Kc

Question 1

How does temperature affect the value of Kc?

Answer 1

• temperature will cause a shift in the position of equilibrium
• if eq. shifts to the right, Kc will increase as there are more products
• if eq. shifts to the left, Kc will decrease as there are less products

Question 2

The … the Kc the … the amount of products

Answer 2

Larger
Greater

Question 3

Explain why a small increase in temperature has a large effect on the initial rate of a reaction: MS [1]

Answer 3

A small increase in temperature will cause many more molecules to have at least the activation energy

Question 4

Explain what must happen for a reaction to occur between molecules of two different gases: MS [2]

Answer 4

The molecules of the gases must collide

With at least the activation energy

Question 5

State and explain the effect of an increase in total pressure on the rate of attainment of an equilibrium: MS [3]

Answer 5

• Increased rate of equilibrium achievement
• More particles will be present in a given space
• More successful collisions will occur

Question 6

With reference to a Maxwell–Boltzmann distribution, explain why an increase in temperature increases the rate of a chemical reaction: MS [4]

Answer 6

• The peak of the curve will be displaced to the right
• The peak will be lower than the original curve
• Particles have more kinetic energy, hence more collisions occure
• More particles have energies greater than or equal to Ea

Question 7

What is the effect of catalysts on equilibrium?

Answer 7

no effect on position of equilibrium
speeds up the rate at which equilibrium is achieved

Question 8

What is the effect of decreasing concentration on equilibrium?

Answer 8

equilibrium shifts to oppose this change
moves in direction to remove and increase the concentration of the substance removed

Question 9

What is the effect of increasing concentration on equilibrium?

Answer 9

equilibrium shifts to oppose this change
moves in direction to remove and decrease the concentration of the substance added

Question 10

What are the drawbacks of using high pressures in industry?

Answer 10

high electrical energy costs for pumping gases to maintain high pressure
equipment is expensive

Question 11

What effect would increasing pressure have on the yield of methanol?

CO + 2H2 <—> CH3OH

Answer 11

• equilibrium shifts to oppose the increase in pressure, moving to the side with fewer gas molecules
• position of equilibrium shifts to the right because there are 3 moles on the left but only one on the right
• resulting in a higher yield of methanol

Question 12

What’s the issue surrounding equilibrium if the forward reaction is exothermic? How is this overcome?

Answer 12

• decreasing temperature would shift equilibrium to the right
• however; it would lower the rate of reaction (rate of attainment of equilibrium)
• a compromsie temperature is used that gives a reasonable yield and rate

Question 14

What effect would increasing temperature have on the yield of Ammonia? (4m)

N2 + 3H2 <—> 2NH3 -ve

Answer 14

• shifts in the endothermic direction
• backwards reaction is favoured to try and decrease temperature
  position of equilibrium shifts to the left
• lower yield of ammonia

Question 15

What is the effect of decreasing temperature on equilibrium?

Answer 15

• equilibrium shifts in the exothermic direction
• tries to increase temperature by giving out heat

Question 16

What is the effect of increasing temperature on equilibrium?

Answer 16

equilibrium shifts in the endothermic direction
tries to reduce temperature by absorbing heat