EXERCISES
1. Consider the reaction, 2HI → H2 + I2, determine the rate of disappearance of HI when the rate of I2
formation is 1.8 x 10-6 Ms-1.
Answer : 3.6 × 10-6 Ms-1
2. Because it has a nonpolluting product (water vapor), hydrogen gas is used for fuel aboard the
space shuttle and may be used by Earth-bound engines in the near future.
2H2(g) + O2(g) 2H2O(g)
• Express the rate in terms of changes in [H2],
[O2] and [H2O] with time.
• When [O2] is decreasing at 0.23 molL-1 s-1, at
what rate is [H2O] increasing?
Answer : 0.46molL-1s-1
3. Consider the reaction,
NO(g) + O2(g) →2NO2(g).
Suppose that at a particular moment during the
reaction nitric oxide (NO) is reacting at the rate
of 0.066 Ms-1
a) At what rate is NO2 being formed?
b) At what rate is molecular oxygen reacting?
4. Consider the reaction,
N2(g) + 3H2(g) → 2NH3(g)
Suppose that at a particular moment during the reaction molecular hydrogen is reacting at the
rate of 0.074 Ms-1
a) At what rate is ammonia being formed?
b) At what rate is molecular nitrogen reacting?
5. ClO2(aq) + 2OH- (aq) → products
The results of the kinetic studies are given below.
exp [ClO2] / M [OH-] / M Initial rate / Ms-1
1 0.0421 0.0185 8.21 ×10-3
2 0.0522 0.0185 1.26 ×10-2
3 0.0421 0.0285 1.26 ×10-2
a) Explain what is meant by the order of reaction
b) Referring to the data determine
(i) rate law /rate equation
(ii) rate constant, k
(iii) the reaction rate if the concentration of both ClO2 and OH- = 0.05 M
Answer : rate = k [ClO2]2[OH-]
k = 250 M-2s-1
rate = 3.12 ×10-2 M/s
6. Write rate law for this equation,
A + B → C
i) When [A] is double, rate also double. But double the [B] has no effect on rate.
ii) When [A] is increase 3x, rate increases 3x, and increase of [B] 3x causes the rate to increase 9x.
iii) Reduce [A] by half has no effect on the rate, but reduce [B] by half causing the rate to be half of the
initial rate.
Answer : Rate = k[A]
Rate = k[A] [B]2
Rate = k[B]
7. C + D → E
The results of the kinetic studies are given below.
Answer : a) 8.33 ×10-5 ,3.33 × 10-4, 4.17×10-5 M min-1
b) rate = k [C] [D]2 c) rate increase by a factor of 4
8. The reaction 2A to B is first order in A with a rate constant of 2.8 x 10-2 s-1 at 800oC.M to 0.14 M ?
Answer : a)
b) [H2O2] = 0.387 M
10. The decomposition of ethane, C2H6 to methyl radicals is a 1st order reaction with a rate constant-4 s-1 at 700o C.2H6(g) to 2CH3(g)
Calculate the half life of the reaction in minutes.
Answer : t1/2 = 2 1 . 5 min
11. The decomposition of nitrogen pentoxide is as below;
N
time, t/min 0 10 20 30 40 50 60 [N2O5] x 10-4 M 176 124 93 71 53 39 29
Answer : k = 0.0296 s-1
12. The decomposition of HI is second order, at 500oC, the halflife of HI is 2.11 min when the initial HI concentration is 0.10 M. What will be the half-life (in minutes) when the initial HI concentration is 0.010 M?
Answer : 21 minutes
13. The rate constant for the first-order decomposition of N2O5(g) at 100oC is 1.46 x10-1s-1.
a) If the initial concentration of N2O5 in a reaction vessel is 4.5 ×10-3 mol/L, what will the concentration
Answer : a) first
b) 102 kj per mola and A for the reaction. 10-5
Wednesday, 9 March 2011
Exercises
exp Initial [ ] (M) Time interval (Min) The change in concentration of C (M)
[C] [D]
1 0.10 1.0 30 2.5 x
10-3 2 0.10 2.0 30 1.0 x 10-2 3 0.05 1.0 120 5.0 x a) Calculate the rate of reaction for each experiment
b) Determine the order of reaction with respect to C and D and write the rate law.
