How does changing the temperature affect equilibria?

Answer 8

Increasing the temperature means adding heat. The equilibrium shifts in the endothermic direction to absorb this heat

Decreasing the temperature means removing heat. The equilibrium shifts in the exothermic direction to produce more heat

Question 9

Do catalysts affect the position of equilibrium?

Answer 9

Catalysts have no effect on the position of equilibrium. They can’t increase yield but they do mean equilibrium is reached faster

Question 10

In industry, how are reaction rates chosen?

Answer 10

Companies have to think about how much it costs to run a reaction and how much money they can make from it. This means that reaction conditions chosen are a compromise