GENERAL CHEMISTRY 128

EXAM I

NAME: ______

  1. List the four variables or factors than can affect the rate of reaction.

a. ______c. ______

b. ______d. ______

  1. A reaction believed to be either first or second order has a half-life of 20 s at the beginning of an experiment but of 40 s some time later. What is the order of the reaction? Circle one: first or second
  1. The rate law for the overall reaction 2NO2Cl(g) à 2NO2(g) + Cl2(g) is first order for nitryl chloride, NO2Cl.

Explain why the mechanism for this reaction cannot be the single elementary reaction: 2NO2Cl(g) à 2NO2(g) + Cl2(g).

4. Iron(III) ion is reduced by tin(II) ion according to the reaction below.

2Fe3+ (aq) + Sn2+(aq) à 2Fe2+(aq) + Sn4+(aq)

The concentration of Fe3+ ion at the beginning of an experiment was 0.03586 M. After 4.00 min, it was 0.02638 M. What is the average rate of reaction of Fe3+ in this time interval?

Average rate of reaction of Fe3+: ______

What is the average rate of appearance of Sn4+: ______

What is the average rate of reaction: ______

5. For the reaction of iron(II) ion with hydrogen peroxide in an acidic solution, what is the rate law?

H2O2(aq) + 2Fe2+(aq) + 2H+(aq) à 2Fe3+(aq) + 2H2O(l )

H2O2 / Fe2+ / H+ / Initial Rate
Experiment 1 / 0.0125 M / 0.0250 M / 0.0100 M / 0.0561 mol/Ls
Experiment 2 / 0.0125 M / 0.0125 M / 0.0100 M / 0.0281 mol/Ls
Experiment 3 / 0.0250 M / 0.0125 M / 0.0100 M / 0.1129 mol/Ls
Experiment 4 / 0.0375 M / 0.0250 M / 0.0100 M / 0.2520 mol/Ls
Experiment 5 / 0.0375 M / 0.0250 M / 0.0300 M / 0.2522 mol/Ls

Rate law: ______

Order with respect to Fe2+: ______

6. Cyclobutane, C4H8, consisting of molecules in which four carbon atoms form a ring, decomposes, when heated, to give ethylene, C2H4.

C4H8(g) à 2C2H4(g)

The reaction is first order. In an experiment, the initial concentration of cyclobutane was 0.00150 M. After heating at 450oC for 455 s, this was reduced to 0.00119 M. What was the concentration of cyclobutane after a total of 968 s?

Concentration after 968 s: ______

7. If the reaction of C2H4O(g) à CH4(g) + CO(g) is second order reaction and if the concentration in an experiment is reduced from 0.200 M to 0.129 M in 225 seconds, what is the rate constant with units for the reaction?

Rate constant: ______

What is the half-life of this reaction: ______

8.  What is the molecularity of the reaction NOCl2 + NO à 2NOCl? ______

9. The thermal decomposition of nitryl bromide, NO2Br, is represented by this reaction:

2NO2Br(g) à 2NO2(g) + Br2(g) (overall reaction)

The mechanism is thought to be:

NO2Br NO2 + Br fast step

NO2Br + Br à NO2 + Br2 slow step

What is the rate law predicted by this mechanism?

Rate law: ______

What is Br in this mechanism? ______

10. Write the equilibrium expression for the reaction

2Cu(NO3)2(s) 2CuO(s) + 4NO2(g) + O2(g)

Equilibrium expression: ______


11. Draw a graph of how the rates of A and B change in the equilibrium reaction

A B

Indicate on the graph the region that shows that equilibrium has been reached.

12. The equilibrium constant, Kc, for the equation 2HI(g) H2(g) + I2(g) is 1.84.

Does this reaction favor the products or favor the reactants? ______

After equilibrium has been reached, if I2(g) is removed, in which direction will the reaction shift? ______

What is the value of Kc for the reaction:

H2(g) + I2(g) 2HI(g)

Kc: ______


13. For the reaction 2HF(g) H2(g) + F2(g) if the equilibrium constant is 1.0 x 10-4, and if a 6.0 L flask contained 2.5 moles of HF, what is the equilibrium concentration of F2(g)?

Equilibrium concentration of F2: ______

I have neither cheated not have I seen anyone else cheating during or before this exam.

Signature ______