Le Chatelier's Principle - Equilibria Pt A - (4.1)

Question 1

What is a reversible reaction?

Answer 1

• A system in which the reactants react to make products, but the products in turn can react to make reactants again
• Eventually an equilibrium is reached

Question 2

Explain what is meant when the reaction is at equilibrium

Answer 2

1. Both the forward & backward reactions take place continuously
2. The rate of the forward reaction equals the rate of the reverse reaction
3. The concentration of the reactants are constant & the concentration of the products are constant (but are not the same)
4. It requires a closed system (one from which no substances can escape)

Question 3

On a graph of reactants (or products) concentration against time, what happens to the curve that suggests an equilibrium has been reached?

Answer 3

• It starts to form a plateau
• suggesting that the reactant/product concentration is remaining constant
• (the rate at which it is produced - this plateau aligns with the graphs for both reactants & products suggesting the rate of forward & backward reaction are equal further justifying that it is at equilibrium)

Question 4

What does the position of the equilibrium show?

Answer 4

It is a measure of the percentage of the reactants that are converted to products

Question 5

What does it suggest about the reaction if the equilibrium lies on the left?

Answer 5

• Less than half the reactants are converted to products

- Low yield of product

Question 6

What does it suggest about the reaction if the equilibrium lies on the right?

Answer 6

• More than half the reactants are converted to products

- High yield of product

Question 7

What does Le Chatelier’s Principle state?

Answer 7

A system at equilibrium will do everything it can to resist any change

Question 8

Using Le Chatelier’s Principle, what will happen if you raise the temperature?

Answer 8

The system will try to cool it down

Question 9

Using Le Chatelier’s Principle, what will happen if you raise the pressure?

Answer 9

The system will try to reduce the pressure

Question 10

Using Le Chatelier’s Principle, what will happen if you increase the amount of the substance (concentration)?

Answer 10

The system will try to remove it

Question 11

Explain what will happen if you increase the concentration of reactants (use Le Chatelier’s Principle)

Answer 11

• The system is no longer at equilibrium so it will resist the change
• It will remove extra reactants by promoting the forwards reaction
• The position of the equilibrium will shift to the right

Question 12

Explain what will happen if you increase the pressure (use Le Chatelier’s Principle)

Answer 12

• If there are a different no. of moles on reactant & product side this would cause the system to reduce pressure
• done by reducing the no. of moles of the side with more moles, shifting the equilibrium from the side with more moles to the side with less

Question 13

Explain what will happen if you decrease the temperature of an endothermic reaction (use Le Chatelier’s Principle)

Answer 13

• Decreasing temp. will cause system to resist this change by increasing temp.
• The reaction is endothermic which means it decreases temp. so the equilibrium will shift to the left (to increase temp.)

Question 14

How do catalysts affect equilibrium?

Answer 14

• They have NO effect on the position of an equilibrium
• They accelerate both the forward & reverse reactions equally
• Ensure equilibrium condition is reached more quickly (which is very important in industrial reactions)