Reversible Reactions and Equilibria (1)

Question 1

Define

reversible reaction.

Answer 1

a reaction where the products of the reaction can themselves react to produce the original reactants

Question 2

Define

dynamic equilibrium.

Answer 2

a state in which the amounts of reactants and products reach a balance

(their concentrations stop changing)

Question 3

What three things that

change the position of equilibrium of a reaction?

Answer 3

• temperature
• pressure (when some or all of the products or reactants are gases)
• the concentrations of reactants or products

Question 4

What is

Le Chatelier’s principle?

Answer 4

the idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change

so, by altering the temperature, pressure or concentration of the reactants, you can alter the yield of the reaction - making sure that you end up with more of the product you want

Question 5

How can altering the

temperature of a reversible reaction move the equilibrium?

and why?

Answer 5

If the temperature is risen, the equilibrium will move in the endothermic direction. (So the yield of the endothermic reaction will increase and vice versa.)

The opposite is true if you lower the temperature.

This is because all reversible reactions are exothermic in one direction and endothermic in the other.

Question 6

How can altering the

pressure of a reversible reaction move the equilibrium?

and why?

Answer 6

If the pressure is risen, the reaction which produces less volume will be favoured (and the equilibrium will move more to that side).

The opposite is true if you lower the pressure.

This is because many reactions have a greater volume on one side.
Greater volume means that there are more gas molecules on that side of the equation.

Question 7

How can altering the

concentration of reactants (or products) of a reversible reaction move the equilibrium?

and why?

Answer 7

If the concentration of reactant is increased, the system tried to decrease it by making more products.

The opposite is true if you increase the concentration of products.

This is because the system will no longer be at equilibrium, so the system will respond to bring itself back to equilibrium again.