“ Gasohol” is a mixture of gasoline and ethyl alcohol used as automobile fuel. T
ID: 904447 • Letter: #
Question
“Gasohol” is a mixture of gasoline and ethyl alcohol used as automobile fuel. The alcohol produces energy in a combustion reaction with O2.
C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(l)
If 0.115 g of alcohol evolves 3.42 kJ when burned at constant pressure, what is the molar enthalpy of combustion for ethyl alcohol?
Chemical cold packs contain two pouches, one containing solid ammonium nitrate and the other containing water (often dyed for no real reason). When the contents of the pouches mix, the ammonium nitrate dissolves in the water, NH4NO3(s) NH4+(aq) + NO3-(aq)
The dissolving process is endothermic. The reaction absorbs approximately 326 J/g of ammonium nitrate. To lower the temperature of 220. g of water by 20.0°C, how many grams of ammonium nitrate would you need to dissolve?
When Voyager 2 encountered the planet Saturn in 1981, the planet was approximately 1 billion miles (1 X 109 mi) from the Earth. How long did it take for the television picture signal to reach the Earth from Saturn? (1 mile = 1.61 km)
If energy is absorbed by a hydrogen atom in its ground state, the atom is excited to a higher energy state. For example, the excitation of an electron from the orbital with n=1 to an orbital with n=4 requires radiation with a wavelength of 97.2 nm. Which of the following transitions would require radiation of longer wavelength than this?
a. n=2 to n=4 b. n=1 to n=3
c. n=1 to n=3 d. n=3 to n=5
You add 100.0g of water at 55.0C to 100.0g of ice at 0.00C. Some of the ice melts and cools the water to 0.00C. When thermal equilibrium is established at 0.00C, what mass of ice has melted?
Delta H of fusion for water is 333 J/g.
Explanation / Answer
First calculate the moles of alcohol as follows:
0.115 g of alcohol / molar mass = 0.115 g /46.06844 g/mol = 2.50*10^-3 mol
Given that,
2.50*10^-3 mol of alcohol evolves = 3.42 kJ
1.0 mol of alcohol will evolve = 3.42 kJ/ 2.50*10^-3 mol = 1368 KJ
Hence the molar enthalpy of combustion for ethyl alcohol is 1368 KJ.
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