A rigid stainless steel chamber contains 260 Torr of methane, CH4, and excess oxygen, O2, at 170.0 °C. A spark is ignited inside the chamber, completely combusting the methane. What is the change in total pressure within the chamber following the reaction? Assume a constant temperature throughout the process.
ΔP = _________ Torr
CH4 + 2O2 ---> CO2 + 2H2O
According the above reaction
260 torr of CH4 pressure means at least 520 torr of O2
pressure. Since it is excess, let us call the O2 pressure 520 +
x.
Let us consider the CH4 to CO2 molar ratio of 1 to 1. Since this
happens at constant volume and constant temperature, the pressures
are directly related to the moles used and produced. Thus, we
conclude 260 torr of CO2 pressure is produced.
Since we are at 170 C, the water produced is gaseous. Let us
consider the CH4 to H2O molar ratio of 1 to 2. This informs us that
520 torr of water vapor pressure is created.
Since O2 is in excess, we know that x remains after 520 torr of O2
is used up. I know 520 torr of O2 is used because of the CH4 to O2
molar ratio in the balanced equation.
Conclusion: no pressure change in the chamber at reaction's
end.
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