Table of Contents

**Energy**:

It is a capacity to perform a work or It is a capacity of system to exert a force for a certain interval. There are two types of energy:

Stored energy | Transient energy |

Energy which remains within a system boundary as an inherent property of system is known as stored energy. | Energy which can cross the system boundary during thermodynamics process is called transient energy. |

It can be defined for state or instant. | It can defined for process. |

They are thermodynamic properties. | They are not thermodynamics properties. |

It is a state or point function. | It is a path function. |

It has a single value at each equilibrium state. | It has not single value at each equilibrium state. |

Cyclic integral is zero. | Cyclic integral is non-zero. |

They are not boundary phenomenon. | They are boundary phenomenon. |

Eg: kinetic energy, potential energy etc. | Eg: heat and work. |

**Internal energy:**

It is a energy of system due to the molecular activity. It can be also defined as it is a sum of molecular potential energy and molecular kinetic energy. It is denoted by U. internal energy per unit mass called specific Internal energy. It is denoted by u and given by : u=internal energy/mass.

**Potential energy:**

It is a energy due to the position of system. It is also defined as energy of system due to its elevation in gravitational field and expressed as: PE= mgz where m=mass, g= acceleration due to gravity and z= elevation of gravitational field.

Kinetic energy:

It is a energy of system due to the motion. It is given by:
KE= 1/2mv^{2}.

**Total energy:**

It is sum of internal energy, potential energy and kinetic energy. It is given by:

E=U+KE+PE

E=U + 1/2mv^{2} + mgz

Specific total energy

E=u + 1/2v^{2} + gz

**Energy
transfer**:

There are two types of energy transfer which are given below:

**Heat transfer:**

It is a transfer of energy without transfer of mass due to the temperature difference is called heat transfer. It is denoted by Q and its si unit is joule ( J ).

Sign convection for heat transfer: heat transfer from surrounding to system is taken as positive and from system to surrounding is taken as negative.

**Work transfer: **

It is a transfer of energy without transfer of mass due to the any property difference except temperature difference. It is denoted by W and its si unit is joule ( J ).

Sign convection for work transfer: work done by the system is taken as positive but work done on the system is taken as negative.

**Similarities of work and heat transfer:**

- Both are forms of energy and transient types.
- Both are not thermodynamic properties.
- Both are path function.
- Both are boundary phenomenon.
- Both have same unit joule.
- Cyclic integral is not zero.

**Difference between work and heat transfer:**

Work transfer | Heat transfer | |

1 | It is a transfer of energy but not mass due to the any properties difference except temperature difference. | It is a transfer of energy but not mass due to the difference of temperature. |

2 | It is a high grade of energy. | It is a low grade of energy. |

3 | It is a organized form of energy. | It is unorganized form of energy. |

4 | For displacement work, movement of piston is required. | Movement of piston is not required. |

5 | Work done from the system is positive and to the system is negative. | Heat transfer from the system is negative and to the system is positive. |

6 | Area under P-V diagram. | Area under P-T diagram. |

**Expression of displacement work transfer:**

Consider a piston cylinder device containing a gas as shown in fig 1 . If piston is moves small distance dl by using a force F then work done for process 1-2 is given by:

**Constant volume process**

**Constant pressure process:**

**Constant temperature process:**

**Polytropic process:**

The process which fallowed the relation PV^{n} = constant called polytropic process. The
different process is depend on the value of n. so it is given below:

Value of n | equation | process |

0 | P = constant | Constant pressure or isobaric |

1 | PV = constant | Constant temperature or isothermal |

∞ | V = constant | Constant volume process or isochoric |

γ |
PV^{Y} = constant
| Adiabatic |

Work done in polytropic process:

The equation is applicable if n is not equal to 1.

**Note: work done due to spring = 1/2KX**^{2}