G484 - Thermal Physics Flashcards
One Mole
If you have one mole of any object you have
6.002 x 10^23 of them
Avogadro Constant
6.02 x 10^23
What is the mass of one mole of a substance?
The mass of one mole of a substance is equal to its total atomic mass
Molar Mass
Definition
The mass of one mole of a substance
Molar Mass
Equation
Avogadro Constant x mass of one molecule
Brownian Motion
All gas / liquid molecules are in rapid random motion
Experiment to show Brownian Motion
Pour smoke into a cell and trap with a coverslip
Shine a light through the smoke cell
Observe under a microscope
The smoke molecules reflect the light
The movement of the smoke molecules can be observed
The smoke molecules move the way they do because of collisions with air particles which are undergoing Brownian Motion
What are the five assumptions of kinetic gas theory?
- All collisions are completely elastic
- Gravitational force in molecules is negligible
- No intermolecular forces exist except for when a collision is sustained
- A gas consists of a large number of molecules rapid, random motion
- The total volume of gas molecules is negligible when compared with the volume of the container
What is the kinetic model of gas?
A model which describes the motion of gas molecules
Momentum
Formula
Momentum (kg m/s) = Mass (kg) x Velocity (m/s)
Force Formula (momentum)
Force (N) = ChangeInMomentum (kgm/s) / Time (s)
Why does a gas exert pressure?
Gas molecules are in rapid random motion
A gas molecule collides with the wall of the container
There is a change in momentum meaning that the wall has applied a force on the molecule
As F = (mv-mu) / t
Newton’s third law, every force has an equal and opposite reaction, i.e. the molecule has applied a force to the wall
Sum of collisions over an area = pressure
Therefore P = F/A
More collisions per unit time equals greater pressure
Internal Energy
Definition
The internal energy of a body is the total sum of random distributions of kinetic and potential energies of all molecules in the body
Describe the internal energy of an ideal gas
An ideal gas only has internal energy in the form of random kinetic energy
What is the relationship between temperature and average kinetic energy?
Temperature is proportional to average kinetic energy of a single molecule
How does internal energy vary as water is heated at a constant rate?
Internal energy is always increasing
How does potential energy vary as water is heated at a constant rate?
Potential energy change is greatest when the water is changing state
Potential energy increases slightly as temperature increases
How does kinetic energy vary as water is heated at a constant rate?
Kinetic energy increases when temperature increases
How does temperature vary as water is heated at a constant rate?
While the substance is a solid and heat is applied, the kinetic energy of molecules increases so temperature increases
During a state change the applied heat energy is used to break intermolecular bonds so kinetic energy does not increase so temperature doesn’t either
When the substance is a liquid molecules gain kinetic energy so temperature increases
What is temperature?
The average kinetic energy of a single molecule in a body
Gas Pressure
Equation
1/3 x Nm/V x c²
N = total no. of molecules m = mass of one molecule V = volume of container c = mean speed of a molecule
Or
1/3 x p x c² = 1/3xDensityxMeanSpeedSquared