Suppose you do 100 J of work in compressing a gas. If 80 J of heat escapes in the process, what is the change in internal energy of the gas?

Solution 8E In this process the work was done against the pressure to decrease the volume of the gas. Hence the work was done on the gas and hence there will be no change in internal energy of the gas. Step 1 From the first law of thermodynamics we know that dQ = dU + dW Now, in this process, only energy that was supplied to the gas was the work done on the gas, hence we have dQ = dW Hence we have dU = 0 So, the change in the internal energy of the gas is zero.