first law of thermodynamics,

1. FIRST LAW OF THERMODYNAMIC &
ZEROTH LAW
PRESENTED BY;
GAURAV POUDEL ABHISHEK KUMAR
11195121 11195151

2. THERMODYNAMICS
 Thermodynamics is a branch of science.
 Concerned with heat and temperature and their relation to energy and work .
 In particular , it describe how thermal energy is converted to and from other
forms of energy and how it affects matters.

3. FIRST LAW OF THERMODYNAMICS
This law may be stated as follow;
A) “The Heat and Mechanical Work are mutually convertible”.
According to this law, a definite amount of mechanical work is
needed to produce a definite amount of heat and vice versa.
i.e work is directly proportion to the heat transfer.
dW dQ
B) “The energy can neither be created nor destroyed though it can be
transformed from one form to another “
When a system undergoes a change of state then both heat transfer
and work transfer takes place. The net energy stored within the system and is
known as stored energy or total energy.

5. This means , the amount of heat given to the system is equal to the sum increase
in the internal energy of the system and the external work done .
 Heat/work formula ; U = Q - W
dU = Q – PdV [W= PdV]

6. SIGN CONVENTION OF HEAT AND WORK

7. Significance of first law of thermodynamics
 The relation between heat and work is establissed by the first law of
thermodynamics.
 Both Work and Heat are equivalent to each other.
 The exact equivalent amount of energy of the surrounding will be lost
or gained , if any system gains or losses energy.
 Applied heat is always equal to the sum of work done and change in
internal energy.
 Energy is constant for an isolated system.

8. Application of first law of thermodynamics
 Heat engine
The heat engine is the most common practical application of the
First Law. Thermal energy is converted into mechanical energy via heat
engines and vice versa. The vast majority of heat engines are open systems.
 Refrigerators, air conditioners, and heat pumps
Refrigerators and heat pumps are mechanical energy converters
that convert mechanical energy to heat.
 Melting process: When a solid melts to liquid, its internal energy
increases. Let m = mass of liquid and L = latent heat of the solid. Amount
of heat absorbed by the system, dQ = mL.
A small amount of expansion occurs, i.e., ΔV = 0
so,

9. dQ = dU + dW
⇒ dU = mL
Thus, internal energy increases during the melting process.
 Isothermal process:
The temperature of an ideal gas remains constant during an
isothermal process. This means that the heat supplied to the system is
utilized to do work against the environment. So,
dQ = dU + dW
⇒ dQ = dW

10. Joules setup to validate first law

11. ZEORTH LAW OF THERMODYNAMICS

12. Application of
Zeroth Law of
thermodynamics.
1. A cup of hot tea, when left
open, cools eventually. Tea
loses its heat to the
surroundings. Eventually, it
attains thermal equilibrium
when the temperature of
surroundings becomes equal to
the temperature of the tea, as
suggested by the zeroth law of
thermodynamics..

13. 2. Mercury thermometer works on the zeroth law of thermodynamics. The mercury
in the tube expands, and the height of the mercury level increases as the
thermometer is placed over a hot surface, indicating the increased temperature.
3. A cold glass of water eventually cools down.
4. Fruits and vegetables kept inside the refrigerator achieve the fridge’s
temperature when kept inside over a long time.

14. THANK YOU