A constant-pressure calorimetry investigation is performed on the generic exothermic…

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

Problem

A constant-pressure calorimetry investigation is performed on the generic exothermic reaction

\mathrm{A + 2B \longrightarrow C} \qquad \Delta H = -100\;\text{kJ\,mol}^{-1}\text{ (per mole of reaction as written)}.

Two separate trials are carried out under identical conditions. • Trial 1 starts with

0.50\,\text{mol}\;\mathrm A

and

1.0\,\text{mol}\;\mathrm B

. • Trial 2 starts with

0.50\,\text{mol}\;\mathrm A

and

2.0\,\text{mol}\;\mathrm B

. For each trial the calorimeter records the heat exchanged with the surroundings (

q_{\text{cal}}

). Respond to the following prompts. (a) Describe qualitatively how the magnitude of

q_{\text{cal}}

depends on which reactant is limiting in a constant-pressure calorimetry experiment. (b) For the two trials described, predict which trial will release the greater magnitude of heat to the surroundings. Justify your answer without performing numerical calculations. (c) For an endothermic reaction of the same scale, state and explain the sign convention for

q

of (i) the system and (ii) the surroundings.

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