Intro to thermodynamics and kinetics

What is internal energy

The total of the contributions of all the energies. It is impossible to calculate precisely due to the immense number of interactions occurring in a molecule. Energy is hence described in terms of energy changes - i.e. enthalpy is measured as ∆H not just H

Kinetic theory of gases

Gas consists of molecules with mass m and diameter d in constant random motion.

The molecules’ sizes are negligible compared to the distances they move

There are no interactions between molecules besides perfectly elastic collisions

What is temperature

A measure of the amount of energy the particles in a material have

In a gas this is translational, in a solid it is vibrational

Although the velocity of a particle may change due to collisions, the conservation of energy means that the distribution of velocities of all the gas particles is conserved at a given temperature.

What is heat

It is related to temperature. It is a form of energy that can flow between two objects with different temperatures. Heat will flow from the object with the higher temperature to the lower temperature

How is the speed of molecules in a gaseous system distributed

Maxwell-Boltzmann distribution of speeds. The area corresponds to the number of molecules.

(don’t need to remember the equation)

Work

A form of energy. Mechanical work is done when a force moves through a distance.

Work = Force x distance (w = Fd)

distance needs to be in the same direction as force

Work done compressing a gas

Bimolecular vs unimolecular reaction

3 types of system

What restrictions can you put on a closed system

Isobaric - constant pressure

Isothermal - constant temperature

Isochoric - constant volume

Adiabatic - No heat flows between system and surroundings

Letter for internal energy

and heat energy

U

q

Is doing work a positive or negative work energy exchange (w)

Negative.

The work energy change is the change in potential to do work.

What can ∆U be simplified to

∆U = q + w

Reversible processes key concepts

What does dU mean

and d bar

A very small change in internal energy

What is a state function

Can be determined from an instantaneous snapshot of a system.

It does not matter what the initial energetic state was or where the state is going

What is a path function

A parameter tied to a process - heat and work. These are flows of energy and not intrinsic properties of a system so cannot be instantaneously measured.