LAWS OF THERMODYNAMICS WITH REAL LIFE EXAMPLES

EXPLANATION OF LAWS OF THERMODYNAMICS WITH REAL LIFE EXAMPLES

Students may able to understand three laws of thermodynamics in easy way. Please comment if you enjoyed this content.

TABLE OF CONTENTS

    1. Zeroth law of thermodynamics

    2. First law of thermodynamics

    3. Second law of thermodynamics

            (i) Kelvin Plank Statement

            (ii) Clausis Statement

LAW OF THERMODYNAMICS

There are three laws available in the thermodynamics. They are,
1. Zeroth law of thermodynamics
2. First law of thermodynamics
3. Second law of thermodynamics

1. Zeroth Law of Thermodynamics

This law states that “when two bodies are separately in thermal equilibrium with a third body, then they are in thermal equilibrium with each other”.

Referring the figure, systems A and B are in thermal equilibrium with each other, Systems A and C are in thermal equilibrium with each other when B and C are brought in contact B and C will not undergo any physical changes. Hence B and C are at the same temperature. (i.e) B and C will also be in thermal equilibrium with each other.

Example : Did you know? The application of the zeroth law of thermodynamics is a temperature measurement in any body. For example if you want to measure or body temperature, thermometer undergo thermal equilibrium with our body temperature. So, thermometer works under the zeroth law of thermodynamics.

2. First Law of Thermodynamics

“When a system undergoes a cyclic process, the algebraic sum of the work transfer is proportional to the algebraic sum of the heat transfer”.

Mathematically, ∮ dQ = ∮ dW

In S.I units, the value of J is 1 Nm

ʃdW=ʃdQ or ʃdQ - ʃdW = 0

We know that the law of conservation of energy is defined as "The energy can neither be created nor destroyed, though it can be transformed from one form to any other form"

This law is basic for first law of thermodynamics. According to this law, when the system undergo a process, both heat transfer and work transfer takes place. The net energy transfer is stored within the system

and is known as stored energy (or) total energy of the system

Q = W + ΔU

Example: Let us consider the internal combustion engine. This is a heat engine which converts heat energy into mechanical work. If the heat supplied will be more, work wil be increased. 

3. Second Law of Thermodynamics

The two common statements of second law are

(1) Kelvin plank statement

(2) Clausis statement. 

(1) Kelvin plank Statement 

It is impossible to construct a heat engine working on cyclic process, whose purpose is to convert all the heat energy supplied to it into work.

The above figure Shows a heat engine working on cyclic process it receives heat (Q) from heat source and deliver work equal to the amount of heat received. It is not possible by second law of thermodynamics.

The above figure Shows the possible engine. It receives heat from heat source, a part of heat received is converted into work while the remaining heat is rejected to a lower temperature body known as sink.

Example: Consider the ice cube in a room. Temperature of the environment will be more as compared to ice cube. What will happen? Ice melts and it goes to the liquid state. Here environment gives temperature to the ice cube and it melts. So heat is transferred from hot body to cold body without any external work. But, heat will not be transfer form ice cube to environment.

2) Clausis statement:

It is impossible to construct a system working on a cyclic process whose purpose is to transfer heat from a colder body to a hotter body without the aid of external work,

The above shows the impossible system. Here the heat source is at a temperature T1 and the heat sink at a temperature T2 if T1 > T2 then by clausis statement heat can not flow from lower temperature to higher temperature without the aid of external work.

The above figure shows the possible system, here with the help of heat pump, heat can flow from lower temperature T2 to higher temperature T1.

Example: Consider refrigerator and air conditioner. These devices are works under the clausis statement. Let us consider the refrigerator, temperature inside the refrigerator will be very low as compared to our environment. In a particular region (inside the refrigerator) heat is transferred to environment. You may feel the hot air in the backside of the air conditioner.