Four separate samples undergo the same chemical process

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

Problem

Four separate samples undergo the same chemical process, but with different amounts of reactant. The molar enthalpy change for the process under the experimental conditions is

\Delta H = -135\,\text{kJ}\,\text{mol}^{-1}

. Trial data: Trial A:

0.250\,\text{mol}

Trial B:

1.20\,\text{mol}

Trial C:

0.800\,\text{mol}

Trial D:

1.00\,\text{mol}

(a) For each trial, calculate the quantity of heat

q

(in

\text{kJ}

) exchanged with the surroundings. Indicate the sign of

q

. (b) Rank the four trials from the one that releases the greatest amount of heat to the one that releases the least. Clearly state your ranking and support it with the calculated values. (c) If the same process were carried out using

0.500\,\text{mol}

of reactant but under conditions where

\Delta H

became

-128\,\text{kJ}\,\text{mol}^{-1}

, predict whether the heat released would be greater than, equal to, or less than that in Trial C. Justify your prediction quantitatively.

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