3.6.2 Thermal Physics Flashcards
Define avogadro Constant
The number of atoms in 12g of carbon-12 (or the number of molecules in one mole of substance)
What does Boyle’s law state?
The pressure of an ideal gas is inversely proportional to its volume when held at constant temperature.
What is brownian motion?
The random motion of larger particles in a fluid caused by collisions with surrounding particles (e.g. smoke and air)
What does Charles’ law state?
The volume of an ideal gas is directly proportional to its absolute temperature when held at constant pressure.
Define internal energy of a body
The sum of the randomly distributed kinetic energies and potential energies of the particles in a body.
What does the pressure law state?
The pressure of an ideal gas is directly proportional to its absolute temperature, when the volume is fixed.
Define Specific Heat Capacity
The amount of energy required to increase the temperature of 1kg of a substance by 1 Kelvin without changing its state
Define Specific Latent Heat
The amount of energy required to change the state of 1kg of a substance without a change of temperature.
What are the energy changes during a state change?
the (mean/total) potential energy of the system is changing but the (mean/total) kinetic energy is not
2 ways to increase internal energy
- Do work on the system to transfer energy to it
- Heat (increase the temperature) of the system
How to observe Brownian motion
By looking at smoke particles under a microscope
What was Brownian motion used as evidence for?
Existence of atoms
5 assumptions for kinetic theory model
- No intermolecular forces act on the molecules
- Duration of collisions in negligibly in comparison to time between collisions
- Collisions are perfectly elastic
- Molecules move in straight lines between collisions
- Size of gas molecules is negligible
How much potential energy does an ideal gas have?
None (as potential energy is associated with intermolecular forces)
Fundamental difference between gas laws and kinetic theory model?
The gas laws are empirical in nature whereas the kinetic theory model arises from theory
Boyle’s law explanation using kinetic theory model
- If you increase the volume of a fixed mass of gas, its molecules will move further apart
- so collisions will be less frequent
- so force per unit area on surface on container decreases
- therefore pressure decreases
Charle’s law explanation using kinetic theory model
- When the temperature of a gas is increased, the molecules mean kinetic energy increases
- so the molecules mean speed increases
- and because pressure is kept constant (therefore frequency of collisions is constant) the molecules move further apart and volume is increased.
Pressure law explanation using kinetic theory model
- When the temperature of a gas is increased, the mean kinetic energy of the particles increases
- meaning their mean speed increases
- as volume is constant, the frequency of collisions between molecules and their container increases and they collide at higher speeds
- the rate of change of momentum (force exerted on container) increases
- pressure is force / area
- therefore pressure is increased.
Describe how the motion of the atoms changes when a gas’ temperature is increasing
The mean speed/kinetic energy increases
Gas law interpretation of absolute zero
Temperature at which the volume/pressure of a gas extrapolates to zero
Kinetic theory model interpretation of absolute zero
it is the temperature at which the kinetic energy of the particles can be extrapolated to be zero
What do you talk about when using the kinetic theory to talk about P/V in/decreasing?
(Mean/Total) Momentum change!
Rate of collisions!
What is meant by an ideal gas?
- A gas that obeys the ideal gas laws at all temperatures and pressures
What is represented by the area under a pressure volume graph?
The work done to the system
Define the molar mass of a substance
The mass in grams of 1 mole of the substance
How does the arrangement of the atoms change when changing from solid to liquid?
- Some of the atomic bonds are broken
- Allowing atoms to change from vibrating around fixed positions to being able to slide around each other
Does the mark scheme refer to mean or average kinetic energy?
mean
Define internal energy of an ideal gas
The sum of the randomly distributed kinetic energies of the particles in a gas.
