A constant-volume tank contains a mixture of 1 mol of H2 and 0.5 mol of O2 at 25°C and 1 atm. The contents of the tank are ignited, and the final temperature and pressure in the tank are 2800 K and 5 atm, respectively. If the combustion gases consist of H2O, H2, and O2, determine (a) the equilibrium composition of the product gases and (b) the amount of heat transfer from the combustion chamber. Is it realistic to assume that no OH will be present in the equilibrium mixture?
a)
The equilibrium composition of mixture of
Answer to Problem 93RP
The equilibrium composition of mixture of
Explanation of Solution
Write the stoichiometric reaction for dissociation of water.
From Equation (I), infer that the stoichiometric coefficient for oxygen
Write the actual reaction for the combustion process.
From Equation (II), infer that the equilibrium composition contains x amount of
Write the formula for total number of moles
Substitute x for
Write the equilibrium constant
Here, pressure is P.
Conclusion:
Refer the table A-28, “Natural logarithm of equilibrium constants’, obtain the value of
Substitute
Substitute 0.944 for x in Equation (II).
Thus, the equilibrium composition of mixture of
b)
The amount of heat released per kg of hydrogen.
Answer to Problem 93RP
The amount of heat released per kg of hydrogen is
Explanation of Solution
Write the energy balance equation for the combustion process.
Here, heat released during combustion is
Conclusion:
Refer the table A-26, “Enthalpy of formation table”, obtain the enthalpy of
Refer the table A-18, “Ideal gas properties of hydrogen gas”, obtain the following properties of hydrogen gas at different temperature.
Enthalpy of hydrogen gas at 2800 K,
Enthalpy of hydrogen gas at 298 K,
Refer the table A-19, “Ideal gas properties of oxygen gas”, obtain the following properties of oxygen gas at different temperature.
Enthalpy of oxygen gas at 2800 K,
Enthalpy of oxygen gas at 298 K,
Refer the table A-19, “Ideal gas properties of water vapor”, obtain the following properties of water vapor at different temperature
Enthalpy of water vapor at 2800 K,
Enthalpy of water vapor at 298 K,
Substitute
Thus, the amount of heat released per kg of hydrogen is
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Chapter 16 Solutions
Thermodynamics: An Engineering Approach
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