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116 PLTL Activity sheet/ Colligative Properties
Set 2
Activity 1
You’re planning a fancy brunch and wish to make mimosa’s (a cocktail-like drink composed of chilled
champagne and orange juice.) Upon waking you remember that the champagne was not chilled.
Quickly you put several bottles of unopened champagne in your cooler that is just below zero-degrees
Celsius.
You are so frenzied that you remember the champagne three hours later. Should you be worried that
the champagne might be frozen? What would happen if you left a bottle of pure, filtered water in the
freezer at the same temperature? Explain.
Taken from Voyages in Conceptual Chemistry, Dan Barouch, Jones and Bartlett Publishers (1997).
Activity 2: Determine the greater quantity in each case
Substance A has a larger molar mass than substance B. You dissolve one gram of each in equal masses
of water. What solution has the higher vapor pressure? Assume both are non-electrolytes. Explain.
In the solutions made above, which solution has a higher boiling point? Which has a higher melting
point?
You have two solutions. One containing 1M table sugar and one contains 1M table salt. Which would
have a higher osmotic pressure?
You have two red blood cells. You dump one in pure water and dump the other in serum (the liquid
component of blood after the cells have been removed). In which would there be a higher osmotic
pressure difference?
Taken from Voyages in Conceptual Chemistry, Dan Barouch, Jones and Bartlett Publishers (1997).
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116 PLTL Activity sheet/ Colligative Properties
Set 2
Chemical Kinetics: Introductory Concepts
Chemical kinetics is the study of the rates of chemical reactions and the mechanisms by which
reactions occur. A rate is the change of a property (in this case, concentration) per unit time. The rate
of a chemical reaction is found by following the rate of disappearance (or decomposition) of one of
the reactants or the rate of appearance (or formation) of one of the products.
Suppose we consider the reaction N2(g) + 3 H2(g) → 2 NH3(g)
Since three H2 molecules react with one N2 molecule to produce two NH3 molecules, the rate of
disappearance of H2 will be three times the rate of disappearance of N2, and the rate of appearance of
NH3 will be twice the rate of disappearance of H2. Thus,
rate of
disappearance of
N2
 ∆[N2 ]
 − ∆t 
1
/3 the rate of
= disappearance of H2 =
1
/2 times the rate of
appearance of NH3
1  ∆[H 2 ] 
1  ∆[NH 3 ]
−


=
3
∆t
2  ∆t 
1
1
v H2
vNH 3
v N2
=
=
3
2
Note that rates are positive numbers (time doesn’t go backwards!).
=
In general, for the chemical equation
aA + bB → cC + dD
the rate is given by
1  ∆A  1  ∆B  1  ∆C  1  ∆D 
rate =  −
 = −
= 
= 

a  ∆t  b  ∆t  c  ∆t  d  ∆t 
rate = v =
1
1
1
1
vA = vB = v C = v D
a
b
c
d
Since the rates of appearance and disappearance of all reactants and products are related by the
equation stoichiometry, it doesn’t matter which rate we actually measure – experimental convenience
governs our choice. However, since the rates differ by stoichiometric ratios, we must specify the
substance for which our rate is defined
For the reaction P4 + 6 Cl2 → 4 PCl3, if the rate of disappearance of chlorine gas is 0.237 mole⋅L−1⋅s−1
What is the rate of the disappearance of phosphorus?
What is the rate of the appearance of phosphorus trichloride?
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116 PLTL Activity sheet/ Colligative Properties
Set 2
If we have the reaction A(g) → 2B(g) and the number of moles of A is as follows
Time, min
0
5
10
Moles A
0.100
0.085
0.070
What is the number of moles of B at 10 min?
a. 0.100 mole
b. 0.140 mole
c. 0.030 mole
d. 0.060 mole
e. 0.200 mole
What assumption was made in arriving at the correct answer?
For the reaction A → B + C the following data were obtained at 30C.
Exp
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2
3
[A], mole⋅L−1
0.170
0.340
0.680
Rate, mole⋅L−1 hr−1
0.0500
0.100
0.200
What is the rate equation, and what is the order of the reaction?
Calculate the rate constant for the reaction.
The equilibrium constant for the reaction is 0.500. Assume the reaction proceeds by a one-step
mechanism and calculate the rate constant for the reverse reaction.
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