The two processes are shown in the following P-V diagram:


             


For iothermal process:

         P₁V₁ = P₂V₂

i.e.,      ${\text{P}}_1=\left(\frac{{\text{V}}_2}{{\text{V}}_1}\right){\text{P}}_2$

For adiabatic process:

            ${\text{P}}_3{\text{V}}_1^{\gamma }={\text{P}}_2{\text{V}}_2^{\gamma }$

i.e.           ${\text{P}}_3={\left(\frac{{\text{V}}_2}{{\text{V}}_1}\right)}^{\gamma }{\text{P}}_2$

As $\gamma >1$, hence P₃ > P₁

Further, as slope of adiabatic curve is greater than that of isothermal process curve, adiabatic curve will lie above the isothermal curve. That is, area under adiabatic curve > area under isothermal curve

i.e., Negative work > Positive work

i.e., W < 0