Exothermic and endothermic reactions

Question 1

The forward reaction is exothermic, so the reverse reaction is ________. [1]

Answer 1

endothermic

Question 2

Calculate the percentage by mass of nitrogen in ammonia (NH₃). [3]

Answer 2

82 (%)

Question 3

Suggest one improvement the student could make to the apparatus when investigating the temperature change. [2]

Answer 3

• add a lid…
• …to reduce / stop heat loss
• use a digital thermometer…
• …for more accurate data

Question 4

The reaction to produce magnesium from magnesium oxide is endothermic.
What is meant by an endothermic reaction? [1]

Answer 4

(a reaction which) takes in energy (from the surroundings)

Question 5

The equation for the reaction is:
2 NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g)
The cake mixture rises when baked.
Use the equation to suggest why. [1]

Answer 5

gas / carbon dioxide / steam is produced

Question 6

The same reaction can be reversed to produce sodium hydrogencarbonate from
sodium carbonate.
Na₂CO₃ + H₂O + CO₂ → 2NaHCO₃
Do the reactants need to be heated?
Give a reason for your answer. [1]

Answer 6

• no, because (reaction) is exothermic

- yes, to start the reaction