Thermodynamics 2

Question 1

The 2nd Law of Thermodynamics

Answer 1

The entropy of the universe tends to increase

S > 0

Question 2

Entropy

Answer 2

dS = dQ/T

Question 3

S total

Answer 3

S total = Ssystem + Ssurroundings

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

Question 4

The 3rd Law of Thermodynamics

Nernst heat theorem

Answer 4

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

Question 5

Entropy change at the transition

Answer 5

dS = dH/T

Question 6

Difference in entropy

Answer 6

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

Question 7

Calculate absolute entropy

Answer 7

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

Question 8

Debye Extrapolation

Answer 8

At low T, Cv = Cp = aT^3

Question 9

Joule’s Law

Answer 9

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

Question 10

Ideal gasses and solutions

Answer 10

dUt = 0
(dU/dV) = 0

Question 11

Joule’s Law

Answer 11

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

Question 12

Gay-Lussac’s law

Answer 12

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

Question 13

Gay-Lussac’s Law

Answer 13

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

Question 14

Boyle-Mariotte’s Law

Answer 14

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

Question 15

Endothermic thermochemistry

Answer 15

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

Question 16

Exothermic thermochemistry

Answer 16

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

Question 17

Hess’s Law

Answer 17

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

Question 18

Standard heat of formation

Answer 18

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

Question 19

Standard enthalpy of reaction

Answer 19

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

Question 20

Gives free energy

Answer 20

G = H - TS

Question 21

If dG < 0

Answer 21

Then the reaction is spontaneous

Question 22

If dG > 0

Answer 22

Then the reaction is not spontaneous

Question 23

If dG = 0

Answer 23

Then the system is in a state of equilibrium

Question 24

If dS > 0 & dH <0

Answer 24

Spontaneous at all temperatures

Question 25

If dS > 0 & dH > 0

Answer 25

Spontaneous at high temperatures

Question 26

If dS < 0 & dH < 0

Answer 26

Spontaneous at low temperatures

Question 27

If dS < 0 & dH > 0

Answer 27

Nonspontaneous at any temperatures

Question 28

Standard free energy

Answer 28

dGrx = sum of dGproducts - sum of dGreactants

Question 29

Chemical potential

Answer 29

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

Question 30

Gibb's phase rule

Answer 30

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

Question 31

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

Answer 31

The system is bivariant

Question 32

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

Answer 32

The system is univariant

Question 33

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

Answer 33

The system is invariant

Question 34

Bivariant

Answer 34

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

Question 35

Univariant

Answer 35

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

Question 36

Invariant

Answer 36

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

Question 37

Colligative properties

Answer 37

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

Question 38

Colligative properties

Answer 38

Freezing point depression, Boiling point elevation, Osmotic pressure

Question 39

Raoult's law

Answer 39

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

Question 40

Raoult's Law

Answer 40

``` 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 ```

Question 41

Freezing point depression dTf

Answer 41

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

Question 42

Boiling point elevation dTb

Answer 42

dTb = Akbar•m(solute)•i

Question 43

Osmotic pressure (pi)

Answer 43

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