ES7: Le Chatelier

Question 1

What is “Le Chatelier’s Principle”?

Answer 1

When a change is applied to a system in dynamic equilibrium, the system reacts in such a way to oppose the effect of the change

Question 2

What happens when the concentration of a reactant is increased?

Answer 2

• The position of equilibrium moves to the right
• So the forward reaction occurs increasingly
• More reactants are turned into products

Question 3

What happens when the concentration of a product is increased in a dynamic equilibrium?

Answer 3

• The position of equilibrium moves to the left
• So the reverse reaction occurs increasingly
• More products are turned back into reactants

Question 4

Does Kc change when the concentration of either a product/reactant is increased?

Answer 4

No, it is constant

Question 5

Why doesn’t Kc change when the concentration of either a product/reactant is increased?

Answer 5

Because concentrations of other reagents change to keep Kc constant

Question 6

What happens when the pressure is increased in a dynamic equilibrium?

Answer 6

• Shifts equilibrium to the side with fewer gas molecules

- Less particles in a given volume are produced, which decreases the pressure

Question 7

What happens when the pressure is decreased in a dynamic equilibrium?

Answer 7

• Shifts equilibrium to the side with more gas molecules

- More particles in a given volume are produced, which increases the pressure

Question 8

What happens when the pressure is increased/decreased in a dynamic equilibrium with the same number of gaseous molecules on both sides of the reaction?

Answer 8

The position of equilibrium does not change

Question 9

What happens when the temperature is increased in a dynamic equilibrium?

Answer 9

• Increased temperature means added heat

- Position of equilibrium will shift in the endothermic reaction direction to absorb heat

Question 10

What happens when the temperature is increased in a dynamic equilibrium?

Answer 10

• Decreased temperature means removing heat

- Position of equilibrium will shift in the exothermic reaction direction to increase heat

Question 11

Is an exothermic enthalpy value negative or positive?

Answer 11

Negative

Question 12

Is an endothermic enthalpy value negative or positive?

Answer 12

Positive

Question 13

Does Kc change when changing pressure?

Answer 13

No

Question 14

Does Kc change when changing temperature?

Answer 14

Yes

Question 15

Do catalysts change Kc or the position of equilibrium?

Answer 15

No

Question 16

Why don’t catalysts change Kc or the position of equilibrium?

Answer 16

They speed up the forwards and backwards reaction to the same extent

Question 17

What to catalysts change about a reversible reaction?

Answer 17

They speed up the time it takes to get to dynamic equilibrium