Thermal Physics

How to convert from Celsius to Kelvin?

+273

Explain thermal equilibrium

Two substances in contact have a net flow of thermal energy from the hotter object to the colder object until they are the same temperature, causing no thermal energy transfer any longer

Explain Brownian motion

The movement of gas particles in random direction and random velocity, due to the collisions with smoke particles in air

Explain internal energy

The sum of kinetic and potential energy

What happens to internal energy whilst changing state?

Kinetic energy remains the same as it is being used to overcome electrostatic bonds, whereas potential energy increases (if solid→liquid→gas)

Define absolute zero

0K, where all molecules stop moving as they have no kinetic energy

Define SHC

Energy required per unit mass to raise the temperature of one kilogram of a substance by one degree

State SHC equation

E=mc∆theta

How can an experiment be carried out to determine SHC

Use an electric heater with known power, for given time, measuring final and initial temperatures. Use equation VI = mc∆theta to find c

Define specific latent heat

Energy required to change the phase of one kilogram of a substance

State specific latent heat equation

E=mL

Explain how an experiment may be carried out for SLH

Use an electric heater of known power, over the time where temperature is not changing measure the time, rearrange E=mL for L

State the formula for number of moles in a substance, n

n = m/M, mass over molar mass (nucleon number)

Name the 5 ideal gas assumptions

• Random motion of atoms

• Attraction between atoms are negligible

• Volume of gas atoms is negligible compared to total volume of gas

• Elastic collisions between other atoms and walls of the container

• Duration of collisions is negligible compared to time between collisions

What is the change in momentum during a collision?

2mv

What is average force on the walls during a collision?

2mv/t

State Boyle’s Law

pV = constant at a constant T

State the pressure law

p/T = constant at a constant V

State Charles’ Law

V/T = constant at a constant p

State ideal gas equation in terms of number of moles

pV = nRT

Explain an experiment for Boyle’s Law

Sealed syringe filled with gas and connected to a pressure gauge, vary the volume of the container and record values of volume and pressure. Plot a graph of p against 1/V

Explain an experiment to estimate absolute zero

place a sealed container of air connected to a pressure gauge in a water bath. Vary temperature and record temp and pressure. Plot pressure against temperature, and extrapolate back to the x-intercept, which is absolute zero.

How do you calculate root mean square speed

Sum the square of all the velocities, divide by number of molecules, and square root

State ideal gas equation using rms

pV = 1/3Nm𝑐²

Explain the Maxwell Boltzmann distribution

Shows the number of molecules with each speed against c, distribution of molecule speeds. The area under represents total number of molecules. As temperature increases, the peak shifts to higher speed, more spread out distribution

State ideal gas equation in terms of N

pV = NkT

What is the Boltzmann constant derived of?

k=R/N_A

Show how to derive mean kinetic energy of gas molecules

pV = NkT pV = 1/3Nmc²

kT = 1/3mc²

3/2kT = 1/2mc²

E_k=3/2kT

Explain internal energy in terms of an ideal gas

As there is no electrostatic forces between molecules, there must be no potential energy.

Explain the kinetic model in solids

• atoms closely packed together

• strong electrostatic forces

• vibrate around fixed positions

Explain the kinetic model in liquids

• greater separation than solids

• weaker electrostatic attraction

Explain the kinetic model in gases

• atoms move freely and rapidly

• molecules of random speed and direction

• electrostatic attraction is negligible

State the formula for number of moles with avogadros number

n = N/Na