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 equilibrium?

Answer 3

When in a reversible reaction, there is no net change in the amount of product or reactant

Question 4

What is dynamic equilibrium?

Answer 4

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

Question 5

Important aspects of equilibrium

Answer 5

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 6

How is dynamic equilibrium achieved?

Answer 6

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 7

Le Chateliers principle

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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 10

Endothermic and exothermic reversible reactions

Answer 10

One direction will be endothermic and the other direction is exothermic

Question 11

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

Answer 11

The energy change value is for the foreword reaction

Question 12

Endothermic energy values

Answer 12

Positive number (energy taken in)

Question 13

Exothermic energy values

Answer 13

Negative number (energy released)

Question 14

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

Answer 14

Heat is given to system

Question 15

Effect of increasing temperature on dynamic equilibrium?

Answer 15

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

Question 16

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

Answer 16

You increase the yield of the products of the endothermic reaction

Question 17

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

Answer 17

Heat

Question 18

Effect of decreasing temperature on dynamic equilibrium?

Answer 18

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 19

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

Answer 19

You increase the products of the exothermic reaction

Question 20

Increase in pressure does what to a system?

Answer 20

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

Question 21

Decrease in pressure does what to a system?

Answer 21

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

Question 22

What do changes in pressure refer to?

Answer 22

Only when all products/reactants are gases

Question 23

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

Answer 23

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 24

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

Answer 24

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 25

What happens if you increase the concentration of a reactant

Answer 25

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

Question 26

What happens if you decrease the concentration of a reactant?

Answer 26

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

Question 27

How do catalysts effect a reversible reaction in dynamic equilibrium?

Answer 27

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