Hydrogen gas reacts vigorously with fluorine gas to produce hydrogen fluoride: H _ 2…

CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance

Problem

Hydrogen gas reacts vigorously with fluorine gas to produce hydrogen fluoride:

\text{H}_{2}(g)+\text{F}_{2}(g)\;\longrightarrow\;2\,\text{HF}(g)

The enthalpy change for this reaction at constant pressure is

\Delta H = -537\,\text{kJ mol}^{-1}

per mole of HF formed. A sealed reaction vessel at constant pressure and temperature is charged with

5.00\,\text{g}

of H₂ and

20.0\,\text{g}

of F₂, then ignited so that the reactants are consumed as completely as possible. (a) Write the balanced chemical equation with the smallest whole-number coefficients. (b) Identify the limiting reactant and calculate the number of moles of HF produced. (c) Determine the total enthalpy change

q

(in kilojoules) for the reaction under the stated conditions. (d) Explain qualitatively how the magnitude of

q

would differ, if at all, if the same quantities of reactants were reacted at constant volume instead of constant pressure.

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