Enthalpy

Zeroth law of thermodynamics

When two systems A and B are in thermal equilibrium with another system C, the two systems are said to also be in thermal equilibrium with each other.

Volumetric work

This is the work done on a closed system to change the volume.

Work done by the system; there is an increase in volume which shows expansion.

==𝑊 = −𝑝 ∙ ∆𝑉==

Work done on the system; there is a decrease in volume showing compression.

==𝑊 = 𝑝 ∙ ∆𝑉==

Heat

Change in temperature of a system is as a result of work done but can also be as a result of heat exchange. Systems exchange heat and work with the environment but contain thermal energy.

𝐶 = ∆𝑄/∆𝑇

C is heat capacity, Q is heat, T is temperature.

Internal energy

Energy is the ability of a system to give off heat or do work. ==The energy due to kinetic and potential energy of particles of a system is Internal energy, U.==

∆𝑈 = 𝑈𝐴 − 𝑈𝐸

𝑈𝐴 is internal energy at initial state, 𝑈𝐸 is at final state.

Equipartition law

In thermal equilibrium at a certain temperature every degree of freedom(f) has equal energy.

𝐸 = 𝑓/2 ∙ 𝑘𝑇

The degree of freedom of a molecule is the sum of the rotational, translational and vibrational degree of freedom.

Law I of thermodynamics

Law of conservation of energy states that energy can not be destroyed or created.

For a closed system we apply this law:

∆𝑈 = 𝑄 + 𝑊

1st law states that when a system experiences change in state the sum of the energy changes depends only on the initial and final state.

In a system that is;

- Isochoric(constant volume): no work done.

∆𝑈 = 𝑄

- Isobaric(constant pressure): work = –p•∆V

∆𝑈 = 𝑄 –p•∆V

- Isotherm(constant temperature): No internal energy change.

𝑄 = - 𝑊

Enthalpy

This is the sum of change in internal plus work done in an isobaric system.

∆𝑈 = 𝐻

𝐻 = ∆𝑈 + 𝑝 ∙ ∆𝑉