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Chemistry GRE > Thermodynamics 2 > Flashcards

Thermodynamics 2 Flashcards

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1
Q

The 2nd Law of Thermodynamics

A

The entropy of the universe tends to increase

S > 0

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2
Q

Entropy

A

dS = dQ/T

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3
Q

S total

A

S total = Ssystem + Ssurroundings

Stotal = dSh + dSc = -Qc/Th + Qc/Tc = Qc(Th-Tc)/Th•Tc

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4
Q

The 3rd Law of Thermodynamics

Nernst heat theorem

A

The entropy S of all perfect crystalline substances is the same at absolute zero

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5
Q

Entropy change at the transition

A

dS = dH/T

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6
Q

Difference in entropy

A

S2 - S1 = dH/T = Cp(dT/T) = Cp(lnT)

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7
Q

Calculate absolute entropy

A

dS = n(Cp/T)dt at constant P

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8
Q

Debye Extrapolation

A

At low T, Cv = Cp = aT^3

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9
Q

Joule’s Law

A

The internal energy of a perfect gas depends only on the temperature

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10
Q

Ideal gasses and solutions

A 
dUt = 0
(dU/dV) = 0
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11
Q

Joule’s Law

A

(dU/dV)t = (dU/dP)t = dU/dT

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12
Q

Gay-Lussac’s law

A

The volume of a given mass of gas is directly proportional to its temperature, if the pressure remains constant

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13
Q

Gay-Lussac’s Law

A

(V2/V1)p = (T2/T1)p

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14
Q

Boyle-Mariotte’s Law

A

The volume of a given mass of gas varies inversely with the pressure, if the temperature remains constant

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15
Q

Endothermic thermochemistry

A

If heat is absorbed during a reaction, dH and dU are positive, and the reaction is said to be endothermic.

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16
Q

Exothermic thermochemistry

A

If heat is given off, dH and dU are negative, and the reaction is exothermic

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17
Q

Hess’s Law

A

If a reaction can be broken down into a number of steps, dH of the overall process is equal to the sum of the enthalpy changes in each step

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18
Q

Standard heat of formation

A

The standard enthalpy of formation of compounds at 1 atm and 25 Celsius, and the substance is in a stable physical state under these conditions. It is 0 for elements

19
Q

Standard enthalpy of reaction

A

The difference in enthalpy beteeen the products and the reactants, when both products and reactants are in their standard state at 298K

20
Q

Gives free energy

A

G = H - TS

21
Q

If dG < 0

A

Then the reaction is spontaneous

22
Q

If dG > 0

A

Then the reaction is not spontaneous

23
Q

If dG = 0

A

Then the system is in a state of equilibrium

24
Q

If dS > 0 & dH <0

A

Spontaneous at all temperatures

25
Q

If dS > 0 & dH > 0

A

Spontaneous at high temperatures

26
Q

If dS < 0 & dH < 0

A

Spontaneous at low temperatures

27
Q

If dS < 0 & dH > 0

A

Nonspontaneous at any temperatures

28
Q

Standard free energy

A

dGrx = sum of dGproducts - sum of dGreactants

29
Q

Chemical potential

A

u = dG/dn
dGb = (u)b•dnb
When phase equilibrium is achieved, the chemical potential of a component is the same in both phases.

30
Q

Gibb’s phase rule

A 
f = c - p + 2
c = # of components in the system
p = # of phases present
f = # of degrees of freedom of a system
31
Q

1 component system Gibb’s phase rule I.e. Pure water
f = 3 - p
If p = 1( the system contains 1 of base), f = 2

A

The system is bivariant

32
Q

1 component system Gibb’s phase rule
f = 3 - p
If p = 2(the system has two phases), f = 1

A

The system is univariant

33
Q

1 component system Gibb’s phase rule
f = 3 - p
If p = 3(three phases), f = 0

A

The system is invariant

34
Q

Bivariant

A

P and T can be modified independently without altering the # of phases

35
Q

Univariant

A

Between two phases on phase equilibria diagram = along the line
For a given temperature, there is only one pressure at which two phases may exist

36
Q

Invariant

A

A point at which all phases are simultaneously at equilibrium aka the triple point no degrees of freedom

37
Q

Colligative properties

A

The physical properties of dilute solutions that depend only on the number of molecules in solution, not their chemical nature.

38
Q

Colligative properties

A

Freezing point depression,
Boiling point elevation,
Osmotic pressure

39
Q

Raoult’s law

A

When a solute is added to a pure solvent, the vapor pressure above the solvent decreases

40
Q

Raoult’s Law

A 
P1 = ix1•P1^o
P1 = vapor pressure of the solvent with added solvent
X1 = mole fraction of solvent
P1^o = vapor pressure of pure solvent
I = # of miles after the solution/# of miles before solution
41
Q

Freezing point depression dTf

A 
dTf = Kf•m(solute)•i 
K = constant
m = mol solute/ kg of solvent
42
Q

Boiling point elevation dTb

A

dTb = Akbar•m(solute)•i

43
Q

Osmotic pressure (pi)

A 
pi = CRT
C = concentration of the solution
T = temp in kelvin

Chemistry GRE (29 decks)

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