Tutorial: Chemical Kinetics
1.
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The reaction of nitric oxide with hydrogen
at 1280 °C is
2NO (g)
+ 2H2 (g) ® N2
(g) + 2H2O (g)
From the
following data collected at this temperature, determine :
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(a)
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The rate law
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(b)
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The rate constant
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(c)
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The rate of the
reaction when [NO] = 12.0 x 10-3 M and [H2] = 6.0 x 10-3
M
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2.
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The
rate of the reaction between haemoglobin (Hb) and carbon monoxide (CO) was
studied at 20 °C. The
following data were collected with all concentration units in mmol/L. (A
haemoglobin concentration of 2.21 mmol/L is equal
to 2.21x 10-6 mol/L)
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(a)
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Determine
the orders of this reaction with respect to Hb and CO.
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(b)
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Determine
the rate law.
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(c)
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Calculate
the value of the rate constant.
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(d)
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What
would be the initial rate for an experiment with [Hb]0 = 3.36 mmol/L and [CO]0
= 2.40 mmol/L?
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3.
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The
graph represents the decomposition of of H2O2 at 45 °C.
2H2O2 (l)
® 2H2O (l) + O2 (g)
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(a)
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i.
Express the order of the reaction
ii.
Determine the initial concentration of H2O2.
iii.
Calculate the concentration of H2O2
after 10 hours.
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(b)
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Calculate
the initial rate of formation of H2O, given the rate constant is
1.0 x 10-3 min-1
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4.
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Write
the rate expressions for the following reactions in terms of the
disappearance of the reactants and the appearance of the products:
(i)
I- (aq) +
OCl- (aq) ® Cl- (aq) +
OI- (aq)
(ii)
4NH3 (g) +
5O2 (g) ® 4NO (g)
+ 6H2O (g)
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5.
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Consider
the reaction
4NO2 (g) +
O2 (g) ® 2N2O5 (g)
Suppose
that, at particular moment during the reaction, molecular oxygen is reacting
at the rate of 0.024 M/s.
(i)
At what rate is N2O5 being
formed?
(ii)
At what rate is NO2 reacting?
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6.
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Write
a balanced equation for a gas – phase reaction whose rate is given by:
Rate =
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7.
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® CH3 – CH = CH2
Cycloropane Propene
The
conversion of cyclopropane to propene in the gas phase is a first – order
reaction with a rate constant of s-1 at
500 °C.
(a)
If the initial concentration of cyclopropane was
0.25 M, what is the concentration after 8.8 min?
(b)
How long (in minutes) will it take for the
concentration of cyclopropane to decrease from 0.25 M to 0.15 M?
(c)
How long (in minutes) will it take to convert 74
percent of the starting material?
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8.
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The
reaction 2A ® B is first order in A with a rate
constant of s-1 at 80 °C. How long (in seconds) will it take
for A to decrease from 0.88 M to 0.14 M?
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9.
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A
certain first – order reaction is 35.5 percent complete in 4.90 min at 25 °C. what is its
rate constant?
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10.
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The
decomposition of ethane (C2H6) to methyl radicals is a
first – order reaction with a rate constant of at 700 °C:
C2H6(g)
® 2 CH3(g)
Calculate
the half – life of the reaction in minutes.
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11.
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Given
rate constant of the first – order decomposition of nitrogen pentoxide in
carbon tethrachloride (CCl4) solvent at 45 °C is 5.7 x 10-4
s-1 and the reaction:
2 N2O5(CCl4) ® 4 NO2(g) + O2(g)
Calculate
the half – life of the decomposition of N2O5.
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12.
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The
thermal decomposition of phosphine (PH3) into phosphorus and molecular
hydrogen is a first order reaction:
4 PH3 (g) ® P4 (g) + 6 H2(g)
The
half – life of the reaction is 35.0 s at 680 °C. Calculate:
(i)
The first – order rate constant for the reaction
(ii)
The time required for 95 percent of the phosphine
to decompose.
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13.
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Iodine
atoms combine to form molecular iodine in the gas phase
I(g)
+ I(g) ® I2(g)
This
reaction follows second order kinetics and has the high rate constant 7.0 x
109 /M.s at 23 °C.
(i)
If the initial concentration of I was 0.086 M,
calculate the concentration after 2.0 min.
(ii)
Calculate the half – life of the reaction if the
initial concentration of I is 0.60 M and if it is 0.42 M.
(iii)
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14.
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The
reaction 2A ® B is second order with a rate constant of
51 M-1min-1 at 24 °C.
(i)
Starting with [A]0 = 0.0092 M, how long
will it take for [A]t = 3.7 x 10-3 M?
(ii)
Calculate the half – life of the reaction.
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