If a gas expands adiabatically. what happens to its temperature? [i mark] (a) increases (b) stay the same rdecreases

Answer : The temperature decreases for an adiabatic expansion process.

Explanation :

As per first law of thermodynamic,

where,

= internal energy

q = heat

w = work done

As we know that, in adiabatic process there is no heat exchange between the system and surroundings. That means, q = constant = 0

For expansion of a gas, the work is to be done by the system. So, 'w' will be negative.

and,

will be also negative. That means,

Or,

From the above we conclude that, the final internal energy will be lesser than the initial internal energy and as we know that, the internal energy is depend on the temperature.

That means, the temperature of the final state will be less than that of the initial state. So, the temperature decreases for an adiabatic expansion process.

Hence, the temperature decreases for an adiabatic expansion process.