Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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.