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Gaseous State: Dalton's Law Of Partial Pressure

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Gaseous State: Dalton's Law Of Partial Pressure - Lesson Summary

In 1807, John Dalton studied the pressure exerted by a mixture of non-reacting gases enclosed in a vessel.

According to Dalton's law of partial pressures, "The total pressure exerted by a mixture of two or more non-reacting gases enclosed in a vessel at a given temperature is equal to the sum of the partial pressures exerted by individual gases if they were enclosed separately in that vessel at the same temperature.

Mathematically it can be written as:

Ptotal = p1 + p2 + p3

Ptotal = total pressure exerted by the mixture of gases.

p1, p2, p3 are partial pressures of individual gases.

On applying the ideal gas equation,

P1 = n1RT/V      P2 = n2RT/V        P3 = n3RT/V

          PTotal = p1 + p2 + p3

         PTotal  = n1RT/V + n2RT/V + n3RT/V

         PTotal  = (n1 + n2 + n3)RT/V

         P1/PTotal =  n1/(n1 + n2 + n3) RT / V . V / RT

         P1/PTotal =  n1/(n1 + n2 + n3)

         P1/PTotal =  n1/n

                 n = n1 + n2 + n3

               n1/n = x1

        P1/PTotal = x1

       P1 = x1 PTotal

          P2 = x2 PTotal
          P3 = x3 PTotal

 Pi = xi PTotal

Pi = partial pressure of ith gas                            xi = mole fraction of ith gas

Dalton's law of partial pressures is useful in calculating the pressure of the gas collected over water by the downward displacement in the laboratory.


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