Thermal Physics

Molecular properties of solids:

• A regular arrangement of all particles

• Bonded together by electrostatic bonds

• Vibrate in a fixed position

• Not much kinetic energy compared to other states

Molecular properties of a liquid:

• Heating up a solid causes the kinetic energy to break bonds

• This allows molecules to move around and vibrate

• Particle density may slightly decrease

• More kinetic energy than a solid

Molecular properties of a gas:

• Particle density decreases by a factor of 10 in each direction

• Hence, they can take up the space of a container and be compressed

• More free to move with lots of kinetic energy

Brownian motion practical:

• Particles of smoke are large enough to be seen under a microscope moving randomly

• The random motion is caused by air molecules striking the smoke particles, of which are also in random motion

Triple point

• On a pressure temperature graph, there exists a point where matter can be all 3 states

• Can only exist in 1 temperature

Absolute zero

• The temperature where a substance has minimum internal energy

• Particles are theoretically stationary at this temperature

• 0K

Triple point of water (temperature)

0.01°C = 273.16K

Kelvin

• Absolute temperature scale from absolute zero to the triple point of water

• 0K - 273.15K

0th law of thermodynamics

If two objects are in thermal equilibrium with a third, then all three are in thermal equilibrium

Internal energy formula:

The sum of all randomly distributed kinetic energy and potential energy in a system

Phase change

• When a substance changes state, a phase change occurs

• The internal energy increases but the temperature stays constant

Temperature against potential energy graph

Specific heat capacity of a substance

The energy required per unit mass to change the temperature by 1K

Specific heat capacity equation:

• c = E/(mΔθ) implies E = mcΔθ

• c = specific heat capacity

• E = energy supplied to the substance

• Δθ = change in temperature

How can you determine the specific heat capacity of a substance?

• Use c = IVt/(mΔθ)

Convert kelvin to celcius

K(x) = C(x) + 273.15

Which factors affect the time taken for two objects to reach thermal equilibrium?

The difference in temperature, area of contact and material.

Brownian motion

The random motion of particles suspended in a fluid

Describe the motion of smoke particles

• Particles are always moving

• Moving in random directions

• In a jittery motion

• Follows a zigzag path

Explain the motion of smoke particles

• Air consists of a larger number of molecules which have a small mass compared to the smoke particles

• They are continuously moving randomly, therefore causing elastic collisions

• They have a range of speeds from 0 to high

What are some key features of a graph of temperature against time of a solid being heated up?

• Goes through the origin

• Linear

• Higher gradient means lower specific heat capacity

What happens to the kinetic energy and potential energy as the temperature of a substance increase?

Only KE increases

What happens to the kinetic energy and potential energy as the substance changes state?

Only the potential energy increases

Latent heat of fusion

The energy required to change a solid to a liquid

Latent heats of vaporisation

The energy required to change a liquid into a gas

Compare the typical values of the SHL and SHV of a substance

SHF < SHV

Energy transfers of water being turned into steam, which is used to heat a coffee

Latent heat to condense the steam, energy lost by steam heat the coffee, energy gain by coffee