6.1 The idea of equilibrium

Question 1

What is an equilibrium mixture

Answer 1

The mixture of reactants and products formed when a reversible reaction is allowed to proceed in a closed container until no further reaction change occurs.
The forward and backward reactions are still proceeding but at the same rate

Question 2

What are the conditions for equilibrium

Answer 2

. Closed system (one where the reactants and products can’t escape)
Eg a beaker, but a lid isn’t necessary as long as the reactants aren’t evaporating

. Equilibrium can be approached from either direction eg from liquid to vapour or from vapour to liquid (as long as temp and pressure stay the same)

. Equilibrium is dynamic, so when the rates of the two opposing processes are the same

Question 3

How do you know when equilibrium has ben reached

Answer 3

. The macroscopic properties of the system do not change with time.
Eg density, concentration, colour and pressure.

Question 4

What is dynamic equilibrium

Answer 4

Situation where the composition of a constant composition reaction mixture does not change because the forward and backward reactions are proceeding at the same rate

Question 5

Describe the process of a reaction reaching equilibrium

Answer 5

At the start of a reaction, the rate of forward reaction is fast because the reactants are plentiful, and there is no reverse reaction because there are no products yet

As the concentrations of the products start to increase, the reverse reaction speeds up, and the reaction of reactants slows down as concentration of reactants decreases

A point is reached where there are the same number of particles changing from products to reactants as there are particles changing from reactants to products

Question 6

Is the equilibrium mixture always half reactants half products

Answer 6

No, there can be any proportions of reactants and products
The proportions change depending on conditions of reaction eg temp, pressure and concentration

But at constant conditions, the proportions will not change

Question 7

Two features of dynamic equilibrium

Answer 7

. The concentration of products and reactants are not changing

. The rate of reaction for forward and backward reactions are equal