Problem 69
Methanol, ethanol, and \(n\) -propanol are three common alcohols. When \(1.00 \mathrm{~g}\) of each of these alcohols is burned in air, heat is liberated as follows: (a) methanol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right),-22.6 \mathrm{~kJ} ;(\mathrm{b})\) ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right),-29.7 \mathrm{~kJ} ;\) (c) \(n\) -propanol \(\left(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}\right),-33.4 \mathrm{~kJ} .\) Calculate the heats of combustion of these alcohols in \(\mathrm{kJ} / \mathrm{mol}\).
Problem 70
The standard enthalpy change for the following reaction is \(436.4 \mathrm{~kJ} / \mathrm{mol}\) : $$\mathrm{H}_{2}(g) \longrightarrow \mathrm{H}(g)+\mathrm{H}(g)$$ Calculate the standard enthalpy of formation of atomic hydrogen (H).
Problem 73
Consider the reaction \(\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g) \quad \Delta H=-92.6 \mathrm{~kJ} / \mathrm{mol}\) When \(2 \mathrm{~mol}\) of \(\mathrm{N}_{2}\) react with \(6 \mathrm{~mol}\) of \(\mathrm{H}_{2}\) to form \(4 \mathrm{~mol}\) of \(\mathrm{NH}_{3}\) at 1 atm and a certain temperature, there is a decrease in volume equal to \(98 \mathrm{~L}\). Calculate \(\Delta U\) for this reaction. (The conversion factor is \(1 \mathrm{~L} \cdot \mathrm{atm}=101.3 \mathrm{~J} .\)
Problem 74
Calculate the heat released when \(2.00 \mathrm{~L}\) of \(\mathrm{Cl}_{2}(g)\) with a density of \(1.88 \mathrm{~g} / \mathrm{L}\) reacts with an excess of sodium metal at \(25^{\circ} \mathrm{C}\) and 1 atm to form sodium chloride.
Problem 76
Determine the amount of heat (in kJ) given off when \(1.26 \times 10^{4} \mathrm{~g}\) of ammonia is produced according to the equation \(\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g) \quad \Delta H_{\mathrm{rxn}}^{\circ}=-92.6 \mathrm{~kJ} / \mathrm{mol}\) Assume that the reaction takes place under standardstate conditions at \(25^{\circ} \mathrm{C}\).
Problem 77
Predict the value of \(\Delta H_{\mathrm{f}}^{\circ}\) (greater than, less than, or equal to zero) for these elements at \(25^{\circ} \mathrm{C}:\) (a) \(\mathrm{Br}_{2}(g)\), \(\mathrm{Br}_{2}(l) ;(\mathrm{b}) \mathrm{I}_{2}(g), \mathrm{I}_{2}(s)\).
Problem 79
Suggest ways (with appropriate equations) that would allow you to measure the \(\Delta H_{\mathrm{f}}^{\circ}\) values of \(\mathrm{Ag}_{2} \mathrm{O}(s)\) and \(\mathrm{CaCl}_{2}(s)\) from their elements. No calculations are necessary.
Problem 81
The convention of arbitrarily assigning a zero enthalpy value for the most stable form of each element in the standard state at \(25^{\circ} \mathrm{C}\) is a convenient way of dealing with enthalpies of reactions. Explain why this convention cannot be applied to nuclear reactions.
Problem 82
Consider the following two reactions: $$ \begin{array}{ll} \mathrm{A} \longrightarrow 2 \mathrm{~B} & \Delta H_{\mathrm{rxn}}^{\circ}=H_{1} \\\ \mathrm{~A} \longrightarrow \mathrm{C} & \Delta H_{\mathrm{rxn}}^{\circ}=H_{2} \end{array} $$ Determine the enthalpy change for the process $$ 2 \mathrm{~B} \longrightarrow \mathrm{C} $$
Problem 83
The standard enthalpy change \(\Delta H^{\circ}\) for the thermal decomposition of silver nitrate according to the following equation is \(+78.67 \mathrm{~kJ}\) : \(\mathrm{AgNO}_{3}(s) \longrightarrow \mathrm{AgNO}_{2}(s)+\frac{1}{2} \mathrm{O}_{2}(g)\) The standard enthalpy of formation of \(\mathrm{AgNO}_{3}(s)\) is \(-123.02 \mathrm{~kJ} / \mathrm{mol} .\) Calculate the standard enthalpy of formation of \(\mathrm{AgNO}_{2}(s)\).
