Thermal Physics Flashcards
When does energy transfer between objects take place?
If one object does work on another object or if one object is hotter than another object.
How is the internal energy of an object increased?
Energy transfer by heating or work done on the object.
What does the first law of thermodynamics state?
Change in internal energy = total energy transfer due to heating and work done.
Define internal energy:
The sum of the random distribution of the kinetic and potential energies of its molecules.
Define thermal equilibrium:
when the temperature of 2 objects is equal so no energy transfer takes place.
What is absolute zero?
0K or -273 degrees Celsius. The object has minimum internal energy.
What does temp. rise of an object depend on when it is heated?
The mass, amount of energy supplied and the substance(s) the object is made of.
What is specific heat capacity?
Amount of energy required to raise a unit mass by 1K. JKg(-1)K(-1)
SHC equation?
Q =MC (change in temp)
What experiment can be used to measure SHC?
Inversion tube experiment. Equate gpe to internal energy when it hits the bottom of the tube. Often used with lead. Can also be done by electrically heating a insulated container and equating energy in with rise in temperature recorded by thermometer. Can be done for liquid but must also account for container that the liquid is in.
Give equation for continuous flow heating electrically
IV = mc (change in temp/t)
Which process requires more energy, Vaporisation or melting?
Vaporisation.
Define specific latent heat:
The energy needed to change the state of 1kg of a substance without a change of temperature. Q = mL The unit is J Kg (-1)
Equation for time taken to melt a substance:
t = mL/P
What are the 2 units of pressure?
Pa and N m^(-2)
What angle does pressure act at?
90 degrees to the surface.
What is Boyles Law?
pV = constant. Pressure is inversely proportional to volume.
Why does Boyles Law not work at high pressures?
The particles are so close together that their volume becomes significant which doesn’t obey ideal gas laws.
What is Charles’ Law?
Volume is directly proportional to temperature. V/T = constant.
Equation involving work done, pressure and volume?
W = p * change in volume. This only works when pressure is constant.
What is the pressure law?
p/T = constant
What is Brownian Motion?
Random and unpredictable motion of particles due to collisions with other particles which causes a force into a random direction.
How was Brownian Motion discovered?
Smoke particles were observed under light.
Define the Avogadro constant:
The amount of molecules in 1 mole of a substance or the number of atoms in exactly 12g of Carbon 12.
Define molar mass and its units.
The mass of 1 mol of a substance in kgmol^(-1)
Give the equation relating molar mass, no. of moles and mass.
n = mass/molar mass.
Give the equation relating number of molecules in a substance:
no. of molecules = Na*mass/molar mass
Define ideal gas:
A gas that obeys Boyle’s law.
What is combined ideal gas law?
PV/T =constant. This is only to be used when all 3 are changing.
What is true about ideal gases with equal volumes and equal temperatures?
They have the same number of moles.
What are the units of molar gas constant R?
Jmol^(-1)K^(-1)
What is the ideal gas equation?
pV = nRT
Why does pressure increase when reducing temperature?
There is less distance to travel between collisions so there is more force exerted per second.
How to take root mean square?
square all values, take the mean and then square root the value.
Name 5 assumptions of kinetic gas theory:
1) Volume of molecules is negligible to volume of the gas.
2) There are no forces of attraction.
3) They have random motion.
4) The collisions are all elastic.
5) Time of collision is negligible compared to time between collisions.
Summarise part 1 of kinetic theory derivation:
Change in momentum due to impact is -mv - mv (changes direction hence negative) = -2mv
Time between successive collisions = 2l/v (2l because it travels from one wall then bounces back).
Therefore, F= -2mv/ 2l/v = -mv^(2)/l
Pressure = force/area = mv^2/l/l^2 = mv^2/l^3 = mv^2/V
Summarise part 2 of kinetic theory derivation:
Sum all the pressures together from part 1 and take out factor of m/v so it becomes Nmv^2/V where N is the number of molecules. Since 1/3 particles can be assumed to move in each direction, u, v and w, p = Nm/3V(u^2 + w^2 + v^2) therefore p = Nm/3V(Crms)^2 so pV = 1/3 Nm(Crms)^2
What is the internal energy of an ideal gas equal to?
The kinetic energy.
Why are the gas laws empirical?
They were devised by experiments and observations rather than theory that the kinetic energy formula is derived from.
