Thermal Physics Flashcards
What is thermal equilibrium
There is no net flow of thermal energy between phases
What is the kinetic model
A model that describes how all substances are made up atoms or molecules which are arranged differently depending on phase.
How are solids arranged
- Regularly arranged
- Packed closely together
- Strong electrostatic forces holding them in fixed positions
How are liquids arranged
- Atoms or molecules packed closely together
- Have more kinetic energy than solids
- They can change position and flow past each other
How are gases arranged
- Atoms and molecules are much further apart
- Have more kinetic energy than liquid
- Negligible electrostatic forces between them unless they collide
- They move randomly in different directions and speed
Brownian motion
The continuous random motion of small particles suspended in a fluid visible under a microscope
How to observe Brownian motion
By observing smoke particles under a microscope, showing the random movement
What is internal energy
The sum of random distributions of kinetic and potential energies within the molecules in a system
Absolute zero
The lowest limit for temperature (0k), the temperature at which a substance has minimum internal energy
What happens to temperature and internal energy as a substance changes phase
- Temperature remains constant
- There is no change in kinetic energy because temperature is constant during melting
- If a substance is melting potential energy increases and so internal energy increases
As temperature of a body rises how does internal energy change
Internal energy increases
Specific heat capacity
The energy needed to heat a 1kg of mass by 1 kelvin
Determining specific heat capacity
- Place a heater a material
- Heat for a set time recording current and potential difference across the heater using an ammeter and voltmeter
- Measure temperature using a temperature probe
- Plot a temperature time graph
- Where gradient is power/mass x specific heat capacity.
What is specific latent heat
Energy needed to change the phase per unit mass
What is specific latent heat of fusion
When a substance changes phase from a solid to a liquid
What is specific heat of vaporisation
When a substance changes from a liquid to a gas
Determining specific latent heat of fusion
- Place a heater into ice for a set time
- Measure the potential difference and current across the heater
- Collect the melted mass of the ice and find it mass
- Energy/mass melted = specific latent heat of fusion
- E=IVt
Determining specific latent heat of vaporisation
- Place the heater in water for a set time
- Measure the potential difference and current across the heater
- Let the evaporated water to condense and collect the water
- Measure the mass of water
- Specific latent heat of vaporisation = energy/mass evaporated
How to calculate the mass of a molecule
Molar mass/ avogadros constant
Assumptions of the model of kinetic theory of gases
- Large number of molecules in random, rapid motion
- Particles occupy negligible volume compared to the volume of gas
- All collisions are perfectly elastic and the time of the collision is negligible to the time between collisions
- Electrostatic forces between atoms or molecules are negligible except during collisions
What does N stand for?
What does n stand for?
N=number of particles
n=number of moles
Boyle’s law
Pressure is inversely proportional to volume for a fix mass at a constant temperature
Explain in terms of the behaviour of molecules, how a gas exerts a pressure on the wall
- Molecules collide with the wall
- There is a change of momentum of the molecule from the wall
- There is a force exerted on the wall by the molecules and there is a force exerted on the molecules by the wall
- Pressure experience on the wall of force/ area
Gas laws other than boyle’s
Pressure is directly proportional to temperature
Pressure x volume / temperature = constant
Maxwell boltzman distribution
See graph in notes
Calculating absolute zero
- Place a volume of dry air in a flask into a water bath
- Record pressure of air with a pressure gage and temperature of water with a temperature probe
- Plot a pressure temperature graph
- Find the equation of the line
- Substitute y=0 and the solve for x
- Should equal -273k
Investigating boyle’s law
- Attach a pump to a volume scale and a pressure gage
- Record atmospheric pressure and volume
- Pump to change the volume scale
- Slowly decrease pressure changing the volume at intervals
- Plot pressure against 1/volume graph
