Thermal Physics Flashcards
What is Internal energy of gas ?
The sum of the randomly distributed kinetic and potential energies of its particles
Absolute temperature scale
K = C + 273
- 0k is lowest possible temperature that any object can theoretically have
(K - Kelvins + C - Celsius)
What happens to the internal energy of a system when energy is transferred to it ?
Increases ( Visa Versa)
- average speed of particles increase
How can (heat) energy be transferred between substances ?
by the collision of particles
What is Specific heat capacity (C) ?
The amount of heat energy required to change 1kg of material by 1 Kelvin
- Measured in JKg-1K-1
- heating will result in a change of temperature
- kinetic energy
Specific heat capacity formula
Q = mcΔt
heat energy = mass x SHC x change in temperature
What is a Continuous Flow (Calorimeter) ?
A fluid flow continuously over a heating element. As its flows, energy is transferred to the fluid.
- Help measure the SHC (change the p.d)
- Q = mcΔt + H ( H is the heat lost to the surroundings)
- random error is fluctuations in temperature of the water flowing in and systematic error is thermometers may not be exactly calibrated
What is Specific latent heat (L) ?
The amount of heat energy required to change the state of 1kg of material
- Measured in JKg-1
- heating will result in change of state
- potential energy
Specific latent heat formula
Q =ml
heat energy = mass x SLH
What are the types of SLH ?
SLH of fusion - solid/liquid transitions
- solid -> liquid = melting
- liquid -> solid = solidifying
SLH of vaporisation - liquid/gas transitions
- liquid -> gas = vaporising
- gas -> liquid = condensing
What is change of state ?
when a substances changes between a solid, liquid and gas. (potential energy of particles changes)
- when the substances changes state, the temperature remains the same as kinetic energy of particles remain the same
- graph (temperature/internal energy)
What is Boyle’s Law ?
ideal gas at a constant TEMPERATURE (K) the pressure and volume are inversely proportional
- p ∝ 1/V (pV = constant)
- graph (pressure/volume) - curve (don’t touch axis’s)
What is Charles’s Law ?
ideal gas at a constant PRESSURE (Pa) the volume is directly proportional to its absolute temperature
- V ∝ T (V/T = constant)
- graph (volume/temperature) - straight line
What is Pressure Law ?
ideal gas at a constant VOLUME (m^3)the pressure is directly proportional to its absolute temperature
- p ∝ T (p/T = constant)
- graph (pressure/temperature) - straight line
Explain Boyle’s Law
- constant temperature = particles speed remain the same
- volume decreased = more collisions per second
- rate of change of momentum increases
- force increases = pressure increases
Explain Charle’s Law
- temperature increases = particles move at a greater speed (more KE)
- to maintain constant pressure = volume must increase
- so longer journey between collisions between particles
- constant rate of change of momentum = constant force = constant pressure
Explain Pressure Law
- temperature increases = particles move at a grater speed (more KE)
- to maintain constant volume = pressure must increase
- particles rate of change of momentum increases
- increases force (on walls) = increased pressure
What is Molecular mass ?
the sum of the masses of all the atoms that make up a single molecule (relative atomic mass)
- e.g. C02 is 12+16+16 = 44
What is the Avogadro constant (NA) ?
is the number pf atoms in exactly 12g of the carbon isotope 12/6 C
- 6.02 x 10^-23 mol-1
- at fixed volume of gas at a fixed temperature and pressure
what is Molar mass of a substance ?
is the mass that 1 mole of that substance would have (equal to its relative molecular mss)
- e.g. helium is 4g because RAM = 4.0
Calculate the number of molecules (N) in a substance ?
N = nNa
- number of molecules = number of moles x Avogadro constant
- number of moles measured in ‘mol’
What is the ideal gas equation ?
PV = nRT
- combine the three laws -> PV/T = constant -> pV/T = nR
(pressure x volume = number of moles of gas x MOLAR GAS CONSTANT x Temperature)
What is the Boltzmann Constant (k) ?
k = R/Na (Boltzmann = Molar gas constant/Avogadro constant) (Na = N/n) -> (Nk = nR) -> pV = NkT
How to calculate WORK DONE on a gas ?
Work done = pΔV
- work done = energy transferred
- constant pressure - Charle’s law
- area under the graph =energy transferred to change volume of gas
Derive the equation for the pressure exerted by an ideal gas ?
1) change in momentum -> mu - (-mu) = 2mu
2) time between collisions -> 2l/u (distance/velocity)
3) force -> mΔt/t -> 2mu/(2l/u) -> mu^2/l
4) pressure = F/A -> mu^2/l^3 -> mu^2/V
(only for one particle)
5) N_u^2 = average
6) total pressure = mu^2/v = Nm_u^2/V
_u^2 =1/3_c^2
EQUATION -> pV = 1/3 Nm_c^2 -> pV = 1/3 Nm (Crsm)^2
_c^2 = Crsm^2 = root mean square speed (typical speed)
Assumptions made in ‘kinetic theory’ ?
- molecules act as point masses ( no volume)
- all molecules of gas are identical
- molecules continually move about randomly
- molecules move in a straight line between collisions
- time of collisions are negotiable (small) compared to time between collisions
- collisions are perfectly elastic (between wall and particle)
How to calculate the kinetic energy of gas molecules ?
1/2m(Crsm)^2 = 3/2kT = 3RT/2Na
- equation made from ideal gas equation and kinetic theory equation
- total kinetic energy - need to know number of molecules e.g. (1/2m(Crsm)^2) x n x Na
What are Empirical Laws ?
are laws based on observations and evidence e.g. the gas laws including the ideal gas law.
- the opposite it theoretical laws - based on theory (predicted and explained) e.g. kinetic theory
How have the behaviour of gases have changed over time ?
at first the three gas laws were developed by a-lot of scientists
- daniel BERNOULLI - explained Boyle’s law
What is the Brownian Motion ?
is the type of movement of any particles suspended in a fluid
- provided evidence for the existence of atoms by noticing pollen grains in water moved with a zig-zag, random motion
- helps the idea that everything is made from atoms
