# 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?

Dec 2, 2015

$\implies {P}_{C} = 44.3 k P a$

#### 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 $1 a t m = 101.325 k P a$

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:

${P}_{\text{total}} = {P}_{A} + {P}_{B} + {P}_{C}$

$\implies {P}_{C} = {P}_{\text{total}} - {P}_{A} - {P}_{B}$

$\implies {P}_{C} = 101.325 k P a - 38.0 k P a - 19.0 k P a = 44.3 k P a$

Dec 2, 2015

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