First Law of Thermdynamics

First Law of thermodynamics:

Deals with concept of energy conservation (protection) and introduces the concept of internal energy (IE)
Explain Joule's Paddle Wheel Experiment.

Joule observed that:

“During the cyclic process---net amount of heat produced is proportional to the net amount of work done on the system”

∫dQ ∞ ∫dW

In SI system heat & work have same unit thus

∫dQ = ∫dW ∫dQ - ∫dW= 0

∫ (dQ–dW) is same for both systems A & B connecting two state points 1 & 2 in figure.

∫ (dQ–dW) does not depend on paths of process, but depend on point 1 & 2.

Therefore it is point function and hence property of system and overall energy is denoted by E.

E= U+KE+PE, PE is potential energy, KE is kinetic energy, U is Internal energy

Second Law of Thermodynamics:

This law is needed to remove the limitation of first law i.e. as per 1^st law there is no restriction on the direction of flow of heat & work.

e.g. Flywheel on friction braking , brakes get hot as there is loss of KE.

1^st law satisfy that brakes were to be cool and given IE back to wheel for resuming motion again, but this will never occur.

Braking is irreversible process.

1^st law imposes no restriction on flow of heat from lower temperature reservoir to higher temperature reservoir.

The 2^nd law is helpful in following ways:

- It provides means for measuring quality of energy

- Performance of engineering devices i.e. efficiency.

- Determines direction of change for spontaneous process.

- Establishes final equilibrium for spontaneous process.

- Establishes parameters for measuring losses in energy process.

Heat Engine exchanges heat with a single body in equilibrium state and produce work creating any other effect called PMM-2, therefore it follows the “First Law of Thermodynamics” but…………

Fails to conform the “ KELVIN-PLANKS STATEMENT” of 2^nd law.

Hence it is not possible to construct such machine,……..e.g. if condenser is eliminated, simple power plant will be PMM-2.

KELVIN-PLANKS STATEMENT of second law:

It is impossible to construct an engine that operates in a cycle and produces no effect other than work as output i.e. heat is exchanged with a single heat reservoir---means

η = W/Q=1 i.e. efficiency=100% such a system satisfies the principle of energy conservation (First Law), but violates the Kelvin statement of second law i.e. no engine can have 100% efficiency.

Fig

The only alternative is that power output from a heat engine , a portion of heat received must be rejected to heat reservoir(SINK). Engine receives Q1 unit of heat and rejects Q2 unit of heat. Thus coverts (Q1-Q2) heat into work done(WD) per cycle

Fig

Clausius Statement of second law: