Chapter 6: Problem 40
How are the standard enthalpies of an element and a compound determined?
Chapter 6: Problem 40
How are the standard enthalpies of an element and a compound determined?
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Get started for freeDecomposition reactions are usually endothermic, whereas combination reactions are usually exothermic. Give a qualitative explanation for these trends.
Calculate the standard enthalpy of formation for diamond, given that $$\begin{array}{l} \text { C(graphite) }+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g) \\ \qquad \begin{aligned} \Delta H^{\circ} &=-393.5 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{C}(\text { diamond })+\mathrm{O}_{2}(g) \longrightarrow & \mathrm{CO}_{2}(g) \\ \Delta H^{\circ} &=-395.4 \mathrm{~kJ} / \mathrm{mol} \end{aligned} \end{array}$$
Determine the standard enthalpy of formation of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) from its standard enthalpy of combustion \((-1367.4 \mathrm{~kJ} / \mathrm{mol})\)
A 3.53-g sample of ammonium nitrate \(\left(\mathrm{NH}_{4} \mathrm{NO}_{3}\right)\) was added to \(80.0 \mathrm{~mL}\) of water in a constantpressure calorimeter of negligible heat capacity. As a result, the temperature of the water decreased from \(21.6^{\circ} \mathrm{C}\) to \(18.1^{\circ} \mathrm{C}\). Calculate the heat of solution \(\left(\Delta H_{\mathrm{soln}}\right)\) of ammonium nitrate.
A 4.117 -g impure sample of glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)\) was burned in a constant-volume calorimeter having a heat capacity of \(19.65 \mathrm{~kJ} /{ }^{\circ} \mathrm{C}\). If the rise in temperature is \(3.134^{\circ} \mathrm{C},\) calculate the percent by mass of the glucose in the sample. Assume that the impurities are unaffected by the combustion process. See Appendix 2 for thermodynamic data.
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