5.1 Thermal Physics Flashcards
Thermal Equilibrium
A higher temperature object in contact with a low temperature object will transfer heat from the high temperature to the lower one. The rate of change of temperature will decrease as the objects near each others temperatures, eventually they will effectively be at the same temperature.
Features of the absolute scale of temperature (2)
- Starts at absolute zero
- Not dependent on any physical property of matter
Thermodynamic Scale
Another name for absolute scale
How change in Celsius relates to change in kelvin
They are 1 to 1
Spacing of particles in a solid
Close together (high density)
Spacing of particles in a liquid
Close together (high density)
Spacing of particles in a gas
Sparse (low density)
Motion of particles in a solid
Vibrate around a fixed equilibrium positions but have relatively small motion compared to liquid and gas
Motion of particles in a liquid
Can move past each other but are still attracted
Motion of particles in a gas
Move mostly freely. Almost all kinetic energy is translational (in the form of linear motion)
Kinetic model
Solids, liquids and gases are made up of small moving or vibrating particles
Brownian motion
The random movement of particles
Example of Brownian motion
Observing smoke particles with a bright light and a microscope. They show Brownian motion.
Internal energy
The sum of the randomly distributed kinetic and potential energies of all the atoms and molecules in a system
Feature of 0K in a system
Minimal internal energy
How is internal energy effected by an increase in temperature
increased
Temperature of a substance that is changing state
constant
A substance is heated and begins to melt. What is happening to it’s internal energy as it melts
It increases. (The kinetic energy stays the same but the potential energy increases)
Maxwell-Boltzmann distribution
Graph of number of molecules against speed. Looks kinda similar to a normal distribution with the right side tailing
Specific heat capacity
The energy required to raise 1kg of a material by 1K
Experiment for specific heat capacity
Put the material in an insulator. Heat the material with an electric heater, recording the current and voltage with an ammeter and voltmeter. Record temperature with a thermometer. Once the temperature has changed by 10K calculate the total energy that went in by E = IVt and then calculate c.
Specific latent heat
Energy required to change the state of 1kg of a material
Name for specific latent heat solid->liquid
fusion
Name for specific latent heat liquid->gas
Vaporisation
Equation for specific heat capacity
E = mc(delta t)
Equation for specific latent heat
E = mL
Experiment for specific latent heat of fusion
Fill two funnels with the same mass of ice. Heat one of them with a heater of known power. After 10 minutes compare the amount of water that has dripped out of each one and calculate the difference in mass. Sub into E = mL to get L,
Experiment for specific latent heat of vaporisation
Heat liquid to boiling point in a distilling flask. Condense the vapour given off and then divide the energy put in by the mass of the vapour. (For more accuaracy do this twice with different powers on the heater and then subtract one from the other in order to eliminate heat lost to surroundings)
Model of kinetic theory of gases
Models a gas as a large number of small particles that are in constant motion and behave as an ideal gas
Assumptions for an ideal gas (6)
- Large number of particles
- Particles move rapidly and randomly
- All collisions are perfectly elastic
- Negligible forces between particles except during collision
- Time for collision to happen is negligible compared to the time between collisions
- Particles have negligible volume compared to that of the container
When a real gas behaves like an ideal gas
Low pressure and high temperature
Pressure as a result of a gas
The movement of the individual particles in a gas causes them to collide with the container walls and exerting a force on the walls
Ideal gas equation
pV = nRT p - pressure V - volume n - number of moles R - molar gas constant T - Temperature (kelvin)
Boyles law
Pressure is proportional to 1/Volume
Experiment to investigate Boyles law
Fill a transparent tube with oil. Attach a valve, pressure gauge, scale and pump. Pump air into the system up to a high pressure. Then release a small amount of air and note the pressure from the gauge and the volume from
Experiment to determine absolute zero
Fill a flask with a fixed mass of gas and attach a pressure gauge to the flask. Submerge the flask into water of varying temperature and record the pressure and temperature in each case. Plot a graph of pressure against temperature and it should be a straight line. Continuing the straight line on into the negative celsius it would cross the x axis at absolute zero.
Experiment to determine absolute zero
Fill a flask with a fixed mass of gas and attach a pressure gauge to the flask. Submerge the flask into water of varying temperature and record the pressure and temperature in each case. Plot a graph of pressure against temperature and it should be a straight line. Continuing the straight line on into the negative celsius it would cross the x axis at absolute zero.
Boltzmann constant
R/(NA)
Molar gas constant / Avogadro constant
How to calculate internal energy of an ideal gas
Using the equation for energy of a single particle (E=1.5kT). Multiply by the number of particles
Internal energy of an ideal gas
Equal to the total random kinetic energy (ideal gas has no potential energy)
