Thermal Physics Flashcards
Define internal energy
The sum of the randomly distributed kinetic energies and potential energies of the particles in a body
When is the internal energy of a system increased
When energy is transferred to it by heating or when work is done on it (& visa versa)
Eg: a qualitative treatment of the first law of thermodynamics
What happens to the particle ensemble during a change in state
The potential energies of the particle ensemble are changing but not the kinetic energies
What is the formula for a change in state
Q = ml
Where L is the specific latent heat.
What is the proof for existence of atoms
Brownian motion
What is potential energy in particles due to
The separation between the molecules
What is the internal energy of a system determined by
Temperature
Random motion of molecules
The phase of matter - gases have the highest internal energy, solids have the lowest.
Intermolecular forces between particles
(Greater intermolecular forces, higher potential energy)
State the First Law of Thermodynamics
The internal energy of a system is increased when energy is transferred to it by heating or when work is done on it (and vice versa)
1st Law: what happens when a gas expands?
WORK is done BY the gas ON the surroundings
Decreasing the internal energy of the gas
What happens when a gas is compressed
Work is done ON gas BY surroundings
Define specific heat capacity
The amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 °C (or 1 K) without a change of state
How can the specific heat capacity of a fluid be found?
By a CONTINUOUS-FLOW CALORIMETER
Describe the use of a continuous flow calorimeter
A fluid flows continuously over a heating element where energy is transferred to the fluid
- It is assumed that the heat transferred from the apparatus to the surroundings is constant
A fluid flows through an electrical heating wire. The rise in temperature of the fluid is measured using the electric thermometers and is calculated by:
Δθ = T2 – T1
For mass of fluid: flow rate recorded, multiplied bu time taken to give mass of fluid that flows (M1)
The current I and potential difference V are also recorded
The flow rate is then altered to give a mass m2 and the potential difference of the power supply is changed so the temperature difference, Δθ stays the same
The specific heat capacity is found by assuming the thermal losses to the surroundings are constant for both flow rates
Define latent heat
The thermal energy required to change the state of 1 kg of mass of a substance without any change of temperature
What are the 2 types of latent heat
Specific latent heat of fusion (melting)
Specific latent heat of vaporisation (boiling)
Define the specific latent heat of fusion
The thermal energy required to convert 1 kg of solid to liquid with no change in temperature
Define the specific latent heat of vaporisation
The thermal energy required to convert 1 kg of liquid to gas with no change in temperature
What does latent heat of fusion apply to
Melting a solid
Freezing a liquid
What does latent heat of vaporisation apply to
Vaporising a liquid
Condensing a gas
What happens during a change in state
- no change in temperature
- the potential energies of the molecules change, but not their kinetic energies
What does the heat in melting and boiling cause the molecules to do
Move further apart by overcoming the intermolecular forces of attraction
In freezing and condensation molecules move closer together and intermolecular forces of attraction become stronger
As
Kinetic energy is proportional to temp
If no change in tempo, no change in kinetic energy either
Define absolute zero
The temperature at which the molecules in a substance have zero kinetic energy
What does boule’s law state
pressure is inversely proportional to the volume of a gas
State charles’s law
the volume is proportional to the temperature of a gas
At constant pressure
