reversible reactions and equilibria

Question 1

name 2 reversible reactions

Answer 1

1. the dehydration of hydrated copper(II) sulfate

2. the heating of ammonium chloride

Question 2

describe the dehydration of hydrated copper (II) sulphate.

Answer 2

• before heating, blue solids of copper (II) sulphate.
• during heating, steam comes out of the boiling tube
• after heating, there is a white powder.
• when water is added again, blue solids form again.

Question 3

give the symbol equation for the dehydration of copper (II) sulphate.

Answer 3

CuSO4.5H2O (s) <=> CuSO4 (s) + 5H2O (g)

Question 4

describe the heating of ammonium chloride.

Answer 4

• before heating, there is a white solid.
• during heating, a white pungent gas (ammonia) is produced.
• after heating, the white solid is reformed at the top of the tube

Question 5

give the symbol equation for the heating of ammonium chloride.

Answer 5

NH4Cl (s) <=> NH3 (g) + HCl (g)

Question 6

what type of reaction is the heating of ammonium chloride?

Answer 6

thermal decomposition.

Question 7

give a test you could do to confirm the presence of ammonia.

Answer 7

damp red litmus paper turns blue

Question 8

what is the purpose of mineral wool in the heating of ammonium chloride.

Answer 8

to prevent the ammonium chloride from escaping.

Question 9

describe equilibrium

Answer 9

if a reversible reaction takes place in a closed system, a state of equilibrium will always be reached.

Question 10

what is meant by a closed system?

Answer 10

one from which reactants and products can’t escape from.

Question 11

what is meant by equilibrium?

Answer 11

when:

• the forward and reverse reactions occur at the same rate
• the concentrations of reactants and products remain constant.

Question 12

give three ways to alter the position of equilibrium

Answer 12

• change the concentration of reactants/products
• change the pressure
• change the temperature

Question 13

state the effect of altering concentration on the position of equilibrium.

Answer 13

changing the concentration of a reactant or product will push the equilibrium in the direction that opposes the change made.

Question 14

if the concentration of a reactant is increased the equilibrium moves to the —-

Answer 14

right (forward reaction is favoured)

Question 15

if the concentration of a reactant is decreased the equilibrium moves to the —-

Answer 15

left (reverse reaction is favoured)

Question 16

give the effect of changing temperature on equilibrium.

Answer 16

increasing temperature pushes the equilibrium in the endothermic direction.
decreasing temperature pushes the equilibrium in the exothermic direction.

Question 17

if DELTAH = -ve, what time of reaction is the forward reaction?

Answer 17

exothermic

Question 18

if DELTAH = +ve, what time of reaction is the forward reaction?

Answer 18

endothermic

Question 19

state the effect of altering pressure on equilibrium.

Answer 19

increasing pressure pushes equilibrium in the direction of fewer moles of gas.
decreasing pressure pushes equilibrium in the direction of more moles of gas.

Question 20

why does the addition of a catalyst not change the position of equilibrium?

Answer 20

a catalyst provides an alternative pathway requiring lower activation energy for both forward and backward reactions, therefore increasing the rate of forward and backward reaction by the same amount