An open vessel at 27*C is heated until 75% of the air in it has been expelled. Assuming the volume of the vessel remains constant, the temperature to which the vessel has been heated is ___?

Let the number of moles of air pesent in the vessel = n

75% means ¾ th of the original moles of gas has been expelled.

Therefore, the remaining number of moles of air in the vessel = (n – ¾ n)

   =  ¼ n

At constant pressure and volume,

n₁T₁= n₂T₂

n x 300 = ¼ n x T₂

T₂ = 1200 K = 927 degree Celcius

Hence, the temperature to which the vessel has been heated is 927 degree Celcius.