Chemistry

Name: _______________________________

REACTION KINETICS WORKSHEET #3 1.

It is known that compounds called chlorofluorocarbons (CFCs) (eg. CFCl3) will break up in the presence of ultraviolet radiation, such as found in the upper atmosphere, forming single chlorine atoms:

CFCl3  CFCl2 + Cl

The Cl atoms then react with Ozone (O3) as outlined in the following mechanism. Step 1: Cl + O3  ClO + O2 Step 2: ClO + O  Cl + O2

(single "O" atoms occur naturally in the atmosphere)

a) Write the equation for the overall reaction.____________________________ b) What is the catalyst in this reaction? _________________________________ c) Identify an intermediate in this reaction._______________________________ d) Explain how a small amount of CFCs can destroy a large amount of ozone. __________________________________________________________________ __________________________________________________________________ e) What breaks the bond in the CFCl3 and releases the free Cl atom?__________ 2.

Given the following mechanism, answer the questions below: Step 1: O3 + NO  NO2 + O2 (slow) Step 2: NO2 + O  NO + O2

(fast)

a) Give the equation for the overall reaction._______________________________ b) Identify the catalyst ___________ and the intermediate ____________ c) Which reaction is the rate determining step?____________________________ d) The uncatalyzed overall reaction is a slow exothermic reaction, draw a potential energy diagram which shows the possible shape of the curve for the uncatalyzed reaction. On the same graph, show a possible curve for the catalyzed reaction

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Chemistry

Name: _______________________________

3. Given the following Potential Energy Diagram for a 3-step reaction, answer the questions below it:

POTENTIAL ENERGY

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5 3 4

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PROGRESS OF REACTION Identify which arrow indicates: a) The activation energy for the first step of the reverse reaction?____________ b) The activation energy for the first step of the forward reaction?____________ c) The activation energy for the second step of the forward reaction?__________ d) The enthalpy change (∆H) for the overall forward reaction? __________ e) The enthalpy change (ΔH) for the overall reverse reaction? _________

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Chemistry 4.

Name: _______________________________

A reaction has the following reaction mechanism, EA values and ΔH values: Step 1: A + B  C + E

EA = +45 kJ

ΔH = -72 kJ

Step 2: A + E  2D

EA = +80 kJ

ΔH = +28 kJ

a) Give the equation for the overall reaction. ______________________________ b) The rate determining step is _____ because____________________________ c) What is the effect on the overall reaction rate of increasing the concentration of (i)

substance A? Explain.___________________________________________________

(ii)

substance B? Explain____________________________________________________

d) For the overall reaction, EA = _______ and ΔH = _______ e) Is the overall reaction endothermic or exothermic? ______________________ f) Draw a complete potential energy diagram for the 2-step reaction mechanism.

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