Thermal Physics Flashcards
What is thermal equilibrium?
When 2 substances in physical contact with each other no longer exchange any heat energy and both have reached an equal temperature
What are the energy transfers when thermal equilibrium is reached?
There are none - energy is no longer transferred between the regions
How is thermal equilibrium reached?
The hotter region will cool down and the cooler region will heat up until they reach the same temperature.
What is the absolute scale of temperature?
The thermodynamic scale that does not depend on the property of any particular substance
What is the scale for absolute temperature of water?
What is the triple point of pure water?
The point where pure ice, pure water and pure water vapour can all exist at the same temperature and pressure
What temperature scale is used in thermodynamics?
The Kelvin scale
What is the freezing point of water?
0 degrees Celsius
What is the boiling point of water?
100 degrees Celsius
How do you convert from Celsius to kelvin?
Add 273
What is the particles arrangement of a solid?
Fixed pattern - lattice structure
What is the particles arrangement of a liquid?
Random
What is the particles arrangement of a gas?
Random
What is the space between particles like for a solid?
No space
What is the space between particles like for a liquid?
Some space
What is the space between particles like for a gas?
Large space
What are the intermolecular forces for a solid?
Strong
What are the intermolecular forces for a liquid?
Weak
What are the intermolecular forces for a gas?
Negligible
What is the particle movement like for a solid?
Vibrate about a fixed position
What is the particle movement like for a liquid?
Flow past each other
What is the particle movement like for a gas?
Move around at different speeds
What is the potential energy for a solid?
Low
What is the partial energy for a liquid?
Medium
What is the partial energy for a gas?
High
What is the substance shape of a solid?
Fixed
What is the substance shape of a liquid?
Not fixed
What is the substance shape of a gas?
Not fixed
What is the substance volume of a solid?
Fixed
What is the substance volume of a liquid?
Fixed
What is the substance volume of a gas?
Not fixed
What is the substance density of a solid?
High
What is the substance density of a liquid?
Medium
What is the substance density of a liquid?
Medium
What is the substance density of a gas?
Low
What are the particle arrangement for the 3 main states?
What is Brownian motion?
Small particles suspended in liquid or gas are observed to move around in a constant, random motion
What does Brownian motion provide evidence for?
The existence of molecules in a gas or a liquid
How can Brownian motion be observed?
In a smoke cell
How can a smoke cell be observed to prove Brownian motion?
In Brownian motion, what do collisions between the small and large particles do?
Cause the larger particles to change their speed and direction randomly
How are smaller particles able to change the direction and speed of larger particles randomly?
- They are travelling at a much larger speed in comparison to the large particles
- They have a lot of momentum, which they transfer to the larger particles when they collide
What is internal energy?
The sum of randomly distributed kinetic and potential energies of atoms or molecules within a substance
What is the internal energy of a system defined by?
- Temperature
- The random motion of molecules
- The phases of matter
- The intermolecular forces
How does temperature affect internall energy?
- Higher temperature means greater KE, so greater internal energy
- Lower temperature means less KE, so lower internal energy
How does phase of matter affect the internal energy?
Gases have the highest internal energy, solids have the lowest
How do intermolecular forces affect internal energy?
- Stronger intermolecular forces have higher potential energies
- Weaker intermolecular forces have lower potential energy
How is internal energy increased?
- Doing work on it
- Adding heat to it
How is internal energy decreased?
- Losing heat to its surroundings
- Changing phase from a gas to a liquid or a liquid to a solid
What is absolute zero?
The temperature at which the molecules in a substance have 0 kinetic energy = 0 kelvins
Is it possible to have a temperature lower than 0K?
No - for a system at 0 K it is not possible to remove any more energy from it
What is internal energy directly proportional to?
Temeperature
What happens when a substance reaches a certain temperature and KE stops increasing?
The energy will go into increasing its electrostatic potential energy
What does electrostatic potential energy do to molecules?
Breaks their bonds apart, causing them to move further apart and change state
What happens when a substance changes its state from solid to liquid or liquid to gas?
- The electrostatic potential energy of the molecules increases
- The bonds between molecules break and the molecules fall apart
- The KE remains the same, meaning the temperature remains the same, despite the substance being heated
What happens when a substance changes its state from gas to liquid or liquid to gas?
- The electrostatic potential energy of the molecules decreases
- Bonds form between molecules and the molecules move together
- The KE remains the same, meaning the temperature remains the same, despite the substance being heated
What are the electrostatic forces & electrostatic potential energy values like for a solid?
Very large electrostatic forces so a largely negative electrostatic potential energy
What are the electrostatic forces & electrostatic potential energy values like for a liquid?
Electrostatic forces that are small but present so a small negative electrostatic potential energy
What are the electrostatic forces & electrostatic potential energy values like for a gas?
Negligible electrostatic forces so 0 electrostatic potential energy
What is specific heat capacity?
The amount of thermal energy required to raise the temperature of 1kg of a substance by 1K
What is SHC measured in?
