Equilibria

Question 1

What happens when a reversible reaction reaches equilibrium?

Answer 1

The rate of forward and reverse reactions are equal

Question 2

Write an expression for Kc for the following reaction:
2A + B –> C + 3D

Answer 2

[C] x [D]^3 / [A]^2 x [B]

Question 3

Define the term dynamic equilibrium

Answer 3

When a reversible reaction is in a closed system, the rate of the forward and reverse reactions are the same, and remain at a constant rate

Question 4

What factor affects the value of Kc ?

Answer 4

temperature only

Question 5

What information shows if a reaction is exothermic or endothermic?

Answer 5

Reactions at equilibrium are shown with a value for H for the forward direction
- H indicates forward reaction is exothermic (and therefore reverse is endothermic)
+ H icates forward reaction is endothermic (and therefore reverse is exothermic)

Question 6

What is Le Chatelier principle?

Answer 6

For a reversible reaction in dynamic eqm, if a change is imposed in the system, the eqm will shift to oppose the change

Question 7

What happens to the position of an equilibrium if pressure is increased?

Answer 7

The equilibrium shifts to the side of the reaction with less number of gaseous moles

Question 8

What happens to the position of an equilibrium if temperature is increased?

Answer 8

The equilibrium shift to the endothermic direction to reduce temperature

Question 9

What happens to the position of an equilibrium if the concentration of a reactant is increased?

Answer 9

The equilibrium shifts to the products to remove the added reactants

Question 10

How does the addition of a catalyst affect a reaction at
equilibrium?

Answer 10

Does not affect the position of equilibrium, but speeds up the rate at which equilibrium is achieved

Question 11

Why does a catalyst not impact the yield?

Answer 11

increases the rate of forwards and reverse reactions equally

Question 12

Why are really high temperatures not always used even if they increase yield?

Answer 12

expensive

Question 13

Why is adding a catalyst to the equilibrium mixture useful?

Answer 13

• speeds up rate of forwards and backwards reactions
• allows lower temperature
• low temperatures are cheaper

Question 14

How could you check that a mixture had reached equilibrium after one week?

Answer 14

• test several samples at least one after one week
• check results dont change