A strip of pure magnesium metal reacts with excess aqueous HCl according to the…

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

Problem

A strip of pure magnesium metal reacts with excess aqueous HCl according to the balanced chemical equation

\text{Mg}(s)+2\,\text{HCl}(aq)\;\longrightarrow\;\text{MgCl}_{2}(aq)+\text{H}_{2}(g)

For laboratory convenience, the enthalpy change for this reaction is supplied as an intensive value of

\Delta H = -0.742\,\text{kJ g}^{-1}

of Mg consumed at the specified temperature. A student places a

2.35\,\text{g}

strip of Mg into excess

\text{HCl}

in a perfectly insulated calorimeter. (a) Calculate the heat

q

(in kilojoules) released when the entire strip reacts. (b) Convert the given intensive enthalpy change to a molar enthalpy change (

\text{kJ mol}^{-1}

). Show your reasoning. (c) Justify whether the sign of

q

calculated in part (a) is consistent with the classification of the reaction as endothermic or exothermic.