A 9.15 g sample of 3-ethylhexane (formula C 8 H 18 ), is mixed with 373.03 atm o

Question

A 9.15 g sample of 3-ethylhexane (formula C8H18), is mixed with 373.03 atm of O2 in a 1.15×10-1 L combustion chamber at 237.33 °C. The combustion reaction to CO2 and H2O is initiated and the vessel is cooled back to 237.33 °C. Report all answers to two decimal places in standard notation (i.e. 1.23 atm).


1. What is PCO2 (in atm) in the combustion chamber assuming the reaction goes to completion? Assume all water is water vapour and that the volume of the system does not change.

2. What is PO2 (in atm) in the combustion chamber after the reaction goes to completion?

Explanation / Answer

2C8H18 + 25O2 ---> 16CO2 + 18H2O(g)

no of mol of c8h18 = 9.15/114 = 0.08 mol

no of mol of o2 = PV/RT = (373.03*0.115)/(0.0821*(273.15+237.33))

                = 1.02 atm

limiting reactant = C8H18

no of mol of CO2 produced = 0.08*16/2 = 0.64 mol

pressure of co2 = 0.64*0.0821*(273.15+237.33)/0.115

                = 233.24 atm

no of mol of H2O produced = 0.08*18/2 = 0.72 mol

pressure of H2O = 0.72*0.0821*(273.15+237.33)/0.115

                = 262.4 atm

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