14 - Thermal Physics Flashcards
What is the triple point of a substance?
A specific heat and pressure where the substance can exist as a liquid, solid and gas without any net transfer of energy, thermal equilibrium.
Describe the energy transfer when a cold object is placed in a warm room.
Thermal energy from the air is transferred to the cold object until they are the same temperature.
What is thermal equilibrium?
When there is no net transfer of energy between two objects because they are the same temperature.
What is the 0th law of thermodynamics?
If two objects are each in thermal equilibrium with a third, they must all be in thermal equilibrium.
How do you convert from Celsius to kelvin?
+-273
What is 0 degrees Celsius?
The freezing point of water.
What is 0 degrees Kelvin?
Absolute zero - the lowest temperature possible in the universe
What is the Kinetic model?
A model which describes how all substances are made up of atoms or molecules which are arranged differently depending on the phase of the substance.
Describe the molecules in a solid.
Regularly arranged
Packed close together
Strong electrostatic forces holding them in place
Can vibrate and have kinetic energy
Describe the molecules in a liquid
Not regularly arranged
Packed close together
Lots of kinetic energy and weaker electrostatic forces allow them to flow past each other and change position
Describe the molecules in a gas
Not regularly arranged
Spread out
Negilible electrostatic forces
Able to move around freely
What causes density?
The size of the space between molecules.
Why is ice less dense than water?
Because when it freezes, the water molecules are held in a structure where they are further away from each other than when they are a liquid.
What is internal energy?
The sum of the randomly distributed kinetic and potential energies of molecules in a substance.
What causes the potential energy of molecules in a substance?
Electrostatic forces between the molecules.
What happens to the kinetic energy of molecules at absolute zero?
There is no kinetic energy
Why is there still internal energy when a substance is at absolute zero?
Because even though the particles have no kinetic energy, they still have potential energy as they are held in place by electrostatic bonds.
What happens to the kinetic energy when an object is heated to its melting/boiling point?
It increases
What happens to the potential energy as an object is heated?
It increases
What happens to the kinetic energy when an object changes state?
Nothing - it stays the same
What happens to the potential energy when an object changes state?
It increases dramatically
Describe the potential energy of molecules in a gas
0 - the highest possible value
Describe the potential energy of molecules in a solid.
large negative value
Why does the kinetic energy of molecules not change when an object is changing state?
Because the energy that is being applied is being used to overcome the electrostatic forces between molecules.
What is the specific heat capacity of a substance?
The amount of energy required per unit mass to change the temperature of the substance by 1 K.
What is the equation for specific heat capacity?
E = mc(delta)T
What is the specific latent heat of a substance?
The amount of energy required per unit mass to change the phase of a substance while at a constant temperature.
Specific latent _____ is when a substance changes from a solid to a liquid.
Fusion
Specific latent _____ is when a substance changes from a liquid to a gas.
Vaporisation
