A gas is heated at a constant pressure. The fraction of heat supplied used for external work is

first law of thermodynamics is dQ = dU+dW---(1) dQ=nCPdT dU=nCVdT ;       CPCV=γ ⇒ CPγ=CV  substitute in eqn(1) nCPdT=nCPγdT+dW nCPdT(1-1γ)=dW dQ(1-1γ)=dW (1-1γ)=dWdQ=fraction of heat supplied used for external work