Chapter 8, Chemical and Physical Change
1.
Complete in not more than ten words: Thermodynamics deals with
………………
Ans.
2.
energy changes in chemical reactions.
Name, in order, the three thermodynamic quantities represented by H, S
and G (as in ∆H°, ∆S° and ∆G°).
Ans.
3.
enthalpy, entropy, free energy
Explain what is meant by "system" and "surroundings" in thermodynamics.
Ans.
The system is the reaction or process being studied; the surroundings
are the remainder of the universe.
What is another name for the first law of thermodynamics?
4.
Ans.
5.
law of conservation of energy
Circle the appropriate word in each of the underlined pairs:
In an endothermic reaction, the products are initially formed
hotter/colder than the reactants, and in returning to the temperature
of the surroundings, the system gains/loses heat from/to the
surroundings.
Ans.
6.
colder; gains
What is the name and symbol of the thermodynamic quantity (function)
which is equal to the heat absorbed or liberated in a chemical reaction
at constant pressure?
Ans.
7.
enthalpy change, ∆H°
Circle the appropriate word in each of the underlined pairs:
A reaction will never be spontaneous if it is exothermic/endothermic
and there is an/a increase/decrease in disorder of the system.
Ans.
8.
endothermic; decrease
What is the name and symbol of the single thermodynamic quantity
(function) which determines whether or not a reaction is spontaneous?
Ans.
9.
free energy change, ∆G°
What is the name of the technique for measuring the heat energy
absorbed or released in a chemical reaction?
Ans.
10.
calorimetry
How many small calories are equivalent to one nutritional Calorie?
Ans.
11.
1000 cal
Fill in the blanks: The specific heat of a substance is the number of
_______ needed to raise the temperature of _______ of the substance by
_______.
Ans.
12.
calories (or joules); one gram; 1°C
What process is the main source of energy in the human body?
Ans.
combustion of carbohydrates
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Chapter 8, Chemical and Physical Change
13.
A candy sample is completely combusted in a bomb calorimeter. The
calorimeter contains 982 g of water, and the measured temperature
increase is 2.62°C. What is the fuel value of the candy sample in
nutritional Calories?
Ans.
14.
2.57 Calories
A carbohydrate sample weighing 0.235 g was found to have a fuel value
of 3.84 kJ. What is the fuel value of one gram of this carbohydrate, in
nutritional Calories?
Ans.
15.
3.91 Calories
Complete in not more than ten words: Kinetics deals with …………………
Ans.
16.
the rates (and mechanisms) of chemical reactions.
What is the term used for the height of the energy barrier the
reactants must overcome in order to form products in a reaction?
Ans.
17.
activation energy
Complete the following potential energy diagram for a reaction, in
order to clearly identify the activation energy, the activated complex
and the energy absorbed or released in the reaction.
reactants
products
Progress of reaction
Ans.
activated complex
activation energy
reactants
energy released
products
Progress of reaction
18.
Ans.
19.
In one sentence, define a catalyst.
It is a substance which speeds up a chemical reaction without being
consumed in the process.
What is the name given to a biological catalyst?
Ans.
20.
enzyme
A reaction is first order in reactant A, first order in B and second
order in C. Write down the rate equation for this reaction.
Ans.
rate = k[A][B][C]2
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Chapter 8, Chemical and Physical Change
21.
Ans.
22.
For any given reaction, list three different ways in which one might
speed up the reaction rate.
increase concentrations of reactants; increase temperature; add a
catalyst
Write the equilibrium constant expression for the reaction:
2NO(g)
+
K eq =
NO 2
Ans.
23.
O 2(g)
2NO 2(g)
2
NO 2 O 2
Write the equilibrium constant for the following reaction (think
carefully!):
MgCO 3(s)
Ans.
24.
MgO(s)
+
CO 2(g)
Keq = [CO2]
In the industrial synthesis of ammonia, the equilibrium constant
expression may be written as
K eq =
NH 3
N2
2
H2
3
Calculate the value of this equilibrium constant, if the equilibrium
concentrations in the reaction mixture at 600°C are:
[N2] = 0.830 M; [H2] = 2.49 M; [NH3] = 7.62 M
Ans.
25.
4.53
State LeChatelier's principle.
Ans.
If a stress is applied to a system at equilibrium, the equilibrium will
shift in such a way as to minimize that stress.
When a cold-pack is activated, a chemical reaction occurs and the
temperature of the pack contents drops sharply. Which of the following
is a correct description of the reaction occurring in the pack?
26.
A.
B.
C.
D.
E.
Ans.
27.
C
What is the measure of the randomness or disorder of a chemical system?
A.
B.
C.
D.
E.
Ans.
The reaction is exothermic; ∆H° > 0
The reaction is exothermic; ∆H° < 0
The reaction is endothermic; ∆H° > 0
The reaction is endothermic; ∆H° < 0
None of the above statements is correct.
energy
calorimetry
entropy
enthalpy
free energy
C
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Chapter 8, Chemical and Physical Change
28.
In general, which state of matter has the lowest entropy?
A.
B.
C.
D.
E.
Ans.
29.
A
Under normal conditions, which of the following would have the highest
entropy?
A.
B.
C.
D.
E.
Ans.
30.
1000 cal
100.0 cal
6.50 cal
1250 cal
650 cal
E
Ethylene glycol has a specific heat of 0.578 cal/(g°C). If 23.2 g of
ethylene glycol absorbs 75.6 cal of heat energy, what will the
temperature increase be?
A.
B.
C.
D.
E.
Ans.