Joules per kilogram per kelvin
J kg^-1 K^-1
What does the definition of SHC show?
- The greater the mass of the material, the more thermal energy that will be required to raise its temperature
- The greater the change in temperature, the higher the thermal energy required to achieve this change
What does it mean if a substance has a low SHC?
It heats up and cools down quickly
What does it mean if a substance has a high SHC?
It heats up and slows down slowly
What is the specific heat capacity equation?
E = mcΔθ
E = change in thermal energy, J
c = specific heat capacity J kg^-1 K^-1
m = mass, kg
Δθ = change in temperature, K
How can you determine the SHC of a solid?
How can you determine the SHC of a liquid?
What may lower the efficiency in the SHC experiments?
- Not all of the heat will supplied by the heater will go into the substance - some heat will go to the surroundings, meaning the value of energy supplied will be too large so the SHC value determined will be greater than expected
- There may be fluctuations in power supply - take several periodic measurements of the voltage and current and calculate the averages
What is the specific latent heat of fusion?
The thermal energy required to convert 1kg of a solid to liquid with no change in temperature
What is the specific latent heat of vaporisation?
The thermal energy required to convert 1kg of liquid to gas with no change in temperature
What is the specific latent heat equation?
E = mL
E = amount of thermal energy, J
m = mass, kg
L = specific latent heat, J kg^-1
What is the difference in energy required to melt ice and energy required to boil water?
- For melting ice, energy is required to increase the molecular separation until they can flow freely over one another
- For water boiling, energy is required to completely separate the molecules until there are no longer forces of attraction between the molecules
The energy required to boil water is much greater
How can you determine the specific latent heat?
What is one mole?
The SI base unit of ‘amount of substance’. It is the amount containing as many particles as there are atoms in 12g of carbon-12
What is avogadro’s constant?
The number of atoms in 12g of carbon-12
What is avogadro’s constant value?
6.02 x 10^23 mol^-1
What is the avogadro’s constant equation?
N = n x Na
N = number of molecules
n = moles
Na = avogadro’s constant
What is the mass and molar mass equation?
n = m/ Mr
n = moles
m = mass (g)
Mr = molar mass (g mol^-1)
What are the model of kinetic theory of gases assumptions?
- There is a large number of molecules in random rapid motion
- Particles occupy negligible volume compared to the volume of the container
- All collisions are perfectly elastic
- The time of a collision is negligible compared to the time between collisions
- There are negligible forces between particles (except during collision)
What is pressure in a gas due to?
Collisions of the gas particles with the walls of the container that holds the gas
What happens when a gas particle hits the wall of the container?
It undergoes a change in momentum due to the force exerted by the wall of the particle
Whats the equation for the force exerted by the wall on the particles in the container?
Initial momentum = mv
Final momentum = -mv
Δp = -2mv
-F = Δp / Δt = -2mv / Δt
F = 2mv/ Δt
What is the ideal gas equation?
pV = nRT
p = pressure (Pa)
V = volume (m^3)
n = num of moles (mol)
R = molar gas constant = 8.31 J kg^-1 K^-1
T = temperature (K)
What is the second ideal gas constant?
pV = NkT
p = pressure (Pa)
V = volume (m^3)
N = number of molecules
k = boltzmann constant = 1.38 x 10^-23 J K^-1
T = temperature (K)
What is Boyle’s law?
Pressure of a gas is inversely proportional to the gas’s volume
What are the Boyle’s law equations?
p ∝ 1/ V
pV = constant
p1 V1 = p2 V2
initial final
What is the pressure law?
The pressure of a gas is directly proportional to it’s temperature
What are the pressure law equations?
p ∝ T
p1 / T1 = p2 / T2
P / T = constant
How do you investigate Boyle’s law?
How do you investigate Charles’ law?
How do you investigate the pressure law?
How can you find the value of absolute zero?
From Charles law : if you plot a graph of volume against temperature (in degrees celsius) and extrapolate it back to the x-axis it should meet at -273 degrees celsius. The same applies using the pressure law
What is the main mean square speed equation?
What is the mean speed symbol?
č (c bar)
What is the mean square speed symbol?
č^2
What is the root mean square speed symbol?
sqr(č^2)
How do you calculate mean square speed?
Squaring all the speeds and finding the mean/average
How do you calculate root mean square speed?
Square rooting the mean square speed
What is the Boltzmann constant equation?
k = R / Na
k = boltzmann constant
R = molar gas constant
Na = avogadro’s constant
What is the value of the molar gas constant?
8.31 J kg^-1 K^-1
What is the value of the Boltzmann constant?
1.38 x 10^-23 J K^-1
How do you derive a new equation from the ideal gas contant equation ,the mean square speed equation and the kinetic energy equation?
What is internal energy?
The sum of all potential and kinetic energies inside a gas
In an ideal gas, what is internal energy due to?
Kinetic energy only - there is so electrostatic potential energy in an ideal gas because the electrostatic forces between particles are negligible (except during collisions)
What is the internal energy equation for an ideal gas?
ΔU = 3/2 NkΔT
