Unit 5 Thermodynamics
5.5 Exercises
OpenStax
Section 5.5 Exercises
- Calculate [latex]\Delta S^{\circ}_{298}[/latex] for the following changes.
(a) [latex]\text{SnCl}_4(l)\;{\longrightarrow}\;\text{SnCl}_4(g)[/latex]
(b) [latex]\text{CS}_2(g)\;{\longrightarrow}\;\text{CS}_2(l)[/latex]
(c) [latex]\text{Cu}(s)\;{\longrightarrow}\;\text{Cu}(g)[/latex]
(d) [latex]\text{H}_2\text{O}(l)\;{\longrightarrow}\;\text{H}_2\text{O}(g)[/latex]
(e) [latex]2\text{H}_2(g)\;+\;\text{O}_2(g)\;{\longrightarrow}\;2\text{H}_2\text{O}(l)[/latex]
(f) [latex]2\text{HCl}(g)\;+\;\text{Pb}(s)\;{\longrightarrow}\;\text{PbCl}_2(s)\;+\;\text{H}_2(g)[/latex]
(g) [latex]\text{Zn}(s)\;+\;\text{CuSO}_4(s)\;{\longrightarrow}\;\text{Cu}(s)\;+\;\text{ZnSO}_4(s)[/latex]
- Determine the entropy change for the combustion of gaseous propane, C3H8, under standard state conditions to give gaseous carbon dioxide and water vapour.
- Using the relevant [latex]S_{298}^{\circ}[/latex] values (Source: OpenStax Chemistry 2e) listed, calculate [latex]\Delta S_{298}^{\circ}[/latex] for:
[latex]\text{N}_2(g)\;+\;\frac{5}{2}\text{O}_2(g)\;{\longrightarrow}\;\text{N}_2\text{O}_5(g)[/latex]
- By calculating ΔSuniv at each temperature, determine if the melting of 1 mole of NaCl(s) is spontaneous at 500 °C and at 700 °C. Hint: ΔH = qsystem.
[latex]S_{\text{NaCl}(s)}^{\circ} = 72.11\;\frac{\text{J}}{\text{mol}{\cdot}\text{K}}\;\;\;\;\;\;\;S_{\text{NaCl}(l)}^{\circ} = 95.06\;\frac{\text{J}}{\text{mol}{\cdot}\text{K}}\;\;\;\;\;\;\;{\Delta}H_{\text{fusion}}^{\circ} = 27.95\;\text{kJ}/\text{mol}[/latex]What assumptions are made about the thermodynamic information (entropy and enthalpy values) used to solve this problem?
- Use the standard entropy data (Source: OpenStax Chemistry 2e) to determine the change in entropy for each of the reactions. All are run under standard state conditions and 25 °C.
(a) [latex]\text{C}(s\text{, graphite})\;+\;\text{O}_2(g)\;{\longrightarrow}\;\text{CO}_2(g)[/latex]
(b) [latex]\text{O}_2(g)\;+\;\text{N}_2(g)\;{\longrightarrow}\;2\text{NO}(g)[/latex]
(c) [latex]2\text{Cu}(s)\;+\;\text{S}(g)\;{\longrightarrow}\;\text{Cu}_2\text{S}(s)[/latex]
(d) [latex]\text{CaO}(s)\;+\;\text{H}_2\text{O}(l)\;{\longrightarrow}\;\text{Ca(OH)}_2(s)[/latex]
(e) [latex]\text{Fe}_2\text{O}_3(s)\;+\;3\text{CO}(g)\;{\longrightarrow}\;2\text{Fe}(s)\;+\;3\text{CO}_2(g)[/latex]
(f) [latex]\text{CaSO}_4\;{\cdot}\;2\text{H}_2\text{O}(s)\;{\longrightarrow}\;\text{CaSO}_4(s)\;+\;2\text{H}_2\text{O}(g)[/latex]
Solutions
- (a) 107 J/K; (b) −86.7 J/K; (c) 133.2 J/K; (d) 118.8 J/K; (e) −326.6 J/K; (f) −171.9 J/K; (g) −7.2 J/K
- 100.3 J/K
- −348.9 J/K
- As ΔSuniv < 0 at each of these temperatures, melting is not spontaneous at either of them, ΔSuniverse = −13.2 J/K at 500 °C, −5.2 J/K at 700 °C. The given values for entropy and enthalpy are for NaCl at 298 K. It is assumed that these do not change significantly at the higher temperatures used in the problem.
- (a) 2.86 J/K; (b) 24.8 J/K; (c) −113.2 J/K; (d) −24.7 J/K; (e) 15.5 J/K; (f) 290.0 J/K
