Equilibria

Question 1

What is Le Chatelier’s principle?

Answer 1

If a system is disturbed it reacts to counteract the change.

Question 2

State the relationship between delta S total and the equilibrium constant.

Answer 2

Delta S total = RlnK

Question 3

Define partial pressure.

Answer 3

The pressure a gas would exert if it occupied a single volume alone.

Question 4

How do you calculate partial pressure?

Answer 4

PP = total pressure * mole fraction

Question 5

Define:

a) Temperature

b) Pressure

Answer 5

a) Temperature: the average kinetic energy of particles in a system.
b) Pressure: the amount and strength of collisions of particles against a vessel (depends on frequency, strength and speed (kinetic energy)

Question 6

State the effect on the position of equilibrium of an increase in:

a) temperature
b) pressure

Answer 6

a) for an exothermic reaction: eqm shifts to the left (the endothermic side)
for an exothermic reaction: eqm shifts to right (the endothermic side)
b) pressure: shifts to the side with the fewer number of gaseous molecules

Question 7

In reality, industrial processes cannot be in equilibrium because the products are removed. Give a few aims of industrial processes.

Answer 7

1. To increase the rate of reaction
2. To maximise the yield and atom economy (minimise waste)
3. To keep costs low
4. To use safe, economically viable conditions

Question 8

How can you maximise the yield of product?

Answer 8

Collect the product as it forms.

Recycle any unreacted reactants.

Question 9

Define dynamic equilibrium and state two conditions.

Answer 9

The rates of the forwards and reverse reactions are equal.
There is no further change to the concentrations of the reactants and products (they are constant) and it happens in a closed system.

Question 10

Why is the number of moles of water present at equilibrium greater than the number of moles of ester in a reaction between alcohol and carboxylic acid?

Answer 10

Hydrochloric acid contains some water (despite HCl being a gas).

Question 11

Explain the effect of increasing the temperature on the equilibrium constant.

Answer 11

Endothermic reaction: Increases K, (becomes larger than the quotient). Equilibrium shifts to the right to increase Q (numerator increases and the denominator decreases).
Exothermic reaction: Decreases K so K is smaller than Q. Equilibrium shifts to the left to decrease the numerator and increase the denominator so Q becomes equal to K.