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Chapter 5: Q42 E (page 227)
Calculate 鈭咹 for the reaction described by the equation. (Hint: use the value for the approximate amount of heat absorbed by the reaction that you calculated in a previous exercise.)
Ba(OH)2. 8H2O(s) + 2NH4SCN(aq) 鈫� Ba(SCN)2(aq) + 2NH3(aq) + 10H2O(l)
The enthalpy of the reaction is 140 kJ/mol.
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A sample of 0.562 g of carbon is burned in oxygen in a bomb calorimeter, producing carbon dioxide. Assume both the reactants and products are under standard state conditions, and that the heat released is directly proportional to the enthalpy of combustion of graphite. The temperature of the calorimeter increases from 26.74 掳C to 27.93 掳C. What is the heat capacity of the calorimeter and its contents?
Aluminum chloride can be formed from its elements:
(i)\({\bf{2Al(s) + 3C}}{{\bf{l}}_{\bf{2}}}{\bf{(g)}} \to {\bf{2AlC}}{{\bf{l}}_{\bf{3}}}{\bf{(s) \Delta H^\circ = ?}}\)
Use the reactions here to determine the 螖H掳 for reaction(i):
\(\begin{array}{*{20}{l}}{\left( {{\bf{ii}}} \right){\rm{ }}{\bf{HCl(g)}} \to {\bf{HCl(aq) \Delta H^\circ (ii) = - 74}}{\bf{.8 kJ}}}\\{\left( {{\bf{iii}}} \right){\rm{ }}{{\bf{H}}_{\bf{2}}}{\bf{(g) + C}}{{\bf{l}}_{\bf{2}}}{\bf{(g)}} \to {\bf{2HCl(g) \Delta H^\circ (iii) = - 185 kJ}}}\\{\left( {{\bf{iv}}} \right){\rm{ }}{\bf{AlC}}{{\bf{l}}_{\bf{3}}}{\bf{(aq)}} \to {\bf{AlC}}{{\bf{l}}_{\bf{3}}}{\bf{(s) \Delta H^\circ (iv) = + 323 kJ}}}\\{\left( {\bf{v}} \right){\rm{ }}{\bf{2Al(s) + 6HCl(aq)}} \to {\bf{2AlC}}{{\bf{l}}_{\bf{3}}}{\bf{(aq) + 3}}{{\bf{H}}_{\bf{2}}}{\bf{(g) \Delta H^\circ (v) = - 1049 kJ}}}\end{array}\)
Ethanol, \({{\bf{C}}_{\bf{2}}}{{\bf{H}}_{\bf{5}}}{\bf{OH}}\), is used as a fuel for motor vehicles, particularly in Brazil.
(a) Write the balanced equation for the combustion of ethanol to CO2(g) and H2O(g), and, using the data in Appendix G, calculate the enthalpy of combustion of 1 mole of ethanol.
(b) The density of ethanol is 0.7893 g/ml. Calculate the enthalpy of combustion of exactly 1 L of ethanol.
(c) Assuming that an automobile鈥檚 mileage is directly proportional to the heat of combustion of the fuel, calculate how much farther an automobile could be expected to travel on 1 L of gasoline than on 1 L of ethanol. Assume that gasoline has the heat of combustion and the density of n鈥搊ctane, \({{\bf{C}}_{\bf{8}}}{{\bf{H}}_{{\bf{18}}}}\) (螖Hf=
- 208.4 kJ/mol; density = 0.7025 g/mL).
Calculate \[{\bf{\Delta H}}_{{\bf{298 }}}^{\bf{^\circ }}\] for the process \[{\bf{C}}{{\bf{o}}_{\bf{3}}}{{\bf{O}}_{\bf{4}}}\left( {\bf{s}} \right) \to {\bf{3Co}}\left( {\bf{s}} \right){\bf{ + 2}}{{\bf{O}}_{\bf{2}}}\left( {\bf{g}} \right)\]
from the following information:
\[\begin{array}{c}{\bf{Co(s) + }}\frac{{\bf{1}}}{{\bf{2}}}{{\bf{O}}_{\bf{2}}}{\bf{(g)}} \to {\bf{CoO(s) \Delta H}}_{{\bf{298}}}^{\bf{^\circ }}{\bf{ = - 237}}{\bf{.9kJ}}\\{\bf{3CoO(s) + }}\frac{{\bf{1}}}{{\bf{2}}}{{\bf{O}}_{\bf{2}}}{\bf{(g)}} \to {\bf{C}}{{\bf{o}}_{\bf{3}}}{{\bf{O}}_{\bf{4}}}{\bf{(s) \Delta H}}_{{\bf{298}}}^{\bf{^\circ }}{\bf{ = - 177}}{\bf{.5kJ}}\end{array}\]
How many moles of isooctane must be burned to produce 100 kJ of heat under standard state conditions?
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