Thermodynamics Flashcards
Define Specific Heat Capacity
The amount of energy needed raise 1kg of a material by 1K
Give the equation for specific heat capacity
E = mcT
Define latent heat of vaporisation
The amount of energy needed to change 1kg of a material from a liquid to a gas without a rise in temperature
Define latent heat of fusion
The amount of energy needed to change 1kg of a material from a solid to a liquid without a rise in temperature
Give the equation for latent heat
E = Lm
Define Internal Energy
The internal energy of a system is the sum of the randomly distributed kinetic and potential energies of its molecules
Define Absolute Zero
The kinetic energies of molecules are zero
What is the link between the kinetic energy of molecules and temperature
Proportional as the KE increases, temperature increases
Dervive pV = 1/3Nmc^2
Consider cube of side length, l, containing molecules of mass, m.
A molecule, with velocity, u, in the x-direction. This collides during an elastic collision with the wall. This causes a change in momentum 2mu.
The time between collisions is 2l/u therefore the number of collisions per unit time is u/2l.
According to Newton’s Second Law, force is equal to the rate of change of momentum.
F = 2mu * u/2l = mu^2/l
Force on a wall is the sum of the forces of all particles:
F = m(u1^2 + u2^2+ u3^2…)/l = mN<u>/l</u>
where N is the number of molecules and <u> is mean square velocity in the x direction.</u>
Pressure is F/A. A = l^2 => mN<u>/l /l^2 = mN<u>/l^3
= mN<u>/v</u></u></u>
Overall, velocity of molecules is = <u> + +</u>
Since molecules travel uniformly in all directions. = 3<u> => 1/3 = <u></u></u>
p = mN/3V => pV = mN<u></u></u></u></u></u></u></u></u></u>
State the assumptions for an Ideal gas
Molecules are a negligible size Molecules are identical Collisions are perfectly elastic and the time of collisions is significantly smaller than the time between No intermolecular forces Molecular motion is random
Derive 1/2m = 3/2kT
pV = 1/3Nm pV = NkT
1/3Nm = NkT 1/3m = kT 1/2m = 3/2kT
where 1/2m is the average kinetic energy of the molecules
Define a black body
An ideal body or surface that completely absorbs all radiant energy falling upon it with no reflection and that radiates at all frequencies with a spectral energy distribution dependent on its absolute temperature
Explains what happens with temperature on a radiation curve
Due to the Stefan–Boltzmann law - if you double temperature then area under graph increases by 16 (T^4)
Due to Wein’s Law the peak/max wavelength moves to the left (gets shorter) as temperature increases.
State the Stefan–Boltzmann law
L = 𝜎AT^4 where A is the surface area and T is temperature
State Wein’s Law
λmaxT = 2.9 x 10^-3
