Download Chemistry 12 Take Home Assignment /23

Chemistry 12
Take Home Assignment
/23
1. It is known that compounds called chlorofluorocarbons (C.F.C.s) (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. (Using steps 1 and 2)
_________________________________________________________
(1 pt)
b) What is the catalyst in this reaction? ________________________
(0.5 pts)
c) Identify an intermediate in this reaction______________________
(0.5 pts)
d) What breaks the bond in the CFCl3 and releases the free Cl atom?____________
(0.5 pts)
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.
_________________________________________________________________
(1 pt)
b) What could the catalyst be in this mechanism? ________________________
(0.5 pts)
c) What is an intermediate in this mechanism? ______________________________
(0.5 pts)
d) Given that the uncatalyzed overall reaction is a slow exothermic reaction, draw a potential energy graph
which shows the possible shape of the curve for the uncatalyzed reaction. On the same graph, show a possible
curve for the catalyzed reaction.
(2 pts)
3. Consider the following mechanism:
Step 1: H2O2 + I- H2O + IO- (slow)
Step 2: H2O2 + IO- H2O + O2 + I- (fast)
a) Give the equation for the overall reaction.
(1 pt)
__________________________________________________________________
b) What acts as a catalyst in this mechanism? _________________________________
(0.5 pts)
c) What acts as an intermediate in this mechanism? ____________________________
(0.5 pts)
4. What is meant by the rate determining step in a reaction mechanism?
(1 pt)
____________________________________________________________________
____________________________________________________________________
5. Given the following Potential Energy Diagram for a 3 step reaction, answer the questions below it: (3.5 pts)
a) Which arrow indicates the activation energy for the first step of the reverse reaction?________
b) Which arrow indicates the activation energy for the first step of the forward reaction?____
c) Which arrow indicates the activation energy for the second step of the forward reaction?________
d) Which arrow indicates the enthalpy change (∆H) for the overall forward reaction? ________
e) Which arrow indicates the enthalpy change (∆H) for the overall reverse reaction? ________
f) Which arrow indicates the activation energy for the overall forward reaction?
________
g) Which step would be the rate determining step in the forward reaction?
________
6) The graph below shows the energy changes involved in an uncatalyzed and a catalyzed reversible reaction.
Match the following descriptions to the numbers on the graph. Note: Some numbers do not have matching
descriptions.
(2.5 pts)
(a) ______ activation energy of the first step of the forward catalyzed reaction.
(b) ______ overall change in energy for the reaction.
(c) ______ activation energy of the forward uncatalyzed reaction.
(d) ______ transition state.
(e)
_____ activation energy of the reverse uncatalyzed reaction.
7) The reaction NO2(g) + CO(g) → CO2(g) + NO(g) occurs in a single step at 600oC. At temperatures below 500OC,
the following mechanism is proposed:
step 1
step 2
2NO2(g) → NO(g) + NO3(g)
NO3(g) + CO(g) → CO2(g) + NO2(g)
slow
fast
Suggest a reason for this difference in mechanisms at the different temperatures.
(1.5 pts)
8) Why is the following reaction not likely to take place in one step? Explain.
(1.5 pts)
4HBr(g) + O2 (g) → 2H2O (g) + Br2 (g)
9) Given the reaction Zn (s) + 2HCl
→ ZnCl2 (aq) + H2 (g). What would be the effect on the rate of the reaction if:
(1.5 pts)
a) Powdered zinc was added to the acid instead of a solid piece of zinc metal.
(aq)
b) The concentration of HCl
(aq)
was doubled.
c) A catalyst was introduced to the system.
10) Which of the five factors that affect the rate of reaction is illustrated in each of the following: (Be sure to
explain why)
(3 pts)
a) Food is sometimes frozen before it is used.
b) Small sticks of wood are often used to start a fire.
c) In hospitals, the healing process is often quickened in an oxygen tent.