Ch 19 Lesson Plan - FA2020 PDF

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CHM 115 ▪

Lesson Plan

Chapter 19 (1 of 2)

The first law of thermodynamics (Recall CHM 113): ▪ total _________ of an isolated system is ___________; ▪ energy can be transformed from one form to another, but cannot be _________ or _________. ▪ _________ of the universe is _________

Thermodynamics – the study of ____________, ____________, and ____________. ▪ ▪ ▪

applied to _________ change ▪ e.g., calculate the quantity of heat obtained from combustions of one gallon of fuel oil applied to _________ change ▪ e.g., Determine the energy released by boiling water The Laws of Thermodynamics: ▪ Tells us whether a process (chemical or __________) process will occur ▪ _____________ (i.e., ___________ outside intervention) or ▪ _____________ (i.e., ___________ outside intervention). ▪ Does not tell us about the __________ of the process

How to measure SPONTANEOUS and NONSPONTANEOUS reactions Change in Free Energy (_____) ΔG < O product-favored process: _________________ ΔG > O reactant-favored process: _________________ **ΔG = O __________________

G =  nG  f (products ) −  m G  f (reactants )

ΔG = ΔH – TΔS ΔH: change in __________ T: Temperature (_) ΔS: change in __________

For the reaction C(s) + O2 (g) ----> CO 2 (g)

ΔH° = -394 kJ / mol;

.

ΔS° = 42.9 J / (mole K) a. What is ΔG° (kJ /mol) at 25 °C? b. What is ΔG when 0.32 mol of C reacts?

Calculating ΔH: (Recall CHM113) ▪ Hess’s Law ▪ H  = n H  f (products ) −



ΔG = ΔH – TΔS ΔH: change in __________ T: Temperature (_) ΔS: change in __________

 m H  (reactants ) f

Most, but not all, ___________ reactions are spontaneous, depends on _________________

Calculating ΔS:

S  =  n S  (products ) −  m S  (reactants ) The 2nd law of thermodynamics – the universe spontaneously tends toward _____________ disorder or randomness Third Law of Thermodynamics: The entropy of a perfect crystal at 0 K is _______ The entropy of a substance _____________ with temperature Entropy (S°) Units _____________: - measure of the _______________ or disorder - describes the number of _______________ that are available to a system existing in a given ________. - Nature spontaneously proceeds toward the states that have the __________ probabilities of __________. - An ____________ in entropy gives a driving force for a ____________ process - A __________ ∆So means an __________ in __________ for the reaction - A __________ ∆So means a __________ in __________ for the reaction Positional Entropy ▪ States with increasing disorder (Ssolid

Sliquid

Qualitative Guidelines for ∆S 1. 2. 3. 4. 5.

# of molecules (gases) (total) Phase Changes: Gas >>> Liquids > Solids Dissolving Higher temperature Molecular Size (within same state of matter)

Entropy Changes in the System (∆Ssys)

Sgas)

When gases are produced (or consumed) • • •

If a reaction produces more gas molecules than it consumes, ∆S0 > 0. Entropy ____________ If the total number of gas molecules diminishes, ∆S0 < 0. Entropy ____________ If there is no net change in the total number of gas molecules, then ∆S0 may be positive or negative BUT ∆S0 will be a small number.

Q. What is the sign of the entropy change for the following reaction? 2Zn (s) + O2 (g) → 2ZnO (s) The total number of gas molecules goes down, ∆S is ___________ Predict the sign (+ or -) of ΔS for each of the following, and explain: a) The evaporation of alcohol _____ b) The freezing of water _____ c) Compressing an ideal gas at constant temperature _____ d) Heating an ideal gas at constant pressure _____ e) Dissolving NaCl in water _____

a) _____ (a liquid is turning into a gas) b) _____ (more order in a solid than a liquid) c) _____ (the volume of the container is decreasing) d) _____ (the volume of the container is increasing) e) _____ (there is less order as the salt dissociates and spreads throughout the water) ▪

Which substance has the greatest entropy? ▪ or Na(s) ▪ H2O(l) or

Q3. Find ΔS° for: CaCO3 (s) → CaO (s) + CO2 (g) S° CaCO3 (s) = 93 J / (mole . K); S° CaO (s) = 38 J / (mole . K); S° CO2 (g) = 213 J / (mole .K)

Effect of ΔH and ΔS on Spontaneity

o

o

If exothermic (H = -) and s = +) o

________________

o

If endothermic (H = +) and s = -)

________________

For any other situations, it depends on the relative size of ΔHo and ΔSo

If H = (______) and S = (______), then G = (-) only at ___________ temperature If H = (______) and S = (______), then G = (-) only at ___________ temperature

Q6. Under which temperature conditions will the following reaction be spontaneous? C (s) + H2O (g) → CO (g) + H2 (g) ΔH°= +131 kJ/mol ΔS° = +134 J/mol•K a. Above 273°C

b. Above 325°C

c. Above 552°C

d. Above 705°C

e. At all temperatures

CHM 115

Lesson Plan

Chapter 19 (2 of 2)

Free Energy and Chemical reactions, Pressure, Equilibrium

G =  nG  f (products ) −  m G  f (reactants ) ΔG° (Standard free energy of reaction) is the free energy change for a reaction when it occurs under standard-state conditions, when reactants in their standard states are converted to products in their standard states _______ (Standard free energy of formation) is the free-energy change that occurs when _______ of the compound is formed from its elements in their standard states. ΔG = free energy under nonstandard state conditions ΔG = ΔG° + RT ln(Q) R is the gas constant (8.314 J/K•mol); T is absolute temperature (K) Q is the reaction quotient At Equilibrium Q = K, ΔG = 0 ΔG° = -RT ln (K)

The equilibrium constant (K) for the reaction N2O4 (g) → 2NO2 (g) is 0.113 at 298 K, where the ΔG° = 5.4 kJ/mol. (a) In a certain experiment, the initial concentrations are - [NO2] = 0.112 M - [N2O4] = 0.453 M (i) Calculate ΔG for the reaction at these pressure (ii) Predict direction of the net reaction towards equilibrium

(b) In a certain experiment, the initial concentrations are - [NO2] = 0.453 M - [N2O4] = 0.112 M (i) Calculate ΔG for the reaction at these pressure (ii) Predict direction of the net reaction towards equilibrium

A reaction is _________________(ΔG = ___) in the direction the equilibrium will shift, as per the Q vs K. Enthalpy change (ΔH) is the measure of dispersion or randomness of ____________________. Entropy change (ΔS) is the measure of dispersion or randomness of ____________________. Qualitative assessment (without calculation) ΔH ΔS ΔG

Quantitative assessment (requires calculation...