Thermal Physics Flashcards
What is the triple point of a substance
One specific temperature and pressure where the three phases of matter can exist in thermal equilbrium
Define Thermal Equilibrium
No net transfer of thermal energy between the phases
What happens when objects are in thermal equilibrium
There is no net flow of thermal energy between them
What happens when Object A is warmer than Object B
Net flow of thermal energy is from Object A to Object B
Object A gets warmer
Object B gets colder
What is the 0th Law of Thermodynamics
If 2 objects are each in thermal equilibrium with a third, then all three are in thermal equilibrium with each other
What forms the basis of temperature
0th Law of Thermodynamics
What is needed in order to measure temperature
A scale is needed with 2 fixed points at defined temperatures
Describe the Celsius Scale
Freezing + Boiling Points as the 2 fixed points
There are 100 increments between 0 and 100 degrees celsius
Why is the Celsius scale not perfect
Freezing and Boiling Points vary at different atmospheric temperatures
What is the Absolute Temperature Scale also known as
Thermodynamic Temperature Scale
Describe the Absolute Temperature Scale
Uses triple point of pure water and absolute zero
What must any object at 100 degrees celsius be
In thermal equilibrium with boiling water
SI Base Unit for Temperature
Kelvin (K)
Kelvin Formula
Degrees Celsius + 273
What is Kelvin always
Positive
Describe Electrostatic Forces for different phases of matter
Solid - Strong
Gas - Negligible
What does the Kinetic Model describe
How all substances are made up of atoms or molecules - which are all arranged differently depending on the phases of the substance
Density in Water
Less dense in solid than in liquid
One of the rare substances to do this
What is Brownian Motion
The haphazard movement of particles of a substance caused by the transfer of momentum through elastic collisions with particles of a surrounding medium
How Brownian Motion observed
Robert Brown looked through a microscope and recorded his observations of the random arrangement of fine pollen grains floating on water
How did Einstein explain Brownian Motion
In terms of collisions between the pollen grains and millions of tiny water molecules
These collisions were elastic and resulted in a transfer of momentum from water molecules to the pollen grains which made them move in haphazard ways
How can Brownian Motion be observed
Using a smoke cell - particles of smoke are large enough to be seen under a microscope
They move in a random way and are surrounded by air molecules
Air molecules are constantly striking the smoke particles
Air molecules are in random motion
Mean KE of Smoke = Mean KE of air molecules
Air molecules of 500 ms^-1 - Smoke molecules are more massive and move much more slowly
Density for most substances between phases of matter
Most dense in solids
Lease dense in gases
Define Internal Energy
The sum of randomly distributed kinetic and potential energies of atoms or molecules within the substance
Why can the Potential Energy of a Substance never be 0
At 0K there is no kinetic energy but there’s electrostatic potential energy stored between the particles
What happens when a substance reaches its melting or boiling point, while it is changing phase
The energy transferred to the substance does not increase its temperature
EPE of the substance increases as the electrical forces between the atoms or molecules change
When does KE of atoms or molecules increase during phase changes
It doesn’t - potential energy changes
EPE for different phases
Gas = 0J
Liquid = Negative = energy must be supplied to break atomic/molecular bonds
Solid = Large negative
When is EPE lowest and highest
Lowest in Solids
Highest in Gas (0J)
Electrostatic Forces in Gas and Solid
Gas = Negligible
Solid = Large
What is specific heat capacity of a substance
Energy required per unit mass to change the temperature by 1 K
Equation for specific heat capacity
E = mass x specific heat capacity x change in temperature
Experiment for specific heat capacity
Use an electric heater
Insulate surroundings to minimise energy loss
Stir liquid carefully to make sure there is uniform temperature throughout
Specific heat capacity equation with an electric heater
IVt / (mass x change in temperature)
What is specific latent heat of a substance
Energy required to change the phase per unit mass while at constant temperature
Equation for specific latent heat
L = E / m
E is energy supplied to change the phase of mass of the substance
What is the specific latent heat of fusion
Energy supplied to change from solid to liquid phase
What is the specific latent heat of vapourisation
Energy supplied to change the substance from liquid to gas
What graph can be used to give a more accurate value for specific heat capacity
Temperature of the substance against time
Temperature time graph equations
E / change in T = mc x (change in temperature / change in time)
Gradient is change in temperature / change in time
Constant power supplied = E / change in time
Power = mc x gradient
c = P / (m x gradient)
What is the method of mixtures
Another way to determine specific heat capacity
Known masses of two substances at different temperatures are mixed together - recording final temperature at thermal equilibrium allows specific heat capacity of one of the substances to be determined if the specific heat capacity of the other is known
