Chemical Equilibrium

Question 1

What is Chemical Equilibrium?

Answer 1

Chemical equilibrium is the state in which the rate of the forward reaction equals the rate of the reverse reaction

Question 2

What is the formula for Kc?

Answer 2

[products]^moles / [Reactants]^moles

Note: In the cases of numerous products/Reactants., use the exponent on each one and then add them

Question 3

What does the value of Kc depend on at equilibrium?

Answer 3

Temperature

Question 4

Why is chemical equilibrium dynamic?

Answer 4

Chemical equilibrium is dynamic as the forward and reverse reactions are continuously occurring

Question 5

What happens Kc if the forward reaction is exothermic and the temperature increases

Answer 5

It decreases

Question 6

What happens Kc if the forward reaction is endothermic and the temperature increases

Answer 6

It increases

Question 7

What is Le Chatelier’s principle

Answer 7

When a system at equilibrium is subjected to stress, the equilibrium shifts in such a way to minimise the effect of stress.

Question 8

What happens to a reaction at equilibrium if there is a change in concentration of one species

Answer 8

• If the species concentration decreases, the reaction that produces more of that species is favoured
• If the species concentration increases, the reaction that uses the that species as a reactant is favoured

Question 9

What happens to a reaction at equilibrium, if the temperature is changed?

Answer 9

• If the temperature increases, the reaction that is endothermic is favoured
• If the temperature decreases, the reaction that is exothermic is favoured

Question 10

What happens to a reaction at equilibrium, if a catalyst is added?

Answer 10

Nothing. The catalyst spped up the forward and reverse reaction equally

Question 11

What happens to a gas reaction at equilibrium, if the pressure changes?

Answer 11

• If the pressure increases, the reaction(if there is one) that produces less molecules will be favoured
• If the pressure decreases, the reaction(if there is one) produces more molecules is favoured

Question 12

What is the process, ammonia synthesis more commonly called?

Answer 12

The Haber process

Question 13

What is the ammonia synthesis equation?

Answer 13

N₂ + 3H₂ 2NH₃

Question 14

At what temperature does the Haber process take place?

Answer 14

As the forward reaction is exothermic, a low temperature would be efficent, however to keep the rate of reaction high, the temperature is 673K.

Question 15

At what pressure does the Haber process take place?

Answer 15

As the product of the forward reaction contsists of two moles while the reactants consists four moles, an increase of pressure would favour the forward reaction.

As a result, the Haber process occurs at 200 atms

Question 16

What catalyst is used in the Haber process?

Answer 16

Iron based catalysts ( Fe₂ Fe₃, Fe₂O etc)

Question 17

What is the process of making sulfur trioxide called?

Answer 17

The Contact process

Question 18

What is the equation for the Contact process reaction?

Answer 18

SO₂ + 1/2O₂ SO₃

Question 19

At what temperature does the Contact process take place

Answer 19

The forward reaction is exothermic, so a low temperature would increase the productoin of sulfur trioxide. However, to keep the rate of reaction relatively high, a temperature of 713K is used

Question 20

What pressure does the Contact process occur at?

Answer 20

As only 1 mole is produced and 3/2 moles react in the forward reaction, a higher pressure would favour the forward reaction. However, only a pressure of about 1 atm is used. A good enough yield is produced at this pressure and higher pressures can not be economically justified.

Question 21

What happen with regard to the concentration of Sulfur trioxide as the Contact process reaction occurs?

Answer 21

The sulfur trioxide is removed, thus the foward reaction which produces sulfur trioxide is favoured and more sulfur trioxide is produced.

Question 22

What catalyst is used in the Contact process?

Answer 22

Vandium Pentoxide ( VO₅)

Question 23

Why are industrial reactions such as the Haber process and the Contact process not allowed to reach equilibrium?

Answer 23

As a reaction gets closer to equilibrium, the rate of increase in yield slows down. It is not economical in industry to wait for maximium yield of the reaction