1. Decide whether the following are true or false. If it is false, revise the unbolded part of the sentence to make it true.
a) Plastics will decrease in quality when recycled because nature tends to move T F
towards disorder.
b) A spontaneous process is one that will start by itself but require constant T F
intervention thereafter.
c) A microstate is a manner in which a collection of particles attain a T F
particular energy. The number of microstates increases upon cooling of
the system, which increases the entropy of the system. Explain.
d) The reaction 2SO3(g) 2 SO2(g) + O2(g) will result in an increase T F
in entropy.
e) The third law of thermodynamics states that the entropy of a perfect crystal is T F
100 at 0 K.
f) The net result of the Chapman Cycle is 0. T F
g) As a reaction progresses, the rate of reaction increases. T F
h) The collision between two molecules will result in a chemical reaction T F
when the molecules have enough energy and are positioned correctly with
respect to each other.
i) The double sided arrow on the following graph represents ∆E. T F
Energy
Reaction Progress
j) The turnover number is the number of molecules that can react per catalyst T F
binding site per unit time.
2. In a certain spontaneous process the system undergoes an entropy change, ∆S = -36 J/K. What
can you conclude about ∆Ssurr? (2nd law of thermodynamics)
3. Which of the following is/are a spontaneous process? Circle all that apply.
a) Spreading of the fragrance of perfume through a room.
b) Separating a mixture of N2 and O2 into two separate samples, one that is pure N2 and one
that is pure O2.
c) The bursting of an inflated balloon.
d) The reaction of sodium metal with chlorine gas to form sodium chloride.
4. Calculate ∆H and ∆S for the following reaction. Using those values, calculate ∆G. Is it
spontaneous? If it is, is it entropy or enthalpy driven or both?
SO2(g) + 2H2(g) S (s) + 2H2O(g)
5. The element cesium (Cs) freezes at 28.4⁰C and its molar enthalpy of fusion is ∆Hfus= 2.09
kJ/mol. Calculate the value of ∆S (in J/K) when 15.0 g of Cs(l) solidifies at 28.4⁰C.
6. Consider the combustion of ethylene, C2H4(g) + 3 O2(g) 2 CO2(g) + 2 H2O(g). If the concentration of C2H4 is decreasing at a rate of 0.55 M/s (mol x L-1 x s-1), what is the rate of formation of CO2?
7. The following data were measured for the reaction BF3(g) + NH3(g) F3BNH3(g):
[BF3], M / [NH3], M / Rate, M/s0.250 / 0.250 / 0.2130
0.250 / 0.125 / 0.1065
0.200 / 0.100 / 0.0682
0.350 / 0.100 / 0.1193
0.175 / 0.100 / 0.0596
a) Write the rate law for this reaction.
b) Calculate the rate law constant.
c) What is the rate when [BF3] = 0.100 M and [NH3] = 0.500 M?
8. The gas-phase decomposition of NO2, NO2(g) NO(g) + O2(g), is studied at 383⁰C, giving
the following data:
Time (s) / [NO2] (M)0.0 / 0.100
5.0 / 0.017
10.0 / 0.0090
15.0 / 0.0062
20.0 / 0.0047
a) Is the reaction first order or second order with respect to concentration of NO2?
b) What is the value of the rate constant?
9. The first-order rate constant for the decomposition of N2O5, N2O5(g) 2 NO2(g) + O2(g), at
70⁰C is 6.82 x 10-3s-1. What is the half-life of N2O5?
10. A certain first-order reaction has a rate constant of 2.75 x 10-2 s-1 at 20⁰C. What is the value
of k at 80⁰C if Ea = 75.5 kJ/mol? (R= 8.314 J/mol-K)
11. The following mechanism is proposed for a reaction:
NO + Br2 NOBr2
NOBr2 + NO 2 NOBr
a) Write the balanced equation for the overall reaction.
b) Identify any intermediates in the mechanism.
c) What molecularity is the overall reaction?
12. Gaseous hydrogen iodide is placed in a closed container at 425⁰C, where it partially
decomposes to hydrogen and iodine: 2HI(g) H2(g) + I2(g). At equilibrium it is found
that [HI] = 3.53 x 10-3 M, [H2] = 4.79 x 10-4 M, and [I2] = 4.79 x 10-4 M. What is the value of
K at this temperature?
Know how to do #11.57 in your text book! I don’t think we’ll have time for an example.