What is the standard free energy change, ∆ G °, for a reaction? What is the standard free energy of formation, Δ G f ∘ for a substance? How are Δ G f ∘ values used to calculate Δ G rxn ∘ ? How can you use Hess’s law to calculate Δ G rxn ∘ ? How can you use ∆H ° and ∆ S ° values to calculate Δ G rxn ∘ ? Of the functions ∆ H°, ∆ S °, and ∆ G °, which depends most strongly on temperature? When ∆ G ° is calculated at temperatures other than 25°C,what assumptions are generally made concerning ∆ H° and ∆ S °?
What is the standard free energy change, ∆ G °, for a reaction? What is the standard free energy of formation, Δ G f ∘ for a substance? How are Δ G f ∘ values used to calculate Δ G rxn ∘ ? How can you use Hess’s law to calculate Δ G rxn ∘ ? How can you use ∆H ° and ∆ S ° values to calculate Δ G rxn ∘ ? Of the functions ∆ H°, ∆ S °, and ∆ G °, which depends most strongly on temperature? When ∆ G ° is calculated at temperatures other than 25°C,what assumptions are generally made concerning ∆ H° and ∆ S °?
Solution Summary: The author explains that thermodynamics is associated with heat, temperature, and its relation with energy and work. It helps us to predict whether a process will take place or not.
What is the standard free energy change, ∆G°, for a reaction? What is the standard free energy of formation,
Δ
G
f
∘
for a substance? How are
Δ
G
f
∘
values used to calculate
Δ
G
rxn
∘
? How can you use Hess’s law to calculate
Δ
G
rxn
∘
? How can you use ∆H° and ∆S° values to calculate
Δ
G
rxn
∘
? Of the functions ∆H°, ∆S°, and ∆G°, which depends most strongly on temperature? When ∆G° is calculated at temperatures other than 25°C,what assumptions are generally made concerning ∆H° and ∆S°?
Q2. Consider the hydrogenation of ethylene
C2H4 + H2 = C2H6
The heats of combustion and molar entropies for the three gases at 298 K are given by:
C2H4
C2H6
H2
AH comb/kJ mol¹
-1395
-1550
-243
Sº / J K¹ mol-1
220.7
230.4
131.1
The average heat capacity change, ACP, for the reaction over the temperature range 298-1000 K is
10.9 J K¹ mol¹. Using these data, determine:
(a) the standard enthalpy change at 800 K
(b) the standard entropy change at 800 K
(c) the equilibrium constant at 800 K.
13. (11pts total) Consider the arrows pointing at three different carbon-carbon bonds in the
molecule depicted below.
Bond B
Bond A
Bond C
a. (2pts) Which bond between A-C is weakest? Which is strongest? Place answers in
appropriate boxes.
Weakest
Bond
Strongest
Bond
b. (4pts) Consider the relative stability of all cleavage products that form when bonds A,
B, AND C are homolytically cleaved/broken. Hint: cleavage products of bonds A, B,
and C are all carbon radicals.
i. Which ONE cleavage product is the most stable? A condensed or bond line
representation is fine.
ii. Which ONE cleavage product is the least stable? A condensed or bond line
representation is fine.
c. (5pts) Use principles discussed in lecture, supported by relevant structures, to
succinctly explain the why your part b (i) radical is more stable than your part b(ii)
radical. Written explanation can be no more than one-two succinct sentence(s)!
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Statifically more chances to abstract one of these 6H
11. (10pts total) Consider the radical chlorination of 1,3-diethylcyclohexane depicted below. 4
4th total
• 6H total
래
• 4H total
21 total
ZH
2H
Statistical
H < 3° C-H weakest
-
product
abstraction here
bund
leads to thermo favored
a) (6pts) How many unique mono-chlorinated products can be formed and what are the
structures for the thermodynamically and statistically favored products?
Product
6
Number of Unique
Mono-Chlorinated Products
Thermodynamically
Favored Product
Statistically
Favored Product
b) (4pts) Draw the arrow pushing mechanism for the FIRST propagation step (p-1) for the
formation of the thermodynamically favored product. Only draw the p-1 step. You do
not need to include lone pairs of electrons. No enthalpy calculation necessary
H
H-Cl
Waterfox
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