First Law of Thermodynamics
1.0 Introduction
1.0 Introduction
Take a look around your surrounding. You see lots of machines or devices which continuously need mechanical energy. We mainly fulfill this need either by converting electrical energy into mechanical energy like in fan or by converting heat energy into mechanical energy like in a bike. Thermodynamics is concerned with the relationship between heat and work. In this chapter, we will discuss how a gas exchanges energy with surroundings, different types of thermodynamic processes, heat engine, refrigerator and efficiency of a cyclic process. The discipline of thermodynamics arose from the need to understand and improve the working of heat engines.
Thermodynamics:
Thermodynamics is the branch of physics which deals with the interconversion of heat energy and the other form of energy.
Thermodynamical systems (or systems):
A collection of one or more substances on which the effect of the variable such as temperature, volume and pressure are to be studied, is called thermodynamical system.
For example, A gas fitted in a cylinder fitted with a piston is a system.
Surroundings
Everything out side the system, which exchanges energy with the system and which tends to change the properties of the system is called its surroundings.
There are three types of systems:-
Open system: - If there is a free exchange of matter and energy takes place with the surroundings.
Closed system: - If there is an exchange of energy takes place but no exchange of matter takes place.
Isolated system: - If no exchange of matter and energy takes place between system and surrounding.
Thermodynamic variables:
- Composition
- Temperature
- Volume
- Pressure
Thermodynamic state:
The state of a system can be described completely by composition, temperature, volume, and pressure. If a system is homogeneous and has definite mass and composition then the state of the system can be described by using the remaining three variables namely temperature, volume, and pressure.These variables are interrelated by the equation $$PV = nRT$$.
The thermodynamic state of the system is its condition as identified by two independent thermodynamic variables($P$,$V$ or $P$, $T$ or $V$, $T$).
