5.1 Thermal Physics Flashcards
Define thermal equilibrium (2)
No net transfer of thermal energy
Any objects in thermal equilibrium are at the same temperature
What is the triple point?
One specific temperature at which all three phases of matter of that substance exist in thermal equilibrium
What is the zeroth law of thermodynamics?
If two objects are each in thermal equilibrium with a third then all three objects are in thermal equilibrium with each other
Kinetic model - solids (3)
Regular arrangement of atoms or molecules, packed closely together
Strong electrostatic forces of attraction between atoms or molecules
The atoms vibrate about their fixed positions
Kinetic model - liquids (3)
Atoms or molecules are close together
More kinetic energy than in a solid
Atoms or molecules can change position and flow past each other
Kinetic model - gases (4)
Atoms or molecules much further apart
More kinetic energy than liquids
Negligible electrostatic forces between atoms or molecules
Move randomly with different speeds in different directions
What is Brownian motion?
The random motion of microscopic particles in a fluid as a result of their collisions with molecules in the medium
What is the smoke cell experiment? (2)
Smoke is trapped in a smoke cell by a cover slip and placed under a microscope
The smoke particles move as the air molecules collide with them and reflect the light
Define internal energy
The sum of the random distribution of kinetic and potential energies associated with the molecules of a system
What is absolute zero? (2)
The lowest limit for temperature
The temperature at which a substance has minimum potential energy
Why is internal energy not zero at 0K?
The substance still has electrostatic potential energy stored between the particles
What happens to energy as temperature increases? (2)
Increases kinetic energy
Increases internal energy
What happens during a phase change? (3)
Temperature remains constant
Kinetic energy remains constant
Internal energy changes
Electrostatic potential energy - gases (2)
0J
Negligible electrical forces between atoms or molecules
Electrostatic potential energy - liquids (2)
Negative value
Energy must be supplied to break the bonds
Electrostatic potential energy - solids
Large negative value
Define specific heat capacity
The energy required per unit mass to change the temperature by 1K
How is specific heat capacity determined? (3)
The energy transferred by an electrical heater is equal to the energy put into the material
Record the time the heater is on for and the temperature change
Use E = IVt and E = mcΔθ to get c = (IVt)/mΔθ
What is the method of mixtures? (2)
Known masses of two substances at different temperatures are mixed together
At thermal equilibrium, they are at the same temperature so the specific heat capacity of one can be determined if the SHC of the other is known
Define specific latent heat
The energy required to change the phase per unit mass while at a constant temperature
What is specific latent heat of fusion?
The energy required to change a substance from a solid to a liquid
What is specific latent heat of vaporisation?
The energy required to change a substance from a liquid to a gas
How is specific latent heat of fusion of ice determined? (4)
Use a thermometer to ensure the ice is at its melting point at the start of the experiment
Use an electrical heater to determine the input energy; E = IVt
Measure the mass of melted ice after a given time, t
Use L = E/m to determine the specific latent heat of fusion
How is specific latent heat of vaporisation determined? (3)
Use an electrical heater; E = IVt
Use a condenser to collect and measure the mass of liquid that changes phase
L = IVt/m
Why is latent heat of vaporisation usually much higher than latent heat of fusion?
There is a much bigger difference between the internal energies of liquids and gases, compared to solids and liquids
What assumptions are made in the kinetic model for ideal gases? (5)
A gas contains a large number of atoms or molecules moving in rapid, random motion
The volume of particles in the gas is negligible compared to the volume of the container
The collisions of atoms or molecules with each other and the container walls are perfectly elastic (no KE lost)
The time taken for collisions is negligible compared to the time between collisions
Intermolecular forces between the particles are negligible except during collisions
What is Boyle’s Law?
At a constant temperature, pressure is inversely proportional to volume
What is the pressure law?
For a constant mass and volume, absolute temperature is directly proportional to pressure
What is Charles law?
For a constant mass and pressure, absolute temperature is proportional to volume
How can absolute zero be estimated? (3)
Use air sealed in a container and submerged in a water bath
Increase the temperature of the water bath and record the change in pressure of the air with the changing temperature.
Plot pressure against temperature (°C) and extrapolate the straight line back to the x-intercept as at absolute zero the particles are not moving so pressure is zero
Why is rms speed used used instead of average velocity of particles in a gas?
As velocity is a vector, the average velocity would be 0 ms^-1
How is rms speed calculated? (3)
Square the velocities of the particles
Take the mean average
Square root the mean
How is the Boltzmann constant calculated?
R / Avogadro’s constant
How is absolute temperature and kinetic energy of a ideal gas related?
Average KE of an individual molecule in an ideal gas is directly proportional to the absolute temperature of the ideal gas
How does mass affect the speed of gas particles at the same temperature? (2)
Different gases at the same temperature have the same kinetic energy
This means lighter particles must be moving much faster
What is the internal energy of an ideal gas? (2)
The sum of kinetic energies of the particles in the gas
There is no potential energy because the electrostatic attraction between particles is negligible
