Thermal physics Flashcards
What is potential energy?
The potential energy is a result of the positions of the particles relative to one another and the attractive force between them. The further apart the particles are, the greater their potential energy.
State the first law of thermodynamics and the equation.
The increase in internal energy of a system is equal to the heat energy added to the system minus the work done by the system.
∆U = ∆Q - ∆W
What is meant by thermal equilibrium?
There is no net flow of thermal energy between 2 objects once they are at the same temperature.
Explain what happens to 2 gases at different temperatures when they are mixed and reach thermal equilibrium.
Hot gas molecules transfer energy to cold gas molecules when they collide until all molecules have the same average kinetic energy. Hot gas cools and cold gas heats up until they are at the same temperature.
Why is energy needed to melt ice at 0°C to water at 0°C?
Energy is required to break some inter-molecular bonds increasing the potential energy of the molecules.
Define specific heat capacity
The energy required to increase the temperature of 1kg of a substance by 1°C
Define specific latent heat of vaporisation
The energy needed to change 1kg of a substance from a liquid to a gas with no change in temperature.
Explain what is meant by specific latent heat of fusion
The energy required to change 1kg of a material from solid to liquid without a change in temperature
Explain why the specific latent heat of vaporisation of water is much greater than the specific latent heat of fusion of water.
More energy is required to separate liquid molecules than to break solid bonds. There is a greater change in potential energy when liquid changes to gas than when solid changes to liquid.
Define Avogadro’s constant
The number of molecules in 1 mole of a substance
Why does the pressure inside a football increase when the temperature of the air inside it increases?
When temperature increases, mean kinetic energy of air molecules increases, higher rate of change of momentum when each molecule collides with the inside surface of the football so greater force per collision, more collisions of the molecules with the inside surface of the football per second
Use kinetic theory to explain why the pressure of a gas inside a container increases when its volume decreases.
Smaller volume increases the number of collisions per second of the gas molecules with the walls of the container, rate of change of momentum increases so force on walls increases therefore pressure increases
Explain why the pressure of a gas will decrease when it is released into a container of a greater volume at the same temperature.
When a gas is released into a larger container, the molecules have more space to move around, so they collide with the walls less frequently, resulting in a decrease in pressure.
Describe how the motion of gas molecules can be used to explain the pressure exerted by a gas on the walls of its container.
Molecules collide with walls, the wall exerts a force on the molecules changing its momentum, the molecules exert an equal and opposite force on the wall creating pressure
State two quantities which increase when the temperature of a given mass of gas is increased at constant volume.
Pressure, average kinetic energy of gas molecules
