Question

State the first two laws of Thermodynamics and give a mathematical representation. (Explain the meaning of the symbols)

Answer 1

The first law of thermodynamics states that the total energy of an isolated system remains constant. The law of conservation of energy is a consequence of the fist law of thermodynamics.

Mathematically;

E = constant

E = U + KE + PE = constant

where

E = total energy

U = internal energy

KE = kinetic energy

PE = Potential energy

If the system is not isolated and some work W and heat Q is transferred; then the first law takes the form

ΔE = W + Q

Where

ΔE is the change in total energy

The second law of thermodynamics states that the entropy of an isolated system can never decrease over time. Its either constant (reversible process) or increases (irreversible) with time.

Mathematically;

dS >= dQ / T

where;

dS = infinitesimal change in entropy

dQ = infinitesimal heat change of the system

T = Temperature