Equilibrium

Question 1

Reversible reactions

Answer 1

Reactions which can go both ways, ie the reactants can make products and products can make reactants

Question 2

How are reversible reactions represented?

Answer 2

With a double arrow, half an arrow head on each one

Question 3

What is dynamic equilibrium?

Answer 3

When the forward and backward reactions occur at the same rate
So concentration of reactants and products remain the same

Question 4

Important aspects of equilibrium

Answer 4

Can only occur in closed systems
The reactions are still occurring, the rate at which reactants/products are made is equal so no visible change appeared

Question 5

How is dynamic equilibrium achieved?

Answer 5

Reactants react in forward reaction and get used up (slows down) more product formed
Backwards reaction speeds up to form more products as a result
So eventually these reactions at same rate

Question 6

Le Chateliers principle

Answer 6

When a system under dynamic equilibrium is changed, the position of equilibrium shifts to counteract the change

Question 7

What factors can be changed to shift the position of equilibrium?

Answer 7

Concentration of either reactant or product
Temperature
Pressure (gases only)

Question 8

Why does imposing changes on a system cause the position of equilibrium to shift?

Answer 8

Imposing a change would effect the dynamic equilibrium so the system changes the position of equilibrium to counteract the change eg lowering temp, lowering pressure or concentration

Question 9

Endothermic and exothermic reversible reactions

Answer 9

One direction will be endothermic and the other direction is exothermic

Question 10

When given a value of an energy change in a reaction, what is important?

Answer 10

The energy change value is for the foreword reaction

Question 11

Endothermic energy values

Answer 11

Positive number (energy taken in)

Question 12

Exothermic energy values

Answer 12

Negative number (energy released)

Question 13

Increasing the temperature of a system means you give… to the system?

Answer 13

Heat is given to system

Question 14

Effect of increasing temperature on dynamic equilibrium?

Answer 14

The equilibrium shifts to the endothermic direction so energy is taken in to counteract the increase in heat energy

Question 15

What happens to the yield when you increase the temperature of a system?

Answer 15

You increase the yield of the products of the endothermic reaction

Question 16

Decreasing the temperatures takes away… of a system in dynamic equilibrium?

Answer 16

Heat

Question 17

Effect of decreasing temperature on dynamic equilibrium?

Answer 17

The equilibrium shifts to the exothermic reaction because heat was taken away so more heat released to counteract the heat that had been taken away

Question 18

What happens to the yield when you decrease the temperature of a system?

Answer 18

You increase the products of the exothermic reaction

Question 19

Increase in pressure does what to a system?

Answer 19

Decrease the volumes so there are more gas molecules in a given volume

Question 20

Decrease in pressure does what to a system?

Answer 20

Increases the volume so there are less gas molecules in a given volume

Question 21

What do changes in pressure refer to?

Answer 21

Only when all products/reactants are gases

Question 22

What happens when you increase the pressure of gaseous chemicals in equilibrium

Answer 22

The equilibrium shifts to the side with fewer gaseous molecules to counteract the change and produce a higher concentration of the side with less molecules as shown by stoichiometry

Question 23

What happens when you decrease the pressure of gaseous chemicals in equilibrium?

Answer 23

Equilibrium shifts to the side with more gaseous molecules to counteract the decrease by producing more reactants which have more gas molecules
According to stoichiometry

Question 24

What happens if you increase the concentration of a reactant

Answer 24

The position of equilibrium shifts of the opposite direction (make more of the other reactant which was increased)

Question 25

What happens if you decrease the concentration of a reactant?

Answer 25

The position of equilibrium shifts to the opposite direction (which makes more reactant) to oppose the decrease in concentration and form more reactants

Question 26

How do catalysts effect a reversible reaction in dynamic equilibrium?

Answer 26

Increases the rate of both the forward and backward reaction
No effect on the yield because the catalyst increases the rate of BOTH reactions

Question 27

What does position of equilibrium tells us?

Answer 27

The composition of the reaction mixture due to which reaction is favoured

Question 28

Do catalysts have any effect on position of equilibrium?

Answer 28

No, they increase the rate of reaction equally on both sides so the rate changes on both sides (increases speed to achieve equilibrium) thus the position of equilibrium does not change

Question 29

Why do we use catalysts in industrial processes?

Answer 29

So we can increases the rate of reaction while having a low temperature thus lower energy costs

Question 30

Why do we use catalysts in industrial processes?

Answer 30

So we can increases the rate of reaction while having a low temperature thus lower energy costs

Question 31

Industry: using high temperatures problem

Answer 31

High energy costs

Question 32

Industry: high pressures problem

Answer 32

High cost to keep pumps which maintain the high pressure of gaseous molecules

Question 33

What is one way to improve yield of reversible reactions in industry?

Answer 33

Recycle the reactants back