Chapter 5: Problem 95
What is meant by fuel value?
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Chapter 5: Problem 95
What is meant by fuel value?
These are the key concepts you need to understand to accurately answer the question.
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When measuring the enthalpy of combustion of a very small amount of material, would you prefer to use a calorimeter having a heat capacity that is small or large? Explain your reasoning.
Acetylene, \(\mathrm{C}_{2} \mathrm{H}_{2}\left(\Delta H_{\mathrm{f}}^{\circ}=226.7 \mathrm{kJ} / \mathrm{mol}\right),\) and benzene, \(\mathrm{C}_{6} \mathrm{H}_{6}\left(\Delta H_{\mathrm{f}}^{\circ}=49.0 \mathrm{kJ} / \mathrm{mol}\right),\) are sometimes referred to as endothermic compounds. a. Why are \(\mathrm{C}_{2} \mathrm{H}_{2}\) and \(\mathrm{C}_{6} \mathrm{H}_{6}\) called endothermic compounds? b. Calculate the standard molar enthalpy of combustion of acetylene and benzene.
The destruction of the ozone layer by chlorofluorocarbons (CFCs) can be described by the following reactions: $$\begin{aligned} \mathrm{ClO}(g)+\mathrm{O}_{3}(g) \rightarrow \mathrm{Cl}(g)+2 \mathrm{O}_{2}(g) & & \Delta H_{\mathrm{rxn}}=-29.90 \mathrm{kJ} \\ 2 \mathrm{O}_{3}(g) \rightarrow 3 \mathrm{O}_{2}(g) & & \Delta H_{\mathrm{rxn}}=24.18 \mathrm{kJ} \end{aligned}$$ Determine the value of the heat of reaction for the following: $$\mathrm{Cl}(g)+\mathrm{O}_{3}(g) \rightarrow \mathrm{ClO}(g)+\mathrm{O}_{2}(g) \quad \Delta H_{\mathrm{rxn}}=?$$
Baking soda decomposes on heating as follows, creating the holes in baked bread: $$2 \mathrm{NaHCO}_{3}(s) \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}(s)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(\ell)$$ Calculate the standard enthalpy of formation of \(\mathrm{NaHCO}_{3}(s)\) from the following information: $$\begin{aligned} \Delta H_{\mathrm{rxn}}^{\circ} &=-129.3 \mathrm{kJ} & \Delta H_{\mathrm{f}}\left[\mathrm{Na}_{2} \mathrm{CO}_{3}(s)\right] &=-1131 \mathrm{kJ} / \mathrm{mol} \\ \Delta H_{\mathrm{f}}\left[\mathrm{CO}_{2}(g)\right] &=-394 \mathrm{kJ} / \mathrm{mol} & \Delta H_{5}^{\mathrm{C}}\left[\mathrm{H}_{2} \mathrm{O}(\ell)\right] &=-286 \mathrm{kJ} / \mathrm{mol} \end{aligned}$$
Explain why the heats of formation of elements in their standard states are zero.
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