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Chapter 5: QCYL (page 254)
When 1.34 g Zn(s) reacts with 60.0 mL of 0.750 M HCl(aq), 3.14 kJ of heat are produced. Determine the enthalpy change per mole of zinc reacting for the reaction:
\({\bf{Zn(s) + 2HCl(aq)}} \to {\bf{ZnC}}{{\bf{l}}_{\bf{2}}}{\bf{(aq) + }}{{\bf{H}}_{\bf{2}}}{\bf{(g)}}\)
Enthalpy change = -153.86 kJ.
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When 1.0g of fructose, C6H12O6(s), a sugar commonly found in fruits, is burned in oxygen in a bomb calorimeter, the temperature of the calorimeter increases by 1.58˚C. If the heat capacity of the contents is 9.90kJ/˚C, what is q for this combustion?
The temperature of the cooling water as it leaves the hot engine of an automobile is 240°F. After it passes through the radiator it has a temperature of 175°F. Calculate the amount of heat transferred from the engine to the surroundings by one gallon of water with a specific heat of 4.184 J/g°C.
In the early days of automobiles, illumination at night was provided by burning acetylene, C2H2. Though no longer used as auto headlamps, acetylene is still used as a source of light by some cave explorers. The acetylene is (was) prepared in the lamp by the reaction of water with calcium carbide, CaC2:
\({\bf{Ca}}{{\bf{C}}_{\bf{2}}}\left( {\bf{s}} \right){\bf{ + 2}}{{\bf{H}}_{\bf{2}}}{\bf{O}}\left( {\bf{l}} \right) \to {\bf{Ca}}{\left( {{\bf{OH}}} \right)_{\bf{2}}}\left( {\bf{s}} \right){\bf{ + }}{{\bf{C}}_{\bf{2}}}{{\bf{H}}_{\bf{2}}}\left( {\bf{g}} \right)\)
Calculate the standard enthalpy of the reaction. The \({\bf{\Delta H}}_{\bf{f}}^{\bf{o}}\)of CaC2is -15.14 kcal/mol.
Would the amount of heat measured for the reaction in example 5.5be greater, lesser, or remain the same if we used a calorimeter that was a poorer insulator than a coffee cup calorimeter? Explain your answer.
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’s 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–octane, \({{\bf{C}}_{\bf{8}}}{{\bf{H}}_{{\bf{18}}}}\) (ΔHf=
- 208.4 kJ/mol; density = 0.7025 g/mL).
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