Chapter 19 - Thermodynamics

Question 1

First law of Thermodynamics

Answer 1

Law of Conservation of Energy: The total energy of a closed system is constant (energy cannot be created or destroyed)
Secondly: the change of internal energy of a closed system is equal to the amount of heat supplied to the system + the work done on the system
(ΔE = q + w)

Question 2

Second Law of Thermodynamics

Answer 2

A process is spontaneous when it results in an overall increase in the entropy of system plus surroundings”

ΔSuniverse = ΔSsys + ΔSsurr > 0 (spont)
ΔSuniverse = ΔSsys + ΔSsurr = 0 (nonspont)

Nature favors disorder so Suni is not conserved; it is constantly increasing.

Question 3

Third Law of Thermodynamics

Answer 3

The entropy of a perfect pure crystal at 0K is zero.” There is no disorder. There is no movement.

Solid Liquid Gas
Order(s) > Order(l) &raquo_space; Order(g)
Entropy(s) < Entropy(l) &laquo_space; Entropy(g)

Entropy depends on the physical state of matter

Question 4

Microstates

Answer 4

N = # of microstates = n!/(e!(n-e)!)

Gas tends to spread out as much as it can

Question 5

Change of Entropy to the surroundings

Answer 5

ΔSsurr = -ΔHsys/T (only at constant T and P)
Entropy will have units of energy divided by temperature (J/K)

Question 6

Standard Entropy

Answer 6

Standard entropy is the entropy of one mole of a substance that is determined at the temperature of 298K (25oC) and 1atm.

Entropy is dependent on the amount of substance present
S°reaction = Σ nS°products – Σ nS°reactants (Like Enthalpy of Formation)

Question 7

Change of Entropy at phase changes

Answer 7

ΔSsys = ΔHsys / T (only at constant T and P)
Understand the general equation, solve by canceling units, assess if entropy is gained/lost

Question 8

Gibbs Free Energy

Answer 8

ΔG = ΔH – TΔS
For a change to be thermodynamically favorable, ΔG MUST BE NEGATIVE

Products - reactants is only for standard conditions

Question 9

Entropy

Answer 9

Entropy is dependent on temperature and the physical state of matter as well as the amount of matter present in the system, pressure of the system, and structure of matter (size)
Not only temperature, but direction of heat flow:
i.e. Exothermic rxns will increase entropy of surroundings because the resulting energy flow will increase the random motions of the surroundings

Question 10

After Equilibrium Equations

Answer 10

∆G = ∆G° + RTlnQ
∆G° = -RTlnK

R = 8.314 J/mol K

Question 11

Q vs K

Answer 11

Q = Product^n/Reactant^n

If Q > K, the reaction will shift to the reactants.
If Q < K, the reaction will shift to the products.
If Q = K, the reaction is at equilibrium