C6 Equilibrium

Question 1

What is Dynamic equilibrium?

Answer 1

The rate of the forward reaction is equal to the rate of the backwards reaction

Question 2

What is an essential condition for equilbrium to occur?

Answer 2

It can only occur in a closed system where reactants and products cannot escape

Question 3

State Le Chatelliers principle?

Answer 3

If a reaction at equilibrium is subjected to a change in pressure, temperature or concentration the position of equilibrium will shift to counteract the change

Question 4

State the reaction that produces ethanol

Answer 4

C2H4 (g) + H2O (g) ⇌ C2H5OH (g) ΔH = -46kj/mol-1

Question 5

What conditions are needed for the reaction of ethanol to occur?

Answer 5

Pressure at 60atmp
Temperature at 300 degrees celsius
Catalyst H3PO4

Question 6

In accordance to the reaction how can we change temperature to increase yield of ethanol?

Answer 6

We can increase yield of ethanol by decreasing the temperature as it would favour the exothermic reaction. The forward reaction is exothermic so more ethanol will be produced

Question 7

What is the compromise of using a low temperature like 300 degrees celsius for the reaction of ethanol?

Answer 7

lower temperature means a lower rate of reaction so 300 degrees is a compromise between yield and rate

Question 8

In accordance to the reaction how can we change pressure to increase yield of ethanol?

Answer 8

By increasing the pressure it will the favour the side with fewer number of moles to restablish equilibrium so more ethanol is produced increasing rate

Question 9

What is the compromise with using high pressure in reactions?

Answer 9

High pressure environments are expensive due to more expensive equipment needing to be used so a compromise is done between yield/speed and cost

Question 10

What effect does a catalyst have on the position of equilibrium?

Answer 10

No effect as it only speeds up the rate in which equilibrium is established

Question 11

What condition affects the value of Kc?

Answer 11

Temperature

Question 12

For the reaction below deduce an expression for Kc
2[A] + 3[B] + [C] ⇌ [D]+ 4[E]

Answer 12

Kc= [D][E]4/[A]2[B]3[C]

Question 13

What is the equation for Kc?

Answer 13

Kc= Products/reactants

Question 14

What type of system is Kc relevant for?

Answer 14

Homogeneous systems in equilibrium

Question 15

What effect does decreasing the temperature in an endothermic reaction have on Kc?

Answer 15

Kc decreases

Question 16

What effect does increasing the temperature in an endothermic reaction have on Kc?

Answer 16

Kc increases

Question 17

What effect does decreasing the temperature in an exothermic reaction have on Kc?

Answer 17

Kc increases

Question 18

What effect does increasing the temperature in an exothermic reaction have on Kc?

Answer 18

Kc decreases

Question 19

What does a catalyst do the forward and backward reaction?

Answer 19

Speeds up both the forward and backward reaction equally

Question 20

CH4( g) + H2O( g) ⇌ CO( g) + 3 H2( g) ΔH = +210KJj/mol-1
What effect would increasing the temperature have on the position of equilibrium?

Answer 20

The equilibrium position shifts to the right because the forward reaction is endothermic yield of hydrogen increases

Question 21

CH4( g) + H2O( g) ⇌ CO( g) + 3 H2( g) ΔH = +210KJj/mol-1
What effect would increasing the pressure have on the position of equilibrium?

Answer 21

The equilibrium position shifts to the left because the forward reactions produces more moles of gas so the yield of hydrogen increases

Question 22

CH4( g) + H2O( g) ⇌ CO( g) + 3 H2( g) ΔH = +210KJj/mol-1
Suggest and explain why an industrial chemist may use a high pressure for this production of hydrogen from above reaction?

Answer 22

The high pressure increase collision frequency increasing rate of reaction.
This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen