Thermal Physics P2 Flashcards
What is the temperature of a gas directly proportional to?
The average kinetic energy of its particles
What is pressure?
The amount of force that an object exerts per unit area
Why do gases exert a pressure on the walls of their container?
Gas particles have momentum and once they collide with a wall their momentum changes. This change suggests they exert a force on the wall which explains how they exert a pressure as pressure is force per unit area.
What is a mole?
1 mole of a thing is 6.02 x 10^23 of that thing
What is the molar mass?
The mass of one mole of a substance
What is molecular mass?
The mass of one molecule of a substance
What is the pressure law?
For any gas of fixed mass and volume, the pressure is proportional to temperature when measured in kelvin
What is Charles’ law?
For any gas of fixed mass and pressure, the volume is proportional to the temperature in kelvin
What is Boyle’s law?
For any gas of fixed mass and temperature, the volume is inversely proportional to the pressure
What is Avogadro’s law?
For any gas of fixed pressure and temperature, the volume is proportional to its moles. Also the volume of 1 mole of gas is same for pretty much all gases
What are the four main reasons why the gas laws break down for real gases?
Real gases can change state, occupy some volume, experience intermolecular forces and collide inelastically
What are the four criteria required for a gas to be an ideal gas?
Never changes state, occupies no volume, has no intermolecular forces and collides elastically with one and other and the walls of the container
What are the three reasons for using ideal gases?
They help us to understand real gases, they make the maths easier and most common gases behave closely to ideal gases at non-extreme temperatures and pressures
What happens to the gas during expansion and compression?
During expansion there is work done by the gas and during compression there is work done on the gas
When the pressure is constant, work done is given by:
W = p x change in volume
How do you find the magnitude of the work done from a p-V graph?
Find the area below the graph
What are the six assumptions that are made for the Kinetic Theory of Gases?
Gases are made up of small particles called molecules where their volume is negligible compared to the volume occupied by the whole gas.
Molecules are continuously moving in random directions and there is no intermolecular forces between molecules therefore they move in a straight line.
They collide with each other and the walls elastically and the time a molecule spends in collisions is negligible compared to the time it spends between collisions.
How do you find the root mean square speed?
Square all of the speeds of the molecules, divide by the number of molecules and then square root the answer.
What are two pieces of evidence which backs up the kinetic theory of gases?
We can derive the ideal gas equation from the kinetic theory equation which provides experimental support.
Brownian motion in smoke particles where air molecules move at random and knock into smoke particles provides evidence of random motion.
How does the kinetic theory of gases explain the pressure law?
When temperature increases molecules move faster therefore more frequent collisions.
This increases the force on the walls as there is a greater change in momentum therefore the pressure increases.
What is heating?
energy transfer due to a temperature difference
What is thermal equilibrium?
when two objects are at the same temperature therefore heating doesn’t occur
What is temperature?
measure of the average kinetic energy of the particles
What is the Celsius and Kelvin scale based off?
Celsius is based off of water and the Kelvin scale is based off the average kinetic energy of particles
What is internal energy?
Sum of the randomly distributed kinetic and potential energies of its particles
What is thermal energy?
Sum of the randomly distributed kinetic energies of an objects particles
What is the change in internal energy equal to?
the energy transfer due to heating + the work done on the system (or - work done by the system)
What is specific heat capacity?
The amount of energy required to raise the temperature of 1kg of a substance by 1K (Without changing its state)
What is latent heat?
Energy transferred during a change of state without changing the temperature
What is the specific latent heat of fusion?
Energy required to change 1kg of material from solid to liquid without a change of temperature
What is the specific latent heat of vaporisation?
Energy required to change 1kg of material from liquid to gas without a change of temperature
How do you find the molecular mass of a substance?
Divide the molar mass by Avogadro’s constant
Why are the ideal gas laws empirical laws?
Because they are based on observations and experiments
How do you find the internal energy of a gas?
The average kinetic energy of the particles multiplied by the number of particles (3/2pV)