How long will it take for A to decrease from 0.88
Answer : t = 66s
9. For the first order decomposition of H2O2(aq) given that k = 3.66 x 10-3 s-1 and [H2O2 ]o = 0.882 M,2 O2] = 0.600 M105.26 s
determine;
a) the time at which [H
b) the [H2O2] after 225 s. of 5.36 x 10
C
The decomposition is first order reaction.
a)Plot a linear graph to prove it.
b)From the plot determine rate constant, k be 20.0 s after the decomposition begins?
b) What is the half-life (in s) of N2O5 at 100oC?
Answer : a) 0.00024 M
b) 4.75 s
14. For the reaction A + B produce C + D, the enthalpy change of the forward reaction is + 21 kJ/mol. The activation energy of the forward reaction is 84 kJ/mol.
a) What is the activation energy of the reverse reaction ?
b) Sketch the reaction profile of this reaction.
15. In the presence of platinum as a catalyst, hydrogen iodide decomposes to form hydrogen and iodine. The activation energy for this reaction is 58 kJ mol-1. Calculate the ratio of the rate constant at 30oC and 20oC.
Answer : 0.46
16. The results of the decomposition of N2O5 at two different temperature were recorded as;10-5 308 6.61 x
a) Base on the unit of the rate constant, k, determine the order of the reaction.
b) Find the value of ETemperature(K) rate constant, k (s-1)
298 1.74 x
2O5(g) to 2 NO2(g) + ½ O2(g)10-3Posted by Reaction Kinetic at 12:34 0 comments
ha! jawab, jawab....(4.4)
1. | Phosgene, COCl2, one of the poison gases used during World War I, is formed from chlorine and carbon monoxide. The mechanism is thought to proceed by:
b. Identify any reaction intermediates. c. Identify any catalysts. | |||||||||||||||||||||||||||||||
a. The overall reaction:
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2. | We have typically been simplifying our potential energy curves somewhat; for multistep reactions, potential energy curves are more accurately shown with multiple peaks. Each peak represents the activated complex for an individual step. Consider the PE curve for a two-step reaction: | |||||||||||||||||||||||||||||||
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Posted by Reaction Kinetic at 07:08 0 comments
ha! jawab, jawab....(4.2&4.3)
1. | Consider the following reaction that occurs between hydrochloric acid, HCl, and zinc metal: HCl(aq) + Zn(s) → H2 (g) + ZnCl2 (aq) Will this reaction occur fastest using a 6 M solution of HCl or a 0.5 M solution of HCl? Explain. | ||||
Solution:The reaction will occur fastest with 6 M HCl, because it is more concentrated than the 0.5 M solution. In the more concentrated solution there are more moles of HCl present - with a higher concentration of reacting particles, collisions will occur more frequently, leading to a faster rate of reaction. | |||||
2. | Again consider the reaction between hydrochloric acid and zinc. How will increasing the temperature affect the rate of the reaction? Explain. | ||||
Solution:Increasing the temperature will most likely increase the rate of the reaction, for two reasons: | |||||
3. | Based on the following kinetic energy curves, which reaction will have a faster rate - A or B? Explain. Also, which reaction, A or B, would benefit most in terms of increased rate if the temperature of the system were increased? | ||||
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Solution:Reaction B would be faster than Reaction A because it has a lower threshold energy (activation energy). Thus, more particles have at least the minimum amount of energy required for a successful reaction. |
Posted by Reaction Kinetic at 07:07 0 comments
ha! jawab, jawab....(4.1)
1.
Which one of the following reactions would you expect to be fastest at room temperature and why?
