Unit 2: Thermodynamics

Heat

Heat

Thermal energy is transmitted from one body to another. Heat is energy in transit.

Temperature

It is a measure of an object’s internal energy.

Kinetic Theory of Gases

• It relates to the macroscopic properties of gases such as pressure, temperature, etc.

• Every gas consists of small particles known as molecules.

• The gas molecules are identical but different from those of another gas.

• The volume of molecules is negligible compared to the volume of gas.

• The density of a gas is constant at all points.

• Consequently, pressure is exerted by gas molecules on the walls of the container.

• No attractive or repulsive force exists between the gas molecules.

The Ideal Gas Law

Pv = nRT

• P = pressure

• V = volume

• n = no. of moles

• R = Gas constant

• T = temperature

Average Kinetic Energy

The pressure exerted by N molecules of gas in a container is related to the average kinetic energy.

K avg = 3/2 kb T

• K avg = average kinetic energy

• kb = Boltzmann’s constant

• T = temperature

Root mean square velocity

It gives us a type of average speed that is easy to calculate from the temperature of the gas.

vrms = √3 kb T/ m

• vrms = root mean square velocity

• kb = Boltzmann’s constant

• T = temperature

• m = mass

The Maxell-Boltzmann Distribution

• The Kinetic theory of gases applies to a large number of particles.

• Some molecules will be moving faster than average and some much slower.

Heat Engines

It is a device which uses heat to produce useful work

Convection

The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat

Radiation

Radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium.

Zeroth law of thermodynamics

If objects 1 and 2 are in thermal equilibrium with Object 3, then Objects 1 and 2 are in thermal equilibrium with each other.

First law of thermodynamics

It is a special case of the law of conservation of energy that describes processes in which only internal energy changes and the only energy transfers are by heat and work.

∆ U = Q + W

• Q = heat added

• W = work done by the system

• ∆ U = change in internal energy

work done

it is used to calculate work done.

Isothermal Process

Temperature remains constant.

Adiabatic process

no transfer of heat

Isobaric process

pressure remains constant

Isochoric process

volume remains constant.

Second law of thermodynamics

It describes how systems evolve over time.

Entropy

It is associated with a state of randomness, disorder, or uncertainty.

Conduction

Heat conducts from one point to another only if there is a temperature difference between the two objects.