Problem 1
From the statements below, say whether the following processes are exothermic or endothermic. (a) The addition of caesium to water is explosive. (b) The evaporation of a few drops of diethyl ether from the palm of your hand makes your hand feel colder. (c) Burning propane gas in \(\mathrm{O}_{2} ;\) this reaction is the basis for the use of propane as a fuel. (d) Mixing aqueous solutions of \(\mathrm{NaOH}\) and \(\mathrm{HCl}\) causes the temperature of the solution to increase.
Problem 2
What are the standard states of the following elements at \(298 \mathrm{K}:\) (a) chlorine; (b) nitrogen; (c) phosphorus; (d) carbon; (e) bromine; (f) sodium; (g) fluorine?
Problem 3
The standard enthalpy of reaction for the combustion of 1 mole of \(\mathrm{Ca}\) is \(-635 \mathrm{kJ} \mathrm{mol}^{-1}\). Write a balanced equation for the process to which this value refers. Does the reaction give out or absorb heat?
Problem 4
\(100.0 \mathrm{cm}^{3}\) of aqueous hydrochloric acid, \(\mathrm{HCl}\) \(\left(2.0 \mathrm{mol} \mathrm{dm}^{-3}\right)\) were mixed with \(100.0 \mathrm{cm}^{3}\) of aqueous \(\mathrm{NaOH}\left(2.0 \mathrm{mol} \mathrm{dm}^{-3}\right)\) in a simple, constant-pressure calorimeter. A temperature rise of \(13.9 \mathrm{K}\) was recorded. Determine the value of \(\Delta H\) for the reaction in \(\mathrm{kJ}\) per mole of \(\mathrm{HCl}\). \(\begin{array}{l} \left(C_{\text {water }}=4.18 \mathrm{JK}^{-1} \mathrm{g}^{-1} ;\text {density of } \right. \\ \text { water }\left.=1.00 \mathrm{g} \mathrm{cm}^{-3}\right) \end{array}\)
Problem 5
Comment on the fact that the values of \(\Delta H\) (quoted per mole of \(\mathrm{NaOH}\) ) for the following reactions are all approximately equal: \\[\begin{array}{l}\mathrm{NaOH}(\mathrm{aq})+\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{NaCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \\\ \mathrm{NaOH}(\mathrm{aq})+\mathrm{HBr}(\mathrm{aq}) \rightarrow \mathrm{NaBr}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(1) \\\\\mathrm{NaOH}(\mathrm{aq})+\mathrm{HNO}_{3}(\mathrm{aq}) \rightarrow \mathrm{NaNO}_{3}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})\end{array}\\]
Problem 6
When \(2.3 \mathrm{g}\) of NaI dissolves in \(100.0 \mathrm{g}\) of water contained in a simple, constant-pressure calorimeter, the temperature of the solution rises by \(0.28 \mathrm{K} .\) State whether dissolving \(\mathrm{NaI}\) is an endothermic or exothermic process. Find the enthalpy change for the dissolution of 1 mole of NaI. \(\left(C_{\text {water }}=4.18 \mathrm{JK}^{-1} \mathrm{g}^{-1}\right).\)
Problem 24
(a) For crystalline \(\mathrm{KMnO}_{4}\) \(\Delta_{\mathrm{f}} H^{\mathrm{o}}(298 \mathrm{K})=-837 \mathrm{kJ} \mathrm{mol}^{-1} .\) Write an equation that describes the process to which this value refers. (b) Cyclohexane, \(\mathrm{C}_{6} \mathrm{H}_{12},\) is a liquid at \(298 \mathrm{K}\) \(\Delta_{\mathrm{c}} H^{\mathrm{o}}\left(\mathrm{C}_{6} \mathrm{H}_{12}, 1,298 \mathrm{K}\right)=-3920 \mathrm{kJ} \mathrm{mol}^{-1}\) Determine the value of \(\Delta_{\mathrm{f}} H^{\circ}\left(\mathrm{C}_{6} \mathrm{H}_{12}, 1,298 \mathrm{K}\right)\) (c) Use your answer to part (b), and the fact that \(\Delta_{\mathrm{f}} H^{\mathrm{o}}\left(\mathrm{C}_{6} \mathrm{H}_{12}, \mathrm{g}, 298 \mathrm{K}\right)=-123 \mathrm{kJ} \mathrm{mol}^{-1},\) to determine \(\Delta_{\mathrm{vap}} H^{\circ}\left(\mathrm{C}_{6} \mathrm{H}_{12}, 298 \mathrm{K}\right) .\) Why does this value differ from \(\Delta_{\mathrm{vap}} H\left(\mathrm{C}_{6} \mathrm{H}_{12}, \mathrm{bp}\right)=30 \mathrm{kJ} \mathrm{mol}^{-1} ?\)
