Energy And Enthalpy Worksheet With Answers Page 5
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1
2
3
4
5(d) What is the entropy change of the water bath?
-1
ΔS
= ΔH
/ T = 1801.9 J/ 273K = 6.6 J K
H2O
H2O
(e) What is the total entropy change?
-1
-1
-1
ΔS
= ΔS
+ ΔS
= -4.95 J K
+ 6.6 J K
= 1.65 J K
tot
Al
H2O
15. The following reaction is performed at a constant temperature of 298 K and a
-1
pressure of 1 atm. Given that ΔH°
(NH
)(g) = -46.11 kJ mol
and ΔG°
(NH
)(g) = -
f
3
f
3
-1
16.48 kJ mol
.
(g) ➝ 2NH
N
(g) + 3H
(g)
2
2
3
If the reaction moves from reactants to products what sign would you expect for each of
the following:
q
Positive
Negative
Zero
No Way to Know
w
Positive
Negative
Zero
No Way to Know
ΔH (system) Positive
Negative
Zero
No Way to Know
ΔS (system)
Positive
Negative
Zero
No Way to Know
Comparing the energy and the enthalpy you would expect which of the following
describes this reaction:
ΔH > ΔU
ΔH < ΔU
ΔH = ΔU
Do you expect the reaction to be “spontaneous”?
Yes
No
If “Yes” or “No” is there a temperature at which it will be non-
spontaneous/spontaneous?
Yes
ΔG = ΔH - T ΔS
-1
-1
-
ΔS = (ΔG – ΔH) / -T = ((-16.48 kJ mol
) – (-46.11 kJ mol
)) / -298 K = -0.0994 kJ K
1
-1
mol
-1
-1
-1
T = ΔH / ΔS = -46.11 kJ mol
/ -0.0994 kJ K
mol
= 463.9 K
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