Thermal Flashcards
What is the kelvin?
Base unit of temperature starting at the lowest possible temperature absolute zero
What is the internal energy of a system?
Energy of molecules due to their individual movements and positions.
Only changes that can cause a change if internal energy of a system are work done or heating.
What can change the internal energy of a system?
Only changes that can cause a change if internal energy of a system are work done or heating.
What is sensible heat?
Energy required to change the temperature of the substance without changing its state.
What is the specific heat capacity of an object?
The energy required to raise 1kg of a substance by 1 kelvin
What happens to the kinetic and potential energies of the molecules upon sensible heating?
The bonds holding the molecules together are broken down decreasing the potential energy as they gain kinetic energy increasing their freedom of movement.
What is latent heat?
Energy required to change the state of a 1kg of a substance
What is the specific latent heat of vaporisation of a material?
Energy required too vaporise 1kg of a liquid at its vaporisation point.
What is the specific latent heat of fusion of a material?
Energy required to melt 1kg of a solid at its melting point.
What is thermal equilibrium?
Any two objects that are at the same temperature, no overall energy transfer
What is the equation relating specific heat capacity (c), Change in energy (ΔQ), mass and Change in temperature (Δθ)?
ΔQ = mcΔθ
What energy changes occur during fusion?
Latent heat is released as a substance solidifies as the molecules slow down (Ep increases and Ek decreases)
What is the equation latent heat (l), Change in energy (ΔQ) and mass?
ΔQ = ml
What energy changes occur during vaporisation?
As a result of an increase in temperature, the kinetic energy of the molecules increases. Due to the increase in kinetic energy, the force of attraction between the molecules reduces as well as the potential energy.
What is sublimation?
Solid that vaporises directly when heated
On a temperature time graph, how can you calculate power?
P = mcΔT / Δt
On a temperature time graph, why does a solid with a larger specific heat capacity have a higher gradient?
The liquid heats up ‘faster’
What is pressure?
Force per unit area exerted normally on a surface in Pascals, Pa
What is Boyle’s law?
For a fixed mass of gas at constant temperature, pressure is inversely proportional too the volume.
What is Charles’ law?
For a fixed mass of gas at a constant pressure, Volume is directly proportional too the temperature.
What is change called if it is made at a constant temperature?
Isothermal
As stated by Charles’ law, Why is the volume directly proportional too the temperature?
When work is done too change the volume of the gas, energy must be transferred as heating in order to remain at a constant pressure.
How do you calculate the work done (ideal gases)?
w = p. ΔV
Why do molecules exert a force o the walls of their container?
Their momenta change as they change direction, N2 a force is exerted on the particles by the wall, N3 the particles exert a force on the wall.
How can a Volume/Temp graph prove the concept of absolute zero?
Extrapolate the graph, it will pass through the x axis at -273.25 degrees Celsius or 0 kelvin
What is the pressure (Gay-Lussac’s) law?
For a fixed mass and volume of gas, Pressure is directly proportional too the temperature.
Why does the pressure law occur?
As the temperature increases, the kinetic energy of the particles increases so there is a larger change of momentum per collision with the container. Impulse increases and so does the force exerted upon the container (hence pressure).
What is an empirical law?
A law determined through experiment
What is absolute zero?
0K or -273.15C
What is an ideal gas?
A gas in which there are no intermolecular interactions so there is no potential energy.
The internal energy is purely kinetic.
Undergo elastic collisions.
What is the equation relating to moles for the ideal gas law?
p.V = n.R.T
What is the equation relating to the number of molecules for the ideal gas law?
p.V = N.k.T
What is the value of boltzmans constant k ?
1.38 x10 ^- 23 Joules per Kilogram
What is the value of the gas constant R?
8.31 Joules per Kilogram per Mole
What is Avogadro’s constant?
6.03x10^23
How do you work out the number of moles given the number of molecules?
n = N/ Avogadro’s
Name 5 assumptions made when modelling the kinetic theory of gases?
1) All gas particles are identical.
2) All collisions are elastic.
3) Particles motion is random.
4) No intermolecular forces.
5) A large (and therefore statistically significant) number of molecules.
6) All particles obey Newton’s laws of motion.
7) The volume of the gas particles is negligible too the volume of the container.
8) Duration of the collisions is negligible compared too the time between the collisions.
What is Brownian motion, and what is the explanation for it?
When viewed under a microscope, pollen grains on water or smoke in the air barrel in unpredictable erratic paths.
Einstein explained this as the larger particles colliding with the water molecules and changing direction.
This provided an explanation for atomic theory.
Why does a gas exert a pressure on its container?
A gas particles momentum changes as they change direction. By N2 a force is exerted by the wall by the particle, by N3 the gas particles exert an equal and opposite force on the wall -> pressure
State any assumption made relating too the motion of a gas in the kinetic theory of gases
All collisions are elastic
Particles motion is random
All particles obey newtons laws of motion
The duration of the collisions is negligible compared too the time between the collisions
State any assumption made relating too the physical properties of a gas in the kinetic theory of gases
All gas particles are identical
No intermolecular forces
Statistically (large) significant number of particles
KINETIC THEORY ONWARDS
What is a change made under constant pressure called?
Isobaric
