5.1 - Thermal physics

How to convert celsius to Kelvin?

Add 273, 10 degrees = 283K

Why is the absolute scale used?

0K means particles have minimal internal energy, doesn’t rely on properties of materials such as boiling point

Describe arrangements and energy of states?

Solid - Regular arrangement, vibrate fixed position

Liquid - Close together, constantly moving past each other

Gas - Spaced very far apart, free to move in all directions

What is internal energy?

Sum of all kinetic and potential energies of a system

True or false: At a given temperature, all particles in a material will have the same kinetic energy

False.

Kinetic energies will be randomly distributed around a central ‘most likely’ amount

Explain energy changes that occur during change of state.

During change of state, potential energies of the particles change but kinetic energies doesn’t change

Specific Latent Heat

The energy required to change the state per unit mass of a substance, while keeping temperature constant

What is Brownian motion

The molecules of a gas travel in random directions with random velocities. This is because of their collisions with the molecules in the air resulting in a transfer of momentum in random ways.

Amount of a substance.

Number of particles in a substance can be determined by multiply number of moles by Avagadro’s constant.

Number of moles:

n=m/M, where m = mass of substance and M = Molar mass.

How did Brownian motion give evidence for the particle model of matter?

Smoke particles suspended in the air move in random directions. This must be as a result of collisions with particles making up the air.

In an experiment to find ‘c’ for water lots of energy input escapes. Will this lead to an over or under estimate of SHC?

Overestimate.

Energy input will be used by temperature change will be lower due to escaped energy resulting in an overestimate for ‘c’

What is Avogadro’s constant?

Number of atoms in one mole of a substance.

What are the key assumptions in the kinetic theory of gases?

Large number of molecules in random, rapid motion

Particles are negligibly small compared to total volume of gas

All collisions are perfectly elastic

Time taken for collision is negligibly small compared with time between collisions

Between collisions there are no forces between particles

Why do gasses exert a pressure on the container they are in?

Gas particles collide with surface

Container exerts a force on particles to change their direction, particles exert an equal and opposite force on container

Pressure is force applied per unit area

What is an ideal gas?

A gas where:

• Gas molecules don’t interact with each other

• Molecules are thought to be perfect spheres

What is the ideal gas equation?

pV = nRT

p = pressure, V = volume, n = number of molecules, R = Ideal gas constant, T = absolute temperature

What is Boyle’s law?

Pressure is inversely proportional to volume, providing temperature is constant.

ie - pV is constant

Assuming constant volume, how are pressure and temperature of a gas related?

They’re directly proportional

ie - pT = constant

Use the kinetic theory of gasses to explain why a temperature increase leads to an increase of pressure?

More temperature = more kinetic energy

More kinetic energy = greater change in momentum during collisions with container, also more frequent collisions

Change in momentum is proportional to force applied, and therefore pressure

What equation links N, V, p, m, c?

pV = 1/3Nmc²

p = pressure, V = volume, N= number of particles, c = mean square speed, m = mass of particle

What is meant by the root mean square of speed?

The square root of the mean of the squares of the speeds of the molecules

What does the area under a Maxwell-Boltzmann curve represent?

The total number of particles.

How does the Maxwell-Boltzmann curve change if temperature of a gas is increased?

The average particle speed and maximum particle speed will increase (curve shifts right).

The curve becomes lower and more spread out.

What are the units of the Boltzmann coefficient?

J/K

The average kinetic energy of a particle in an ideal gas is equal to ?

1.5kT

True or false: ‘the internal energy of an ideal gas is proportional to absolute temperature’

True.

In an ideal gas there is no ‘potential energy’ component in the internal energy. This means the internal energy is proportional to the kinetic energy. (which is, in turn, dependent on temperature)