Thermodynamics Flashcards
What is the first law of thermodynamics?
Energy can’t be created or destroyed
dU = dq + dw
What is the second law of thermodynamics?
Entropy of an isolated system always increases
What is the third law of thermodynamics?
Entropy of a system approaches a constant as temperature approaches absolute zero
What is the difference between extensive and intensive variables?
Extensive: Depends on the size of system (n, m, V)
Intensive: Doesn’t depend on size of system (T, P, molar volume)
What is the zeroth law of thermodynamics?
Two systems in equilibrium with a third system ar in thermal equilibrium with each other
What is the ideal gas law?
PV = nRT
What is Dalton’s Law?
Pi = XiP
Partial pressure of one component is the component fraction of the total pressure
What is work? Is it path dependent?
dw = -p_ext * dV
It is path dependent
What is heat?
Quantity that goes in / out of system that changes temperature of the system.
It is also path dependent
What is heat capacity?
C = dq/dT –> how change in heat leads to change in temperature
What is enthalpy?
Change in heat at constant pressure.
q = deltaH = U+pV
What is entropy?
Delta S = integral of dq/T
reversible process = entropy is 0
irreversible process = entropy is less than 0
What is the Carnot Cycle and its efficiency?
E = 1-Tc/Th
Essentially transferring heat from a hot sink to a cold sink and using that energy to do work
Fundamental Equations of Thermodynamics
dU = TdS - PdV
dH = TdS + VdP
dF = -SdT - PdV
dG = -SdT + VdP
What is the point of free energies?
Equations that minimize internal energy and maximize entropy
What is Hemholtz Free Energy?
F = U - TS
relevant for constant T, constant V
What is Gibb Free Energy?
G = U + PV - TS
relevant for constant T, constant P
What is chemical potential?
How G changes when add or subtract certain amount of a component. Driving force of reaction
mu = dG/dn = dF/dn = dH/dn = dU/dn
also thought of as molar Gibbs Free energy
nmu = G
Degree of freedom in phase diagrams?
point = 0df
line = 1df
phase = 2df
What is the Clausius-Clapeyion Equation?
Relates slope of P vs. T phase line with other variables
(dP/dT)_coexist = (Delta S/Delta V) = (Delta H/ T* Delta V)
entropy vs. volume equation more relevant. Think about how changing phases will impact these variables
Why is slope of PvT diagram of water have a negative slope?
From Clausius-Clapeyion, we usually get positive slopes. However, water expands when forming to solid, so slope is negative
What is Gibbs Phase Rule?
F = degrees of freedom - how many variables need to know to define a system
C = number of components
P = number of phases
F = C-P+2
For solids, P not a variable, so
F = C-P+1
What is the Ideal Model for Mixtures? What is the specific Law? Draw it
Both components are non-reacting and non-interacting
Follows Rauolt’s Law: P_A ~ 1-X_A
For when there is liquid phase of A and B, A is volatile and B is non-volatile. What is the vapor pressure of A at different concentrations of B?
Graph: When there is no X_B, vapor pressure of A is P_A*. As we increase B, P_A decreases linearly to 0 at X_B=1
What is the Molar Gibbs Free Energy for an Ideal Mixture?
mu_A = mu_A* + RTlnX_A
When X_A<1, chemical potential decreases, G decreases – this is because there is more entropy in a mixed system
What is the Gibbs Free Energy of Mixing 2 idea solutions of components A and B? What does it look like
DeltaG_mix = nRT(X_AlnX_A + X_BlnX_B)
Curve looks like a U
What is the difference between ideal solutions and non-ideal solutions?
Ideal solutions: A&B don’t interact, don’t see each other
Non-ideal solutions: Interactions between AA, BB and AB
What does “positive deviations” and “negative deviations” mean? What equation is used to determine this?
DeltaU = 2U_AB - (U_AA + U_BB)
Positive deviation = DeltaU > 0, so mixing is not favorable. A and B repulse each other. In P vs. X diagram, curves upward since molecules have increased pressure since they are repulsive
Negative Deviation = DeltaU < 0, A and B have slight attraction towards each other. In P vs. X diagram, curves downward since molecules have decreased pressure since they are attractive
What are the two laws we use at dilute limits in non-ideal solutions?
When X_B –> 1, mostly see other B molecules, so we can model this as ideal. Use Raoult’s Law
P_B = X_BP_B*
When X_B –> 0, We use Henry’s Law. B mostly sees A molecules,
P_B = X_BK_B
K_B depends on if its a positive or negative deviation. KB higher than PB* if positive, lower if negative
What are the 4 Colligative Properties?
- Vapor Pressure Lowering (Roaoult’s Law)
- Boiling Point Elevation
- Freezing Point Depression
- Osmotic Pressure
What is Osmotic Pressure and its equation?
Osmotic Pressure is when you have a channel that is permeable to A and not B, very sensitive measurement that can be used to find molecular weight
Van Hoff Equation: piV = RTn
pi = osmotic pressure
n = moles of B
pi = rhogh
rho = density
g = gravity
h = height the liquid goes
What is the thermodynamic activity?
activity is a measure of non-ideality.
a = P/P*
actual partial pressure / pure partial pressure
for Raoult’s Law, a = X
for Henry’s Law, a = kX
What is the activity coefficient?
activity coefficient = a/X
=1, ideal solution
>1, positive deviation
<1, negative deviation
