3.1.6 Equilibria

Question 1

All reversible reactions reach a _____/_____ state

Answer 1

All reversible reactions reach a dynamic equilibrium state

Question 2

If the number of moles of gas is the same on both sides of a reversible reaction, pressure ____/_____/__/_____/__/___/_____/__/________

Answer 2

If the number of moles of gas is the same on both sides of a reversible reaction, pressure will have no effect on the position of equilibrium.

Question 3

The _____ the Kc the _______ the amount of products

Answer 3

The larger the Kc the greater the amount of products

Question 4

What is the only external condition that affects value of Kc?

Answer 4

Temperature

Question 5

How does temperature affect the value of Kc?

Answer 5

-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 6

What does the term dynamic mean in dynamic equilibrium?

Answer 6

Both forward and backward reactions are occuring simultaenously

Question 7

What are two features of dynamic equilibrium?

Answer 7

1. Forward and backward reactions occuring at equal rates
2. Concentrations of both reactants and products remain constant

Question 8

What does Le Chatelier’s principle state?

Answer 8

If an external condition is changed, equilibrium will shift to oppose the change.

Question 9

What is the effect of increasing temperature on equilibrium?

Answer 9

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

Question 10

What is the effect of decreasing temperature on equilibrium?

Answer 10

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

Question 11

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

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Answer 11

-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 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 13

What is the effect of increasing pressure on equilibrium?

Answer 13

-equilibrium shifts to the side with fewer moles
-to oppose the change and thereby reducing pressure

Question 14

What is the effect of decreasing pressure on equilibrium?

Answer 14

-equilibrium shifts to the side with more moles
-to oppose the change and thereby increase pressure

Question 15

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

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Answer 15

-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 16

What are the drawbacks of using high pressures in industry?

Answer 16

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

Question 17

What is the effect of increasing concentration on equilibrium?

Answer 17

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

Question 18

What is the effect of decreasing concentration on equilibrium?

Answer 18

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

Question 19

What is the effect of catalysts on equilibrium?

Answer 19

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

Question 20

How do you work out the equilibrium constant?

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Answer 20

GOOGLE DOC

Question 21

How do you work out the unit of Kc?

Answer 21

Units will change depending on the equation that is formed. Write each individual unit and see what it cancels to.

Question 22

Define the term ‘catalyst’ and explain how a catalyst works: MS [3]

Answer 22

A substance that speeds up the reaction, but is chemically unchanged at the end (not used up)

They work by providing an alternative reaction pathway
With lower activation energy

Question 23

Give the meaning of the term activation energy: MS [2]

Answer 23

The activation energy is the minimum amount of energy
needed for a reaction to occur with successful collisions

Question 24

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

Answer 24

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 25

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

Answer 25

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

Question 26

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

Answer 26

The molecules of the gases must collide

With at least the activation energy

Question 27

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

Answer 27

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