Equilibria

Question 1

Le Chatelier’s principle states that

Answer 1

Le Chatelier’s principle states that when a change is imposed on an equilibrium, the equilibrium position will shift to oppose the change.

Question 2

The change Le Chatelier refers to can be as a result of:

Answer 2

The change Le Chatelier refers to can be as a result of:
Change in temperature.
Change in pressure.
Change in concentration.

Question 3

What happens when an exothermic reversible reaction is cooled down?
1
Decide which way releases heat

2
Decide which reaction increases

3
Decide where the equilibrium position goes

Answer 3

What happens when an exothermic reversible reaction is cooled down?
1
Decide which way releases heat
The forward reaction releases heat in this example
2
Decide which reaction increases
You want more heat, so the rate of the forward reaction increases
3
Decide where the equilibrium position goes
It shifts to the right because more products are formed by a faster forwards reaction

Question 4

At equilibrium, both forward and backward reactions still happen, but the ..
So we describe the equilibrium as

Answer 4

At equilibrium, both forward and backward reactions still happen, but the concentrations of reactants and products remain constant. So we describe the equilibrium as dynamic

Question 5

What are the conditions used in the synthesis of ethanol?

Answer 5

300° c

65 atm

Question 6

n equilibrium constant greater than one indicates that

An equilibrium constant less than one indicates that

Answer 6

n equilibrium constant greater than one indicates that the forward reaction dominates.
An equilibrium constant less than one indicates that the backward reaction dominates.

Question 7

Whats dynamic equilibrium

Answer 7

At dynamic equilibrium concentrations of reactants and products are constant and the forwards reaction in the backwards reaction are going at the same rate

Question 8

What conditions are needed for dynamic equilibrium to be established

Answer 8

For a dynamic equilibrium to be established it must be a closed system and the temperature must be constant

Question 9

How does the addition of a catalyst affect the position of equilibrium in a reversible reaction

Answer 9

The addition of a catalyst has no affect on the position of the equilibrium in a reversible reaction

Question 10

An industrial process uses the following reversible reaction

A + 2B (reverse signs) C + D

Change in enthalpy = -189Kjmol-1

Explain the effect of increasing the concentration of a on the position of equilibrium

Answer 10

Shift the equilibrium to the right favouring the forward reaction in order to get rid of the EXcess a

Question 11

An industrial process uses the following reversible reaction

A + 2B (reverse signs) C + D

Change in enthalpy = -189Kjmol-1

Explain the effect of increasing the pressure on the position of equilibrium

Answer 11

There are three moles on the left and only two on the right increasing the pressure will shift the equilibrium to the right in order to reduce the number of moles to reduce the pressure again

Question 12

An industrial process uses the following reversible reaction

A + 2B (reverse signs) C + D

Change in enthalpy = -189Kjmol-1

Explain the effect of increasing the temperature on the position of equilibrium

Answer 12

The fourth reaction is exothermic so the backwards reaction must be endothermic increasing the temperature will shift the equilibrium to the left in order to remove the extra heat

Question 13

What will be the effect of increasing the pressure on the position of equilibrium of the following reaction they both have two molecules on either side of the reaction

Answer 13

There are the same number of moles on either side of the reaction increase increasing the pressure favours the reaction producing the fewest moles but since both reactions are equal in this respect increasing the pressure will not shift the position of equilibrium

Question 14

In the production of ethanol from Ethene and steam using low temperature and high-pressure favours the forward reaction and gives a better yield

given that this is the case explain why a moderate temperature and pressure are used when making ethanol and Industrially

Answer 14

The temperature and pressure used in the industrial production of ethanol or a compromise

using a low temperature increases the yield of the reaction
but at a low temperature of the reaction rate becomes much slower so moderate temperature is used as a compromise

between a good yield and a fast reaction using a high-pressure also increases the yield of the reaction but high pressures are expensive to produce you need stronger pipes and containers to withstand high pressure so moderate pressure is used as compromise between maximum yield and minimum expense

Question 15

Why does changing the concentration of a reagents doesn’t affect Kc

Answer 15

If the concentration of a reagent is changed equilibrium will shift and the concentration of other reagents will also change so Kc will stay the same

Question 16

How does adding a catalyst affect the equilibrium constant

Answer 16

Doesn’t change Kc but it decreases the time taken to reach equilibrium

Question 17

What is petroleum

Answer 17

A mixture that consists mainly of alkane hydrocarbons

Question 18

Why are alkanes described as saturated hydrocarbons

Answer 18

they only contain carbon and hydrogen atoms

each of the carbon is forms four single bonds they are no carbon carbon double bonds present

Question 19

Fractional distillation separates hydrocarbons what property are they separated by

Answer 19

Boiling point

Question 20

Explain why some fractions are drawn off higher up the fractional distillation column than others

Answer 20

Some fractions have lower boiling points than others this means they can dance further up the columns so are drawn off higher up

Question 21

What is cracking

Answer 21

Cracking is breaking long chain alkanes into smaller hydrocarbons

Question 22

Why do we crack heavier petroleum fractions

Answer 22

There is more demand for later petroleum factions Sol to meet the demand the heavier fractions are cracked into lighter fractions

Question 23

Why does using a catalyst for catalytic cracking cut costs

Answer 23

Because the reaction can be done at a lower temperature and pressure and at an increased speed

Question 24

Write the equation for the complete combustion of pentane

Answer 24

Cnnc

Question 25

Give three pollutants produced by vehicle exhausts

Answer 25

Nitrogen oxides carbon monoxide soot unburnedhydrocarbons carbon dioxide

Question 26

What can be used to remove pollutants from vehicle exhausts

Answer 26

Catalytic converter

Question 27

Explain how acid rain is caused by burning fossil fuels containing sulphurz

Answer 27

The sulphur burns to produce sulphur dioxide gas

if sulphur dioxide gas enters the atmosphere it can dissolve in the moisture and form sulphuric acid

Question 28

Describe one method for removing sulphur dioxide from fluegases

Answer 28

Powdered calcium carbonate can be mixed with water to make an alkaline slurry
when the fluegases mix with the alkaline slurry that acidic sulphur dioxide gas reacts with the calcium compounds to form a harmless salt

Question 29

What’s a photochemical reaction

Answer 29

U

Question 30

Write an equation for the initiation step of the synthesis of chloromethane by photochemical reaction

Answer 30

G

Question 31

Describe what takes place in the termination step of a free radical substitution mechanism

Answer 31

G

Question 32

Why is ozone in the atmosphere beneficial

Answer 32

H

Question 33

Describe how chlorine free radicals are formed in the upper atmosphere

Answer 33

T

Question 34

Right to equations to show how chlorine atoms catalyse the decomposition of ozone

Answer 34

Y

Question 35

Explain why CFCs were banned from use as solvents and refrigerants

Answer 35

G