Q.

The temperature of a gas is – 78°C and the average translational kinetic energy of its molecules is K. The temperature at which the average translational kinetic energy of the molecules of the same gas becomes 2K is              [2024]

1 – 39°C  
2 117°C  
3 127°C  
4 – 78°C  

Ans.

(2)   

       Average translational kinetic energy

        E=32KBT

       At – 78°C = 273 – 78 = 195 K

       K=32KB×(195K)                                            ...(i)

      Now when kinetic energy becomes 2K, the temperature is T K.

        2K=32KB×(T K)                                    ...(ii)

      From equations (i) and (ii)

      K2K=195T

         T = 390 K

          in °C, 390 – 273 = 117°C