# Dalton’s Law of Partial Pressure | Gases | Physics Grade XI

### Gases # Dalton’s Law of Partial Pressure | Gases

Dalton’s Law of Partial pressure
It states that "the total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of the individual gas when there is no chemical interaction between them". Consider two bulbs A and B separated by a tap key T. Let the bulb A has volume V1 and gas at pressure P1. At bulb B let the volume be V2 and the pressure is P2. When the tap is opened, the final volume occupied by the gas is (V1 + V2). Experimentally, it is found that total pressure exerted by the mixture of gases is
P = {P1V1/(V1+V2) + P2V2/(V1+V2)} …… (i)

If P1' and P2' are the pressure exerted by first and second gas when they are mixed, then the total pressure of the mixture can be written as
P = P1P2' …………… (ii)

For the first gas,
P1V1 = P1' (V1 + V2)
or P1' = P1V1/ (V1 + V2)

For second gas,
P2V2 = P2' (V1 + V2)
or, P2' = P2V2/ (V1 + V2)

Putting values of P1' and P2' in (ii), we get
P = {P1V1/(V1+V2) + P2V2/(V1+V2)} …… (iii)

Since from equation (i) and (ii), the total pressure exerted by the mixture of gases is same, which is the sum of partial pressure exerted by a mixture of gases. Hence it proves Dalton’s law of partial pressure.

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