Thermodynamics Flashcards
Boyle’s Law
p ∝ 1/V
Lussac’s Law
V ∝ T (in K)
Charles’ Law
p ∝ T
The ideal gas Law
pV = nRT
1 bar in Pascals or N m^(-2)
1 x 10^5 N m^(-2)
Converting from °C into K
+ 273.15
For 2 gases A and B, what are their partial pressures?
PA = (nA RT) / V PB = (nB RT) / V
Total pressure = PA + PB
Assumptions for the ideal gas Law
The molecules take up no volume
No interactions between molecules
Van der Waals equation of state and what a and b account for
(nRT / V - nb) - (an^2 / V^2)
a corrects for attractive interactions, which would reduce the pressure from an ideal gas
b corrects for volume of molecules, which would increase the pressure from an ideal gas
ΔU =
Internal energy change
Internal energy =
U(translation) + U(rotation) + U(vibration) + U(electronic)
For an ideal gas we only need to consider U(translation)
The Equipartition principle
for each degree of freedom, we get 0.5kT of energy (0.5 RT per mol)
U = 3/2 R
1st Law of thermodynamics
ΔU = q + w
What does isochoric mean?
Constant volume
–> dV = 0
What does isobaric mean?
Constant pressure (1st law unchanged)
What does adiabatic mean?
No heat change
–> Δq = 0
What does isothermal mean?
Potential and kinetic energy are unchanged
- -> ΔU = 0 for an ideal gas
- -> 𝛿U / 𝛿V = 0 (partial derivatives)
H =
U + pV
2nd Law of thermodynamics
The entropy change of a system and surroundings increases in the course of spontaneous change
ΔS(tot) > 0
Trouton’s Rule
The entropy change when a liquid is vaporised:
Δ(vap)S ≈ 85 J K^-1 mol^-1 for most liquids
Sign of ΔS for solid –> ions
Negative (ions are more ordered)
3rd Law of thermodynamics
A perfect crystal at 0 K has zero entropy
Free energies and when they’re appropriate
Gibbs: G = H - TS (for constant P)
Helmholtz: A = U - TS (for constant V)
dU =
dq + dw = TdS - pdV
