reversible reactions

Which reaction is reversible?

• Cu + ZnSO₄ → CuSO₄ + Zn

• CuO + H₂SO₄ → CuSO₄ + H₂O

• CuO + H₂ → Cu + H₂O

• CuSO₄.5H₂O → CuSO₄ + 5H₂O

Answer explanation

eqn 1 - is displacement

eqn 2 - salt preparation

eqn 3 - reduction of copper oxide(loss of oxygen)

Which reaction is not a reversible reaction?

• combustion of fuel

• hydration of anhydrous copper(II) sulfate

• melting lead(II) bromide

• thermal decomposition of hydrated cobalt(II) chloride

Answer explanation

combustion of fuel produces carbon dioxide and water which cannot be reversed.

The diagram shows the change from an anhydrous salt to its hydrated form.Which statement is correct?

• forward reaction requires heat and water

• forward reaction requires water only

• reverse reaction requires heat and water

• reverse reaction requires water only

Answer explanation

anhydrous means no water and hydrated means water present.

The equation shows a reaction that is reversed by changing the conditions. How can the forward reaction be reversed?

• by adding water and then heating

• by adding water

• by heating

• none of them

Answer explanation

forward reaction is losing water therefore reverse reaction is done by adding water

When hydrated green iron(II) sulfate is heated, it turns white and a colourless liquid is produced. When the liquid is put back into the white solid it changes back to green. What type of reaction takes place and what is the name of the liquid?

• redox/ sulfuric acid

• redox/ water

• reversible/ sulfuric acid

• reversible/ water

Answer explanation

it is a reversible reaction and the colourless water is liquid

Heating pink cobalt(II) chloride crystals forms a blue solid and steam. The blue solid turns pink when water is added. Which terms describe the pink cobalt(II) chloride and the reaction?

• anhydrous and reversible

• anhydrous and irreversible

• hydrated and reversible

• hydrated and irreversible

The reversible sign is used in some equations to show that a reaction is reversible. Two incomplete equations are given. For which of these reactions reversible sign be correctly used to complete the equation?

• P & Q

• P only

• Q only

• neither P or Q

Answer explanation

adding water and removing water is a reversible reaction

The equation for the effect of heat on hydrated sodium carbonate is as shown.

Statements made by four students about the reaction are given.

P- Anhydrous sodium carbonate is formed.

Q- Steam is formed.

R- There is a colour change from blue to white.

S- The reaction is reversible.

Which students’ statements are correct?

• P, Q and R only

• P, Q and S only

• Q, R and S only

• P, Q, R and S

Answer explanation

Group 1 metal salts are coulourless therefore no colour change will take place.

When pink crystals of cobalt(II) chloride are heated, steam is given off and the colour of the solid changes to blue.

What happens when water is added to the blue solid?

• changes to pink and temperature decreases

• changes to pink and temperature increases

• remains blue and temperature decreases

• remains blue and temperature increases

When blue copper(II) sulfate is heated, a white solid and water are formed. The white solid turns blue and gives out heat when water is added to it. Which terms describe the blue copper(II) sulfate and the reactions?

• the blue copper(II) sulfate is a mixture and reaction can be reversed

• the blue copper(II) sulfate is a mixture and reaction cannot be reversed

• the blue copper(II) sulfate is hydrated and reaction can be reversed

• the blue copper(II) sulfate is hydrated and reaction cannot be reversed