FIRST LAW OF THERMODYNAMICS EXPLAINED !!

The First law of thermodynamics states that energy is neither created nor destroyed. Thus the total energy of the universe is a constant. However, energy can certainly be transferred from one form to another form.

The 1^st law of thermodynamics can be mathematically stated as follows:

§dQ (HEAT) = §dW (WORK)

During a thermodynamic cycle, a cyclic process the systems undergoes, the cyclic integral of heat added is equal to integral of work done. The first law equation can also be written in the form,

§(dQ – dW) = 0

Equation dU = dQ – dW is a corollary to the first law of thermodynamics. It shows that there exists a property internal energy (U) of the system, such that a change in its value is equal to the difference in heat entering and work leaving the system.

Another property named enthalpy (H) can also be defined now as a combination of properties U, p and V.

H = U + pV

For a reversible process, since dW = pdV, the first law of thermodynamics can also be written as

dQ = dU + pdV