Thermal Physics

What does temperature measure?

The average kinetic energy of the particles in a substance.

What are the fixed points of the Celsius scale?

0°C (melting point of ice) and 100°C (boiling point of water) at atmospheric pressure.

What are the fixed points of the thermodynamic scale?

Absolute zero and the triple point of water (273.16 K).

What is the SI unit of temperature?

Kelvin (K).

What is the equation linking Celsius and Kelvin?

T(K) = T(°C) + 273.16

What temperature is absolute zero in kelvin?

0 K.

What happens to particle kinetic energy at absolute zero?

It is minimal (theoretically zero).

Define thermal equilibrium

When two objects in contact have no net heat transfer.

In which direction does thermal energy flow?

From hotter objects to cooler objects.

Describe particle arrangement in solids

Closely packed in fixed positions.

Describe particle motion in solids

Vibrate about fixed positions.

Describe forces between particles in solids

Strong electrostatic attractions.

Describe particle arrangement in liquids

Close together but randomly arranged.

Describe particle motion in liquids

Move around each other.

Describe forces between particles in liquids

Weaker than in solids.

Describe particle arrangement in gases

Far apart and randomly distributed.

Describe particle motion in gases

Rapid and random in all directions.

How significant are intermolecular forces in gases?

Negligible except during collisions.

What is Brownian motion?

Random motion of visible particles due to molecular collisions.

How can Brownian motion be observed?

Smoke particles viewed under a microscope.

Define internal energy

The sum of kinetic and potential energies of particles.

What happens to kinetic energy when a substance is heated without changing state?

It increases.

What happens to potential energy when a substance is heated without changing state?

It remains constant.

What happens to potential energy during a change of state?

It increases.

Why does temperature stay constant during a phase change?

Energy is used to break intermolecular bonds.

Define specific heat capacity

Energy required per unit mass to raise temperature by 1 K.

What is the equation for specific heat capacity?

E = mcΔθ

What are the units of specific heat capacity?

J kg⁻¹ K⁻¹

What does the method of mixtures assume?

Energy lost = energy gained.

How is electrical energy used to measure SHC?

Energy supplied = VIt.

Why is insulation used in SHC experiments?

To reduce heat loss.

Define specific latent heat

Energy per unit mass to change state without temperature change.

What is the latent heat equation?

E = mL

Define latent heat of fusion

Energy to change solid to liquid.

Define latent heat of vaporisation

Energy to change liquid to gas.

What are the units of latent heat?

J kg⁻¹

What is one mole?

Amount containing 6.02 × 10²³ particles.

What is Avogadro’s constant?

6.02 × 10²³ mol⁻¹

What is the equation for number of moles?

n = m / M

State the ideal gas assumptions

Random motion; negligible volume; elastic collisions; negligible forces.

What causes gas pressure?

Collisions of molecules with container walls.

What is the momentum change in a wall collision?

2mv

State Boyle’s law

p ∝ 1/V at constant temperature.

State Charles’ law

V ∝ T at constant pressure.

State the ideal gas equation

pV = nRT

What is the value of the molar gas constant?

8.31 J mol⁻¹ K⁻¹

How is Boyle’s law investigated?

Using a gas syringe and pressure gauge.

What graph confirms Boyle’s law?

p vs 1/V straight line.

How can absolute zero be estimated experimentally?

Extrapolate pressure–temperature graph to zero pressure.

Define root mean square speed

The square root of the mean of squared molecular speeds.

State the microscopic gas equation

pV = ⅓Nmc²

What does the Maxwell–Boltzmann distribution show?

Number of molecules at each speed.

How does higher temperature affect the MB distribution?

Peak lowers, shifts right, spreads out.

Define the Boltzmann constant

R / NA = 1.38 × 10⁻²³ J K⁻¹

State the ideal gas equation using k

pV = NkT

State the mean kinetic energy equation

Ek = 3/2 kT

How does mean kinetic energy relate to temperature?

Directly proportional to absolute temperature.

What is the internal energy of an ideal gas?

Entirely kinetic energy.

Why do ideal gases have no potential energy?

No intermolecular forces are assumed.