a)
Outline two ways a rate of a reaction can be expressed and state the units for rate of reaction.
[2]
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b)
Explain what is meant by the order of a reaction and how it may be determined.
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c)
Carbon monoxide and chlorine react together to make phosgene, COCl2 . The equation for the reaction is given below:
CO (g) + Cl
2 (g) → COCl
2 ( g)
A possible rate equation for the reaction is:
rate = k[CO (g)]2 [Cl2 (g)]½
What is the overall reaction order?
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d)
Determine the units of the rate constant, k , for the following rate equation:
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a)
The rate of hydrolysis of sucrose under acidic conditions can be determined experimentally. The following data was obtained:
Experiment Initial [HCl] / mol dm-3 Initial [sucrose] / mol dm-3 Rate of reaction / mol dm-3 s-1
1
0.10
0.10
0.024
2
0.10
0.15
0.036
3
0.20
0.10
0.048
Determine the order of reaction with respect to HCl.
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b)
Determine the order of reaction with respect to sucrose.
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c)
Determine the overall order of reaction, write the rate expression and state the units of the rate constant, k .
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d)
Determine the following:
i)
The value of k, using Experiment 1
[1]
ii)
The rate of reaction if the concentration of HCl and sucrose are both 0.20 mol dm-3
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a)
Sketch graphs of a first order and second order reaction of concentration against time.
[2]
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b)
Draw sketch graphs for a first and second order reaction of rate against concentration.
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c)
Deduce the units of the rate constant, k, for a first order reaction.
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d)
State, with a reason, how the value of the rate constant, k , varies with increased temperature for a reaction.
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a)
State what is meant by the terms rate determining step and molecularity in a chemical reaction.
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b)
The following reaction mechanism has been proposed for the formation of nitrosyl bromide, NOBr, from nitrogen monoxide and bromine:
Step 1: NO + NO → N2 O2
Step 2: N2 O2 + Br2 → 2NOBr
Deduce the overall reaction equation and comment on the molecularity of Step 1 and 2.
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c)
A student proposes an alternative one step mechanism for the formation of nitrosyl bromide.
NO + NO + Br2 → NOBr2
Explain why this mechanism is not likely to take place.
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d)
State the role of N2 O2 in the mechanism in part b).
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a)
Draw a labelled diagram, on the follow grid, showing a potential energy profile in a two step reaction. The second step is the slow step of the reaction.
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b)
State which step of the mechanism in a) is affected by the addition of a catalyst.
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c)
A reaction mechanism is shown below.
Step 1: NO
2 + NO
2 → NO + NO
3 (slow)
Step 2: NO3 + CO → NO2 + CO2 ( fast)
Deduce the overall reaction equation and the rate equation for the reaction.
[2]
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d)
State the overall reaction order in part c) and state the units of the rate constant.
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