Thermodynamics

Thermodynamics is a branch of chemistry that deals with energy, its forces & its inter-conversion.

According to law of conservation of energy the total energy change in the universe is constant however it can be converted from one form to another.

The simplest form of energy = Heat.

1. Universe: – Entire part that surrounds us is called universe.

It has two part: System and Surrounding.

System: A part of universe that is under investigation.

Surrounding: The part of universe other than system.

We have 3 basic types of systems:

• Open system: which can exchange energy and matter with surroundings.

For example: A cup with tea.

•  Closed system: which can exchange energy but not matter with surrounding.

For example: Cup of tea with lid.

•  Isolated system: which can neither exchange energy nor matter with surrounding.

For example: Tea in thermos flask.

•  State of the system: The state of the system means the condition of the system which is described in terms of certain observable properties such as temperature, pressure, volume etc.
•  State variables: The properties of the system are called state variables.
•  State function: It is the property that depends upon initial and final states but irrespective of the path followed.

Example : enthalpy etc.

•  Macroscopic properties: They are the properties that depend upon the bulk behaviour that is large number of chemical species.

Example: temperature , pressure etc.

These macroscopic properties are of two types:

• Extensive properties
• Intensive properties
•  Extensive properties: They are those that depend upon the quantity of matter contained in the system not on the nature of substance.

            Example:  internal energy, enthalpy etc.

•  Intensive: They are the properties that do not depend upon the quantity of matter contained in the system but depend upon the nature of substance.

              Example: pH of solution, density, viscosity etc.

•  Please note the ratio of two extensive properties is always intensive.
•  Thermodynamic processes: There are different types of processes :
•  Isothermal: The process that occurs at a constant temperature.
• Adiabatic: The process in which no heat exchange occur.
• Isochoric: The process that occurs at constant volume.
• Isobaric: The process that occurs at constant pressure.
• Reversible process: The process in which all changes occurring in it can be reversed.
• Irreversible process: The process that occurs only in a given direction under a given set of conditions.

In both the cases the total internal energy change and temperature change is same irrespective of the nature of mechanical work.           

• In case of gases mechanical work is given a special name called = P-V work

Consider a cylinder containing gas& is fitted with frictionless piston (no loss of energy)