7.74 × 10-1 kJ
4.42 × 10-2 kJ
442 kJ
774 kJ
1.85 105 kJ
D
When a sample of aqueous hydrochloric acid was neutralized with aqueous
sodium hydroxide in a calorimeter, the temperature of 100.0 g of water
surrounding the reaction increased from 25.0°C to 31.5°C. If the
specific heat of water is 1.00 cal/(g°C), calculate the quantity of
energy in calories involved in this neutralization reaction.
A.
B.
C.
D.
E.
Ans.
32.
oxygen gas
liquid water
ice
solid sodium chloride
solid iron
A
A granola bar contains 185 nutritional Calories. How many kilojoules is
this?
A.
B.
C.
D.
E.
Ans.
31.
solid
liquid
gas
plasma
supercritical fluid
0.177°C
1.88C
5.64C
1.01 × 103°C
3.03 × 103°C
C
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Chapter 8, Chemical and Physical Change
33.
In the potential energy diagram for a chemical reaction, what is the
name used for the unstable species corresponding to the top of the
energy barrier separating reactants from products?
A.
B.
C.
D.
E.
Ans.
34.
B
Which one of the following actions can alter the activation energy of a
reaction?
A.
B.
C.
D.
E.
Ans.
35.
to increase the rate of collisions between reactants
to slow down the rate of the reverse reaction
to raise the temperature of the mixture
to provide a new pathway for the reaction
none of the above
is the inverse of the entropy of the system
is measured experimentally
can be deduced from the balanced equation for the reaction
depends on the rate constant
depends on the concentrations of reactants
B
When a chemical reaction reaches equilibrium
A.
B.
C.
D.
E.
Ans.
the temperature
the concentration of reactants
the concentration of products
the size of the reaction vessel
catalyst
D
In kinetics, the order of a reaction
A.
B.
C.
D.
E.
Ans.
37.
changing
changing
changing
changing
adding a
E
One effect of a catalyst being added to a reaction mixture is
A.
B.
C.
D.
E.
Ans.
36.
catalyst
activated complex
intermediate
free radical
substrate
the
the
one
the
the
forward reaction stops
reverse reaction stops
of the reactants has been completely consumed
equilibrium constant has reached its maximum value
rates of the forward and reverse reactions are equal
E
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Chapter 8, Chemical and Physical Change
38.
Consider the reversible reaction:
A(g)
2B(g)
At equilibrium, the concentration of A is 0.381 M and that of B is
0.154 M. What is the value of the equilibrium constant, Keq?
A.
B.
C.
D.
E.
Ans.
39.
0.0622
0.404
1.06
2.47
16.1
A
Consider the reversible reaction:
N 2(g) + 3H2(g)
2NH 3(g)
What is the correct expression for the equilibrium constant, Keq, for
this reaction?
A.
Ans.
40.
B.
2[ NH 3 ]
[ N 2 ]3[H 2 ]
[ N 2 ][ H 2 ]
3
[ N 2 ][ H 2 ] 3
[ NH 3 ]
2
E.
[ N 2 ]3[ H 2 ]
2[ NH 3 ]
C
The reaction below is at equilibrium. Use LeChatelier's principle to
predict the effect of adding more hydrogen gas to the equilibrium
reaction mixture.
A.
B.
C.
D.
E.
43.
D.
[ NH 3 ] 2
concentration of reactants
concentration of the products
temperature
catalyst
size of reaction vessel
N2(g) + 3H 2(g)
Ans.
42.
C.
C
Which one of the following, if changed, would change the value of
equilibrium constant, Keq, of a reaction?
A.
B.
C.
D.
E.
Ans.
41.
[2NH 3 ]
[ N 2 ][3H 2 ]
B
T
The
The
The
The
All
F
2NH 3(g)
equilibrium position will remain unchanged.
equilibrium position will shift to the right.
equilibrium position will shift to the left.
equilibrium constant will increase.
of the nitrogen gas will be used up.
The driving force of a chemical reaction is to attain a state of
higher potential energy.
Ans.
T F
F
Exothermic reactions are often, but not always, spontaneous.
Ans.
T
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Chapter 8, Chemical and Physical Change
44.
T
F
45.
Ans.
T F
F
A reaction that leads to an in increase in the entropy of the
system is always spontaneous.
46.
Ans.
T F
F
A reaction that leads to a decrease in the enthalpy of the system
is always spontaneous.
47.
Ans.
T F
F
A reaction that leads to a decrease in the free energy of the
system is always spontaneous.
48.
Ans.
T F
T
According to the second law of thermodynamics, a system and its
surroundings spontaneously tend towards increasing order.
49.
Ans.
T F
F
In general, a liquid state will have a higher entropy than a
solid state.
50.
Ans.
T F
T
A collision between reactant molecules which produces one or more
product molecules is called an effective collision.
51.
Ans.
T F
T
Lowering the activation energy of a reaction will decrease its
rate.
52.
Ans.
T F
F
The order of a reaction with respect to any reactant is shown in
the rate equation.
53.
Ans.
T F
T
The equilibrium constant expression for a reaction can be written
down if the balanced equation is known.
54.
Ans.
T F
T
Reactants and products which are solids or pure liquids do not
appear in the equilibrium constant expression.
55.
Ans.
T F
T
Changing the temperature alters the value of the equilibrium
constant for a reaction.
56.
Ans.
T F
T
LeChatelier's principle provides information about the rate of a
reaction.
Ans.
F
Endothermic reactions are never spontaneous.
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Chapter 8, Chemical and Physical Change
57.
T
F
58.
Ans.
T F
T
A catalyst increases the equilibrium constant for a reaction.
Ans.
F
Removal of a gaseous product from an equilibrium reaction mixture
shifts the equilibrium toward formation of more products.
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