Which of the following equations is obtained on combining 1^st and 2^nd law of thermodynamics, for a system of constant mass?

A. dE = Tds - PdV

B. dQ = C_vdT + PdV

C. dQ = C_pdT + Vdp

D. Tds = dE - PdV

Answer: Option A

Solution(By Examveda Team)

By second law of thermodynamics we can write $$TdS = \delta Q$$
Which is valid only for reversiable process but once it is connected to state variable by using first law of thermodynamics we can say it is valid for both reversible and irreversible process and the relation is: $$dU=TdS-PdV.$$