Solution: | |
Pb2+(aq) + 2 Cl-(aq) →PbCl2 (s) | fastest - ions in aqueous solution react very quickly; all are in the same phase |
Pb(s) + Cl2 (g) → PbCl2 (s) | slower - one of the reactants is a solid |
2.
Consider the following reactions. Which do you predict will occur most rapidly at room conditions? Slowest?
Solution: | |
C2H6 (g) + O2 (g) → 2 CO2 (g) + 3 H2O(g) | slow due to covalent bonding (unless the reaction is highly exothermic) |
Fe(s) + O2 (g) → Fe2O3 (s) | slowest - solid reactant (Fe); this reaction describes the rusting of iron |
H2O(l) + CO2 (g) → H2CO3 (g) | slow due to covalent bonding |
2 Fe3+(aq) + Sn2+(aq) → 2 Fe2+(aq) + Sn4+(aq) | fastest - ions in solution react very quickly |
Posted by Reaction Kinetic at 07:04 0 comments
ha! jawab, jawab....(3)
1. | Answer the following questions based on the potential energy diagram shown here:
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Solution
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2. | Sketch a potential energy curve that is represented by the following values of ΔH and Ea. You may make up appropriate values for the y-axis (potential energy).ΔH = -100 kJ and Ea = 20 kJIs this an endothermic or exothermic reaction? | |||||||||
Solution: Since ΔH is a negative number, we know that the reaction is exothermic. Therefore, begin by sketching an exothermic potential energy graph: | ||||||||||
Next, assign values to the y-axis that will satisfy our requirements, namely ΔH = -20 kJ and Ea = +60kJRemember:
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3. | In the next unit we will be discussing reactions that are reversible, and can go in either the forward or reverse directions. For example, hydrogen gas and oxygen gas react to form water, but water can also be broken down into hydrogen and oxygen gas. We typically write a reaction that can be reversed this way, using the double arrow symbol ( or ↔):Consider a general reversible reaction such as:This reaction is exothermic in the forward direction:
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Given the following potential energy diagram for this reaction, determine ΔH and Ea for both the forward and reverse directions. Is the forward reaction endothermic or exothermic? | ||||||||||
Solution: You should immediately see that the forward reaction is exothermic - the products (C + D) are at a lower energy level than the reactants. |
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4. | Sketch a potential energy diagram for a general reaction A + B ↔ C + D Given that ΔHreverse = -10 kJ and Ea forward = +40 kJ | |||||||||
Solution:
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Posted by Reaction Kinetic at 07:02 0 comments
ha! jawab, jawab....(2)
1. | Nitrogen monoxide reacts with hydrogen gas to produce nitrogen gas and water vapour. The mechanism is believed to be:
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Solution To find the overall balanced equation, cross out substances that appear in equal numbers on both sides of the reaction and add together like items on the same side of the equation:
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2. | Give two reasons why most molecular collisions do not lead to a reaction. | ||||||||||
Solution: The collision may not have
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3. | An important function for managers is to determine the rate-determining steps in their business processes. In a certain fast-food restaurant, it takes 3 minutes to cook the food, 1.5 minutes to wrap the food, and 5 minutes to take the order and make change. How would a good manager assign the work to four employees? | ||||||||||
Solution: Assign two workers to take the orders since that is the rate determining step. |
Posted by Reaction Kinetic at 07:00 0 comments
ha! jawab, jawab....(1)
1. | In the following decomposition reaction, 2 N2O5 → 4 NO2 + O2 oxygen gas is produced at the average rate of 9.1 × 10-4 mol · L-1 · s-1. Over the same period, what is the average rate of the following:
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Solution:
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2. | Consider the following reaction: N2(g) + 3 H2(g) → 2 NH3(g) If the rate of loss of hydrogen gas is 0.03 mol · L-1· s-1, what is the rate of production of ammonia? | ||||||||
Solution: From the balanced equation we see that there are 2 moles NH3 produced for every 3 moles H2 used. Thus:
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Posted by Reaction Kinetic at 06:58 0 comments
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