A student mixes a strip of magnesium metal with aqueous hydrochloric acid at constant…

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

Problem

A student mixes a strip of magnesium metal with aqueous hydrochloric acid at constant pressure in an open Styrofoam calorimeter. Chemical equation (standard conditions):

\mathrm{Mg(s) + 2\,HCl(aq) \longrightarrow MgCl_2(aq) + H_2(g)} \qquad \Delta H = -152\;\text{kJ\,mol}^{-1}\text{ (per mole of reaction as written)}

The reactants are provided as follows: • Mass of Mg(s):

2.40\,\text{g}

(molar mass

24.3\,\text{g\,mol}^{-1}

) • Volume of

1.50\,\text{M}

HCl(aq):

150.\,\text{mL}

Assume the following for the calorimetric system. • Density of the final solution:

1.00\,\text{g\,mL}^{-1}

• Specific heat capacity of the solution:

4.18\,\text{J\,g}^{-1}\,^{\circ}\text{C}^{-1}

• No heat is lost to the calorimeter or the surroundings. Answer the following questions. (a) Calculate the initial amount (in moles) of each reactant present in the calorimeter. (b) Identify the limiting reactant for the process. (c) Determine the quantity of heat

q

(in kilojoules) released or absorbed by the reaction in the calorimeter. Indicate the sign of

q

for the system. (d) Calculate the temperature change

\Delta T

(in

^{\circ}\text{C}

) experienced by the solution as a result of the reaction.

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