Concept explainers
Ethyl alcohol, C2H5OH, is the intoxicating agent in liquor. Burning 1.00 g of ethyl alcohol in an excess of oxygen at 23.28°C and constant volume releases 29.52 kJ of heat. When 7.40 g of ethyl alcohol is burned in oxygen under the same conditions in a bomb calorimeter, the temperature of the bomb and water rises from 23.28°C to 48.04°C. The bomb holds 0.750 kg of water.
(a) What is q for the combustion of the ethyl alcohol in the bomb calorimeter?
(b) What is qH2O?
(c) What is qcal?
(d) What is the heat capacity of the calorimeter?
(a)
Interpretation:
To determine q for the combustion of ethyl alcohol in bomb calorimeter.
Concept introduction:
In a bomb calorimeter, heat given off by the reaction is absorbed by the calorimeter (including metal bomb and water). Therefore,
Heat absorbed by bomb calorimeter can be calculated by using below formula:
Heat absorbed by water can be calculated by using below formula:
Answer to Problem 16QAP
q for combustion of 7.40 g of ethyl alcohol is -218.44 kJ.
Explanation of Solution
According to question:
Combustion of 1 g of ethyl alcohol releases 29.52 kJ energy.
Therefore,
q for combustion of 7.40 g of ethyl alcohol is -218.44 kJ.
Here negative sign indicates that energy is released.
(b)
Interpretation:
To determine qH2O in the given experiment.
Concept introduction:
In a bomb calorimeter, heat given off by the reaction is absorbed by the calorimeter (including metal bomb and water). Therefore,
Heat absorbed by bomb calorimeter can be calculated by using below formula:
Heat absorbed by water can be calculated by using below formula:
Answer to Problem 16QAP
qH2O is 77.62 kJ.
Explanation of Solution
According to question:
Mass of water = 0.750 kg = 750 g
Initial temperature = 23.28 °C
Final temperature = 48.04 °C
Change in temperature = 48.04 - 23.28 = 24.76 °C
Specific heat of water = 4.18 J/g°C
As we know:
Plugging values, we get:
Thus,qH2O is 77.62 kJ.
(c)
Interpretation:
To determine qcalorimeter in the given experiment.
Concept introduction:
In a bomb calorimeter, heat given off by the reaction is absorbed by the calorimeter (including metal bomb and water). Therefore,
Answer to Problem 16QAP
qcalorimeter is 140.82 kJ.
Explanation of Solution
Here we have:
qH2O = 77.62 kJ.
qreaction = -218.44 kJ. (enthalpy of reaction)
As we know:
Plugging values, we get:
Thus, qcalorimeter is 140.82 kJ.
(d)
Interpretation:
To determine the heat capacity of calorimeter in the given experiment.
Concept introduction:
Heat absorbed by bomb calorimeter can be calculated by using below formula:
Answer to Problem 16QAP
Heat capacity of bomb calorimeter is 5.68 kJ/°C
Explanation of Solution
Here we have:
qcalorimeter = 140.82 kJ.
Change in temperature = 24.76°C
As we know:
Plugging values, we get:
Thus, heat capacity of bomb calorimeter is 5.68 kJ/°C
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Chapter 8 Solutions
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