Module 5.1 - Thermal Physics Flashcards by Pavel

What is 0K in degrees C?

0K = -273^C

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What is an advantage of the thermodynamic scale?

(Kelvin scale) It does not depend on the properties of any particular substance

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How do you observe Brownian motion in the lab?

1) Put some smoke in a brightly illuminated glass jar (sealed) and set up a microscope above
2) The smoke particles should appear as bright specks moving haphazardly around when viewed through the microscope

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What is Brownian motion?

Brownian motion is the random zigzag motion of any particle suspended in a fluid.

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How was Brownian motion explained?

Einstein showed this provided evidence for the existence of randomly moving atoms/molecules in the air. The randomly moving particles hit the smoke particles unevenly causing the random motion.

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What is internal energy?

Internal energy is the sum of the kinetic and potential energy of the particles within a system - the amount of energy contained within a system

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What affects the kinetic energy of a particle?

The kinetic energy of a particle depends on its mass and its speed. Average kinetic energy is proportional to temperature

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What affects the potential energy of a particle?

Potential energy is based on the relative positions of particles. Solids have the least whilst gases have the most potential energy.

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What state of matter has the most potential energy?

Gas particles have the most potential energy whereas solids have the least. Gasses actually have 0J potential energy whereas solids have -ive potential energy

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Why does temperature stop increasing during a phase change?

1) The temperature of a substance depends on the kinetic energy of its particles.
2) During a phase change the kinetic energy of the particles of a substance does not change
3) All input energy goes towards breaking bonds between particles and therefore changing their potential energy

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How does internal energy change as a substance is heated (through multiple state changes)?

Internal energy increases linearly as a substance is heated. If there is no phase change occurring it is increasing due to the kinetic energy of the particles increasing. If a phase change is occurring it is due to the potential energies of the particles increasing.

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Describe solids in terms of particles?

Solid - Particles vibrate in fixed positions in a regular lattice. They are held together by strong forces of attraction

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Describe liquids in terms of particles?

Liquid - Particles are constantly moving and free to move past one another but forces of attraction still keep them grouped together

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Describe gases in terms of particles?

Gas - Particles are free to move around with constant random motion. Negligible forces of attraction act between them.

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What is the kinetic model of matter?

Kinetic model of matter - the model of matter where solids liquids and gasses are made up of tiny moving or vibrating particles

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Why is potential energy negative for solids?

Potential energy is negative for solids as energy must be supplied to break molecular bonds

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What is the magic thermal equilibrium law?

If body A and body B are both in thermal equilibrium with body C, then body A and B must be in thermal equilibrium with each other

Define specific heat capacity?

The specific heat capacity (c) of a substance is the amount of energy needed to raise the temperature of 1kg of the substance by 1 K

State the specific heat capacity formula?

E = mcΔθ

Define specific latent heat?

The specific latent heat (of fusion/vaporisation) is the quantity of thermal energy required to change the state (liquid/gas) of 1kg of a substance

State the equation for specific latent heat?

L = E/m
E > Energy change in J
m > mass

What is the latent heat of fusion?

The latent heat of fusion is the energy needed to change between solid and liquid states, breaking the bonds that hold the particles in place.

not to be confused with SPECIFIC latent heat of fusion

What is the latent heat of vaporisation?

The latent heat of vaporization is the energy needed to pull the particles of a liquid apart completely, changing between liquid and gas states.

not to be confused with SPECIFIC latent heat of vaporisation

What are the three gas laws?

Boyle’s Law: pV = constant
Pressure Law: p / T = constant
Charles’s Law: V = kT

State Boyle's Law

At a constant temperature the pressure and volume of a gas are inversely proportional. pV = k

State Pressure Law

At a constant volume the pressure p of a gas is directly proportional to its absolute temperature. For an ideal gas p = 0 at T = -273.15 deg C

State Charles's Law

At a constant pressure the volume of a gas is directly proportional to its temperature

How do you investigate Boyle's Law? (Equipment already set up)

1) Measure the volume of air and pressure when the system is at atmospheric pressure 2) Gradually increase the pressure in regular intervals, writing down pressure and volume of the air 3) Multiplying p and V at any point together should give a constant

How do you investigate Pressure Law? (Equipment already set up)

1) Record temperature of the water and pressure on the gauge 2) Heat the water for a few minutes, stir to ensure uniform temperature. Leave for a bit so air heats up. Record temperature and pressure on gauge 3) Repeat until water boils 4) Repeat twice with fresh cool water 5) Plot graph of p against T and draw line of best fit 6) Can use line of best fit to estimate absolute zero

State the equation of state of an ideal gas

pV = nRT R - Molar gas constant pV = NkT

When does the equation of state work best for real gases?

Low pressures and high temperatures

What is the setup for the Boyle's law investigation?

Sealed measuring tube with air in it and oil at the bottom, a pump and pressure gauge used to increase pressure in the tube

What is the setup for the Determining absolute Zero experiment?

- Sealed flask of air immersed in a water bath. - Flask connected to a pressure gauge - Thermometer in water bath - Heater under water bath

How do you calculate the Boltzmann constant?

k = R/Nₐ

What is the equation linking moles of a substance and particle count

N = nNₐ

Give 4 assumptions obeyed by an ideal gas

1) The gas contains a large number of particles 2) The particles move rapidly and randomly 3) Collisions between particles or particle and wall are perfectly elastic 4) No forces act between particles except in collisions 5) The volume of the particles is negligible compared to the volume of the gas 6) The duration of each collision is negligible compared to the duration between collisions

What four things does the pressure exerted by a gas depend on and why?

Volume - smaller volume, less distance to travel, more frequent collisions Number of particles - More particles, more collisions per second mass - Force is proportional to mass, more force = more pressure speed of particles - faster particles have more momentum so exert more force

Explain pressure

Particles of a gas move around with constant random motion. When a particle hits a wall it exerts a tiny force on the wall and rebounds in the opposite direction. However a gas has millions of particles so a significant number will be colliding with each wall of the container and the collisions will be spread over the surface of the wall. This results in a large combined force - the pressure.

How does the speed distribution of gas particles change as the temperature of the gas increases?

- Average particle speed increases - The maximum particle speed increases - The distribution curve becomes more spread out with a less sharp peak

Derive the equation for kinetic energy of a gas particle?

1) pV = NkT 2) From kinetic theory pV = 1/3 Nmc² 3) Cancel N to get kT = 1/3mc² mc² = 3kT 4) 1/2 mc² is the average kinetic energy of an individual particle so multiply by 1/2 to get: E = 3/2 kT