2.0 L of gas A at 1.0 atm and 1.0 L of gas B at 1.0 atm are combined in a 3.0 L flask. The flask is sealed and over time they react completely to give gas C according to the following chemical equation: 2A(g) + B(g) →C(g) Assuming the temperature stays constant, what will be the pressure after the reaction goes to completion?

This can be calculated using Dalton's law of partial pressure which states that if two or more gases are mixed together, the total pressure exerted by the mixture of the gases is eqaul to the sum of the pressure which individual gas woud exert if it occupied the volume of of the mixture alone.

Therefore P (total) = P (gas A) + P (gas B)

Since pressure of gas A = 1.0 atm

pressure of gas B = 1.0 atm

gas constant R = 0.08206 atm L mol-1 K-1

standard temperature = 273K

Note that atm is a unit for pressure

Number of mole of gas A, n=PV/RT

= 1 x 2 / 0.08206 x 273

= 0.088306 mole

Number of mole of gas B

= 1 x 1 / 0.08206 x 273

= 0.044644 mole

Total pressure can be gotten using P(total) = (n(total)RT)/V(total)

= [(0.044644 + 0.088306) x 0.08206 x 273] / 3

= 0.993 atm