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Combustion Reactions- Thermochemistry

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1. A constant-volume tank consists of a mixture of 120 grams of methane (CH4) gas and 600 grams of O2 at 25 degrees C and 200 kPa. The contents of the tank are now ignited, and the methane gas burns completely. If the final temperature is 1200K, determine (a) the final pressure in the tank, (b) the dry analysis of the product stream and (c) the heat transfer during the process. Please note that no nitrogen participates in this reaction.

2. Determine the highest possible temperature that can be obtained when liquid octane (C8H18) at 25 degrees C is burned steadily with air at 25 degrees C.

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This solution is provided in 635 words in an attached .doc file. It provides comprehensive step-by-step instructions for solving the problem, including finding atomic mass balance and engaging in energetic analysis.

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Solution 1:


Nx = number of kmols of component (x)
rx = the molar (volumetric) percentage of component "x" in a mixture
Q = molar heat exchange (kJ/kmol)
 = universal constant of gases,  = 8.314 kJ/kmol.K
Cp = molar specific heat at constant pressure (kJ/kmol.K)
CV = molar specific heat at constant volume (kJ/kmol.K)
 = oxygen excess coefficient
 = volumetric ratio nitrogen/oxygen of air composition

a) The final pressure in the tank
The stoichiometric oxidation reaction of methane is:
( 1)
The atomic mass balance leads to:
( 2)
The stoichiometric oxygen/methane mass ratio is 64:16 = 4:1.
The actual oxygen/methane ratio is 600g/120g = 5:1, that means there is an excess of oxygen which will not participate to the reaction:
( 3)
In order to find (), we need to solve the equation:
( 4)
If we want to find the final pressure in the tank, we need to apply the ideal gases law for reactants and for reaction products, in the molar form:
( 5)
Since V1 = V2 (isochoric process), we can write:

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