Dalton's law of partial pressure states that **"the total pressure exerted by a mixture of gases is the sum of the partial pressure of the individual gases present."** A partial pressure is the pressure that a gas in a mixture of gases would exert if it were present alone under the same conditions.

**Dalton's Law Formula **is mathematically expressed as

Where

P_{total} = the total pressure of a gaseous mixture and

P_{1}, P_{2}, P_{3} and so on are the partial pressures of the individual gaseous components of the mixture.

P

P

Dalton's law describes the effect of gas composition on the pressures that the gas exerts on its surroundings.

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Solved problems based on Dalton's law are given below. ### Solved Examples

**Question 1: **Three gases, Ar, N_{2 }and H_{2} are mixed in a 500L container. Ar has a pressure of 255 torr, N_{2} has a pressure of 228torr and H_{2} has pressure of 752torr. What is the total pressure in the container?

** Solution: **

According to Dalton's law the total pressure is the sum of the partial pressures of each gas. Add the three partial pressures together.

P_{Ar} = 255torr, PN_{2 }= 228torr, PH_{2} = 752torr

P_{total} = P_{Ar }+ PN_{2} + PH_{2} = 255torr + 228torr + 752torr

P_{total} = 1235torr

**Question 2: **Calculate the partial pressure of H_{2} at 20^{o}C when the vapor pressure of water is 17.5torr. The total pressure of the gases is 750torr.

** Solution: **

Given

P_{total} = 750torr

P_{H2O} = 17.5torr

P_{H2} = ?

P_{total} = P_{H2O} + P_{H2}

750torr = 17.5torr + P_{H2}

P_{H2} = 732torr

According to Dalton's law the total pressure is the sum of the partial pressures of each gas. Add the three partial pressures together.

P

P

P

Given

P

P

P

P

750torr = 17.5torr + P

P