• The portion of the universe selected for study is called the system.

• Rest of the universe other than the portion selected for study is called the environment.

• The surface that separates the system and the environment is called the boundary.

• Systems where there is an exchange of energy, matter and work across the boundary are called open        systems.

• Systems where only energy and work can exchange across the boundary are called closed systems. (i.e.   Boundary is impermeable to matter.)

• Systems where there is no exchange of energy, matter or work across the boundary are called isolated    systems.

• The properties that depend upon the amount of matter are named extensive properties.                              Examples- mass, volume, heat capacity

• The properties that are independent of the amount of matter are named intensive properties.                     Examples : temperature, pressure, density, viscosity, molar volume, molar heat capacity

• Description of the temperature, pressure and composition of the system is called the state of the system. This information is specific for a particular system.

• The properties with specific values for the state in which a system exits are called state functions. These properties do not depend on the history of the system.

• The change in a function of state depends only on its initial state and final state. It is independent of the route followed.

• Volume, temperature, density, refractive index, enthalpy, entropy, etc. are examples for functions of state.

• The quantity of heat supplied to a system or given out from a system under the condition of constant pressure is called the enthalpy change (∆H). This is a thermodynamic property and a function of state.

• The enthalpy change ( ∆H ) associated with a reaction is given by the difference in enthalpy of the products and reactants

ΔH = ΔH_products – ΔH_reactants

Enthalpy change associated with a reaction ; if ∆H < 0 the reaction is exothermic and if ∆H > 0 the reaction is endothermic.

• According to IUPAC convention, enthalpy changes are reported for unit extent of reaction in kJ mol^-1.