Thermodynamics Review Sheet 1
1. Those reactions that involve “energy spread” tend to occur in nature (i.e. be
spontaneous). How does this energy spread relate to the ∆H of a reaction?
2. Those reactions that involve “matter spread” tend to occur in nature (i.e. be spontaneous).
How does this matter spread relate to the ∆S of a reaction?
3. For the following processes, indicate whether the process involves a net increase or
decrease in energy spread and the sign of ∆H, and whether the process involves a net
increase or decrease in matter spread and the sign of ∆S.
a) Evaporation of a liquid
energy spread increase or decrease
∆H = _____
fav or unfav
matter spread increase or decrease
∆S = _____
fav or unfav
b) Freezing of a liquid
energy spread increase or decrease
∆H = _____
fav or unfav
matter spread increase or decrease
∆S = _____
fav or unfav
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c) Adding energy to decompose a compound to its elements
energy spread increase or decrease
∆H = _____
fav or unfav
matter spread increase or decrease
∆S = _____
fav or unfav
4. Iindicate what each term in the Gibbs free energy equation represents:
∆G represents the “net driving force” of the reaction
∆H represents
T represents
∆S represents
5. The table below shows all possible combinations of signs for the enthalpy changes (∆H)
and entropy changes (∆S) in any process. Enter a +, or -, or T in the ∆G column to
correspond to these changes. Use T for temperature if the sign of ∆G dependson the
temperature. If the sign of ∆G depends on the temperature, specify whether the reaction
is spontaneous at a high or low temperature.
∆S
∆H
+
-
-
+
+
+
-
-
∆G + or∆G –
or T dependent
Spontaneous?
Enter yes or no or specify if it is
Spontaneous at a high T or a low T
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6. Given the reaction:
H2(g) + CO2(g)  H2O(g) + CO(g)
∆H = 41.8 kJ
∆S = 42.2 J/K
a) Is the reaction endothermic or exothermic? Explain.
b) Does this involve an increase or decrease in energy spread?
c) Is there a net increase or decrease in entropy? Explain.
d) Does this involve an increase or decrease in matter spread?
e) Calculate the Gibbs free energy change (∆G) for this reaction at 25oC and predict
whether the reaction occurs spontaneously at room temperature (25oC).
f) What will be the value of ∆G when the reaction comes to an equilibrium (equilibrium
occurs when the rates of the forward and reverse reactions become equal).
g) Determine the Celsius temperature at which equilibrium will occur.
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h) Draw a rough PE diagram and label the axis, indicate the interval representing ∆H
and the activation energy (Ea)
7. The Haber process for the production of ammonia gas (NH3) involves the reaction of
elemental hydrogen and nitrogen gases to produce ammonia.
a) Write a balanced chemical equation to represent this reaction. Balance the equation
by adjusting coefficients.
b) Given the following thermodynamic data:
∆Hf for NH3(g) = -46 kJ/mol
S for N2(g) = 192 J/K
S for H2(g) = 131J/K
S for NH3(g) = 193 J/K
Calculate ∆H for the reaction and indicate whether it is exothermic or endothermic.
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c) Does the ∆H term involve increasing energy spread or decreasing energy spread?
d) Predict the sign of ∆S for the reaction.
e) Does the ∆S term involve increasing matter spread or decreasing matter spread?
f) Calculate the ∆S for the reaction.
g) Does your calculation in (f) match your prediction in (d)?
h) Calculate the ∆G for the reaction at 25oC.
i) Is the reaction spontaneous at room temperature? How do you know?
j) Can you determine the temperature at which this reaction may become spontaneous
(hint: this is the equilibrium temperature).
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8. Write a balanced equation for the decomposition of solid copper(II)carbonate to solid
copper(II)oxide and carbon dioxide gas by the addition of heat and discuss the
spontaneity of the reaction using thermodynamic principles.
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