Equilibrium I

Question 1

What is a reversible reaction?

Answer 1

Is one that goes in both directions at the same temperature

Question 2

What is meant by term equilibrium?

Answer 2

A system is in equilibrium when there is no further change in the concentrations of the reactants and products

Question 3

what happens in a dynamic equilibrium?

Answer 3

in a dynamic equilibrium, the rates of the forward and reverse reaction are equal. Therefore there is no further change in the concentrations of the reactants and products

Question 4

What is le Chatelier’s principle?

Answer 4

when the conditions of a system in equilibrium is alters in such a way as to try to restore the original conditions

Question 5

what happens if a system at equilibrium is heated?

Answer 5

the temperature rises and the system reacts to remove the heat energy and bring the temperature down.
This means that heat energy must be converted to chemical energy

Question 6

Where does an increase in temperature shift equilibrium ?

Answer 6

to the endothermic side

Question 7

What happens when temperature shifts in the endothermic direction?

Answer 7

a decrease in the equilibrium yield for an exothermic reaction
An increase in the equilibrium yield for the endothermic reaction

Question 8

When temperature decreases what happens to the energy?

Answer 8

the chemical energy is converted to heat energy , restoring the temperature

Question 9

why does an increase in temperature speed up the endothermic reactions in the equilibrium more than the exothermic?

Answer 9

This is because the Ea for the reaction on endothermic is greater than that for the reaction in the exothermic direction. The reaction with high Ea are more sensitive to temperature changes than reactions with lower Ea

Question 10

When does the effect of pressure apply to in equilibrium?

Answer 10

only applies to equilibrium reactions involving gases

Question 11

What is pressure caused by?

Answer 11

pressure is caused by the bombardment of the gas molecules on the walls of the container

Question 12

At a given temperature, what does the pressure depend on?

Answer 12

only on the number of gas molecules in a given volume

Question 13

What is the pressure of an equilibrium system increased by?

Answer 13

reducing the volume or
adding more gas into the same volume
Results in more molecules per cm^3

Question 14

If the pressure is increased, according to le chatelier’s principle what will happen?

Answer 14

That the system will react in order to try to bring the pressure down again towards the original value. This can only happen if equilibrium shifts to the direction with fewer gas molecules

Question 15

A decrease in pressure will result in what?

Answer 15

the equilibrium shifting towards the side of the equation with more gas molecules.

Question 16

When does the effect of equilibrium apply to a system?

Answer 16

It applies to a system in which the reactants are dissolved in a solvent, usually water

Question 17

What happens if the concentration of one of the substances in the equilibrium reaction is increased according to le chatelier’s?

Answer 17

position will shift to remove some of that substances

Question 18

What happens to equilibrium if the concentration of one of the species is decreased?

Answer 18

the position will shift to produce more of that species

Question 19

How does a catalyst work?

Answer 19

By providing an alternative route that has a lower Ea than that of an uncatalysed reaction. Faster ROR

Question 20

How does a catalyst affect the position of equilibrium?

Answer 20

has no effect on the position of equilibrium but it will speed up the rate at which the
equilibrium is achieved.

Question 21

Why are catalysts important in industrial processes?

Answer 21

As many reactions are extremely slow at room temperature

Question 22

How can the overall yield of industrial processes be improved?

Answer 22

Recycling unreacted reactants back into the reactor can improve the overall yields of all these processes

Question 23

Give 4 examples of industrial processes using the concept of equilibrium

Answer 23

Haber process
Contact process
Production of methanol from CO
Hydration of ethene to produce ethanol

Question 24

key details of haber process

Answer 24

N2 + 3H2 2NH3 H = -ve exo
T= 450oC, P= 200 – 1000 atm, catalyst = iron
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

Question 25

key details of production of methanol from CO

Answer 25

CO (g) + 2H2(g) CH3OH (g) H = -ve exo T= 400oC, P= 50 atm, catalyst = chromium and
zinc oxides
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

Question 26

key details of the contact process

Answer 26

Stage 1 S (s) + O2 (g)SO2 (g)
Stage 2 SO2 (g) +1⁄2O2 (g) SO3 (g) H = -98 kJ mol-1
T= 450oC, P= 1 to 2 atm, catalyst = V2O5
Low temp gives good yield but slow rate: compromise moderate temp used
High pressure gives slightly better yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

Question 27

key details of hydration of ethene to produce ethanol

Answer 27

CH2=CH2 (g) + H2O (g) CH3CH2OH(l) H = -ve
T= 300oC, P= 70 atm, catalyst = conc H3PO4
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
High pressure also leads to unwanted polymerisation of ethene to poly(ethene)

Question 28

what does kc stand for?

Answer 28

equilibrium constant

Question 29

how do you work out kc

Answer 29

products over reactants , moles become powers