NEET Chemistry Notes Chemical Thermodynamics-Thermodynamics
Thermodynamics
Thermodynamics
The study of heat or any other form of energy into or out of a system, due to some physical or chemical transformations, is called thermodynamics.
Fundamentals of Thermodynamics
The several terms used in thermodynamics are given below:
System and Surrounding
The region where the observation of transformation of heat and work are made is known as system and the remaining area other than system is known as surrounding.
On the basis of exchange of mass and energy, systems are of three types:
- Isolated System In which neither matter nor energy can be exchanged with surroundings.
- Closed System In which only energy can be exchanged with surroundings.
- Open System In which energy and matter both can be exchanged with surroundings.
Thermodynamic Properties
- Intensive Properties Those properties, that depend on nature of matter but do not
depend on quantity of the matter, e.g. pressure, temperature, specific heat, melting point, etc. \ - Extensive Properties Those properties, that depend on quantity of the matter present in the system, e.g. internal energy, heat, total moles, volume, enthalpy, entropy, free energy, etc.
Force is extensive property but pressure is intensive property.
State and Path Functions
- State Functions The properties which does not depend upon initial and final state of system are known as state functions, e.g. p, V, T, U, G, S, H, etc.
- Path Functions The properties which depend upon path of the system are known as path functions.
e.g. W and q.
Thermodynamic Process
The state of a variable can be changed by means of a thermodynamic process.
These processes are of following types:
- Adiabatic Process In which system does not exchange heat with its surrounding i.e. dQ =0.
- Isothermal Process In which temperature remains ” constant i.e. dT =0.
- Isobaric Process In which change of state is brought about at constant pressure i.e. dp = 0.
- Isochoric Process In which volume of the system remains constant, i.e. dV =0.
- Cyclic Process This is the process in which a system undergoes a number of different states and finally returns to its initial state. For such a process, change in internal energy and enthalpy is zero i.e. dE = 0 and dH = 0.
- Reversible Process In this process, (quasistatic system), change taken place is infinitesimally slow and then- direction at any point can be reversed by infinitesimal change in the state of the system. Reversible process is an ideal process and here, every intermediate state is in equilibrium with others, if any.
- Irreversible Process This process, is the one which cannot be reversed. In this process amount of energy increases.
Concept of Work
- The work has done when gas expands or contracts against the external pressure. Work done is a path function not a state function as depends upon the path followed
- Maximum work done for reversible isothermal process
- where, V2 = final volume Vr = initial volume
- Maximum work done for irreversible isothermal expansion
- If expansion occurs in vacuum i.e. at zero pressure, the value of work done is zero
- For adiabatic change, q = 0
Heat
Heat is defined as the quantity of energy, which flows between system and surroundings on account of temperature difference. It is also a path function, i.e. depends upon the path followed.
It is given as 
Internal Energy (E or U)
It is the sum of all the forms of kinetic and potential energy, i.e. translational, vibrational, rotational energy, etc., associated with the system.
Internal energy is a state function, i.e. it depends only on the conditions of temperature, pressure and volume. It also depends upon the quantity of the matter contained in the system’ internal energy of ideal gases is a function of temperature. Thus, for an isothermal process, 
. Internal energy changes when heat is transferred from – system [i.e. absorption].
