Question

Gas samples A, B, C are contained at STP. Partial pressure of sample A is 38.0 kPa and sample B is 19.0 kPa. What is the partial pressure of sample C?

Answer 1

`=>P_C=44.3kPa`

Explanation:

If the mixture of gases A, B and C is contained at STP, this means that the total pressure is 1 atm.

Note that `1atm=101.325kPa`

According to Dalton's law, the total pressure of a mixture is equal to the sum of the partial pressures of the gases in the mixture:

`P_("total")=P_A+P_B+P_C`

`=>P_C=P_("total")-P_A-P_B`

`=>P_C=101.325kPa-38.0kPa-19.0kPa=44.3kPa`

Answer 2

Pressures are additive. The pressure exerted by C is approx. 44 kPa.

Explanation:

Dalton's law of partial pressures states that in a gaseous mixture the partial pressure exerted by each component is the same pressure it would exert if it ALONE occupied the container; the total pressure is the sum of the partial pressures. We know that the total pressure is atmospheric, 101.3 kPa. Since the partial pressures, `P_A`, and `P_B` are known, `P_C` is simply the difference between these pressures and the total pressure:

`P_C = 101.3 - P_A - P_B = ?? kPa`