A researcher investigates the thermal decomposition of solid ammonium nitrate

CHEMISTRY · Multi-part · A Level · Chemistry · Energetics · Energetics

Problem

A researcher investigates the thermal decomposition of solid ammonium nitrate, represented by the balanced chemical equation

\text{NH}_4\text{NO}_3(s) \longrightarrow \text{N}_2\text{O}(g) + 2\,\text{H}_2\text{O}(g)

The enthalpy change for the reaction as written is

\Delta H = +25.7\;\text{kJ\,mol}^{-1}

298\,\text{K}

and

1\,\text{atm}

. No numerical data about the amount of substance reacted are provided. (a) Identify whether the reaction is exothermic or endothermic and justify your answer by referring specifically to the sign of

\Delta H

. (b) Describe the mathematical relationship between the heat exchanged with the surroundings

(q)

and the amount of ammonium nitrate, in moles, that decomposes. Do not perform a numerical calculation. (c) Using your relationship from part (b), explain qualitatively how the quantity of heat absorbed would change if the number of moles decomposed were doubled. Include the expected sign of

q

in your explanation.

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