The molar enthalpies of fusion and vaporization of water at $298 \mathrm{~K}$ are $6.01$ and $44.01 \mathrm{~kJ} \mathrm{~mol}^{-1}$, respectively. Use these values to estimate the molar enthalpy of sublimation of ice.

Calculate the work done when $50.0 \mathrm{~g}$ of tin dissolves in excess acid at $1.00$ bar and $25^{\circ} \mathrm{C}$

$$\mathrm{Sn}(s)+2 \mathrm{H}^{+}(a q) \longrightarrow \mathrm{Sn}^{2+}(a q)+\mathrm{H}_2(\mathrm{~g})$$

Assume ideal gas behavior.

Use the bond enthalpy values in Table $7.6$ to calculate the enthalpy of combustion for ethane $\left(\mathrm{C}_2 \mathrm{H}_6\right)$ :

$$\mathrm{C}_2 \mathrm{H}_6(\mathrm{~g})+\frac{7}{2} \mathrm{O}_2(g) \longrightarrow 2 \mathrm{CO}_2(g)+3 \mathrm{H}_2 \mathrm{O}(g)$$

Use the bond enthalpy data in Table $7.6$ to calculate the enthalpies of formation of the following gases:
$\mathrm{H}_2 \mathrm{NCl}$.

Use the bond enthalpy data in Table $7.6$ to calculate the enthalpies of formation of the following gases:
$\mathrm{H}_2 \mathrm{O}_2$.

Use the bond enthalpy data in Table $7.6$ to calculate the enthalpies of formation of the following gases:
$\mathrm{NH}_3$.

Use the bond enthalpy data in Table $7.6$ to calculate the enthalpies of formation of the following gases:
$\mathrm{H}_2 \mathrm{O}$ (g).

The bond enthalpy of $\mathrm{F}_2$ is $150.6 \mathrm{~kJ} \mathrm{~mol}^{-1}$. Calculate the value of $\Delta H_{\mathrm{f}}^{\circ}$ for $\mathrm{F}(g)$.

Explain why the bond enthalpy of a molecule is always defined in terms of a gas-phase reaction.

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.

From the following heats of combustion,

$$\begin{aligned} &\mathrm{CH}_3 \mathrm{OH}(l)+\frac{3}{2} \mathrm{O}_2(g) \longrightarrow \mathrm{CO}_2(g)+2 \mathrm{H}_2 \mathrm{O}(l) \\ &\mathrm{C} \text { (graphite) }+\mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}_2(\mathrm{~g}) \\ &\mathrm{H}_2(\mathrm{~g})+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{H}_2 \mathrm{O}(l) \\ & \end{aligned}$$

calculate the standard enthalpy of formation of methanol $\left(\mathrm{CH}_3 \mathrm{OH}\right)$ from its elements.

$7.33$ From the following data,

$$\begin{aligned} \mathrm{C} \text { (graphite) }+\mathrm{O}_2(g) \longrightarrow & \mathrm{CO}_2(g) \\ & \Delta H_{\mathrm{rnn}}^{\circ}=-393.5 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ \mathrm{H}_2(g)+\frac{1}{2} \mathrm{O}_2(g) \longrightarrow & \mathrm{H}_2 \mathrm{O}(l) \\ 2 \mathrm{C}_2 \mathrm{H}_6(g)+7 \mathrm{O}_2(g) \longrightarrow & \Delta H_{\mathrm{rnn}}^{\circ}=-285.8 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & 4 \mathrm{CO}_2(g)+6 \mathrm{H}_2 \mathrm{O}(l) \\ & \Delta H_{\mathrm{rnn}}^{\circ}=-3119.6 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{aligned}$$

calculate the enthalpy change for the reaction $2 \mathrm{C}$ (graphite) $+3 \mathrm{H}_2(\mathrm{~g}) \longrightarrow \mathrm{C}_2 \mathrm{H}_6(\mathrm{~g})$.

At $850^{\circ} \mathrm{C}, \mathrm{CaCO}_3$ undergoes substantial decomposition to yield $\mathrm{CaO}$ and $\mathrm{CO}_2$. Assuming that the $\Delta \mathrm{H}_{\mathrm{f}}^{\circ}$ values of the reactant and products are the same at $850^{\circ} \mathrm{C}$ as they are at $25^{\circ} \mathrm{C}$, calculate the enthalpy change (in $\mathrm{kJ}$ ) if $66.8 \mathrm{~g}$ of $\mathrm{CO}_2$ is produced in one reaction. 7.32 From these data,

$$\text { S(rhombic) }+\mathrm{O}_2(\mathrm{~g}) \underset{\Delta H_{\text {ran }}^{\circ}=-296.84 \mathrm{~kJ} \mathrm{~mol}^{-1}}{\mathrm{SO}_2(\mathrm{~g})}$$

$$\text { S(monoclinic) }+\mathrm{O}_2(\mathrm{~g}) \underset{\Delta H_{\mathrm{rn}}^{\circ}}{\longrightarrow} \mathrm{SO}_2(\mathrm{~g})$$

calculate the enthalpy change for the transformation

$$S \text { (rhombic) } \longrightarrow S \text { (monoclinic) }$$

(Monoclinic and rhombic are different allotropic forms of elemental sulfur.)

At $850^{\circ} \mathrm{C}, \mathrm{CaCO}_3$ undergoes substantial decomposition to yield $\mathrm{CaO}$ and $\mathrm{CO}_2$. Assuming that the $\Delta \mathrm{H}_{\mathrm{f}}^{\circ}$ values of the reactant and products are the same at $850^{\circ} \mathrm{C}$ as they are at $25^{\circ} \mathrm{C}$, calculate the enthalpy change (in $\mathrm{kJ}$ ) if $66.8 \mathrm{~g}$ of $\mathrm{CO}_2$ is produced in one reaction.