Name ____Mr. Perfect______Date ___Sp 15______

1. Consider the following reaction between monoxide and :

2 NO + Cl2 → 2 NOCl

From the following data, determine the rate law for the reaction and state the overall order of the reaction. Also, calculate the rate constant for the reaction (include proper units for full credit). (15 pts)

Trial [NO] (M) [Cl2] (M) Initial Rate (M/s) Rate Law: 1 0.13 0.20 1.0 x 10-2 -2 x y 2 0.26 0.20 4.0 x 10 Rate = k[NO] [Cl2] 3 0.13 0.10 5.0 x 10-3

4 = 2x 2 = 2y

x = 2 second-order in NO y = 1 first-order in Cl2 Rate Law: 2 Rate = k[NO] [Cl2] third-order overall

2. Write the possible rate expressions for each the following reactions: (10 pts)

a) N2 + 3 H2 → 2 NH3

b) 4 NH3 + 5 O2 → 4 NO + 6 H2O

3. Write the balanced equation that corresponds to the following rate expressions: (5 pts)

2 NO + Br2 → 2 NOBr

Chemistry 102 Exam 1 Name ____Mr. Perfect______Date ___Sp 15______

4. The overall reaction for the decomposition of dinitrogen pentoxide is shown below and has the 2 experimental rate law: Rate = k[N2O5] [NO3]

N2O5 + NO3 → 3 NO2 + O2

Clearly show that the following proposed mechanism is either correct or incorrect: (10 pts)

Proposed Mechanism

k1

Step 1: N2O5 ⇄ NO2 + NO3 k- 1 k2 Step 2: NO2 + NO3 → NO + NO2 + O2 (Slow Step) Rate Determining Step

k3 Step 3: NO + NO3 → 2 NO2 ______

N2O5 + NO3 → 3 NO2 + O2 overall reaction Rate = k2[NO2][NO3] Solve for the intermediate NO2 (k1[N2O5] = k-1[NO2][NO3])

Substitute into the rate law:

Mechanism is not valid because the proposed mechanism rate law does not equal the experimental rate law.

5. The partial pressures in an equilibrium mixture of NO, Cl2, and NOCl at 500 K are: PNO =

0.240 atm, PCl2 =0.608 atm, PNOCl = 1.35 atm. Calculate the equilibrium constant, Kp, for the following reaction: (10 pts)

2 NO(g) + Cl2(g) ⇄ 2 NOCl(g)

Chemistry 102 Exam 1 Name ____Mr. Perfect______Date ___Sp 15______

6. A 9.30 x 10-3 mol sample of HI was placed in an empty 2.00 L container at 1000 K. After -4 equilibrium was established, the concentration of I2 was 6.29 x 10 M. Calculate the value of Kc for the following reaction: (10 pts)

H2(g) + I2(g) ⇄ 2 HI(g) -3 -3 Reverse the equation: [HI] = 9.30 x 10 mol/2.00 L = 4.65 x10 M 2 HI ⇄ H2 + I2 I 4.65 x10-3 0 0 Given C -2x +x +x x = 6.29 x 10-4 M E 4.65 x10-3-2x x x Substitute x into the equation:

7. Calculate the value of Kc when 1.00 mol of PCl5 is placed into a 5.00 L container at 500 K, 78.5 % of the PCl5 dissociates to give the following equilibrium: (10 pts) [PCl5] = 1.00 mol/5.00 L = 0.20 M

PCl5(g) ⇄ PCl3(g) + Cl2(g) I 0.2 0 0 C -x +x +x E 0.2-x x x x = 0.2(0.785) = 0.157 M Substitute x into the equation

8. The vapor pressure of water at 25 °C is 23.8 mmHg. Calculate the values of Kp and Kc at 25 Δn °C for the following equilibrium: (10 pts) Kp = Kc(0.0821 x T)

H2O(l) ⇄ H2O(g) Convert pressure to atm and temperature to Kelvin:

Chemistry 102 Exam 1 Name ____Mr. Perfect______Date ___Sp 15______

9. The decomposition of to molecular and water is a first-order reaction. If it takes 8.0 hrs for the concentration of H2O2 to decrease from 0.80 M to 0.40 M, how many hours are required for the concentration to decrease from 0.60 M to 0.15 M? (10 pts) Some useful equations: Integrated First –Order rate law

[A]t = -kt + [A]o 1/[A]t = kt + 1/[A]o ln[A]t = -kt + ln[A]

H2O2(aq) ⇄ H2O(l) + O2(g)

First solve for k:

( )

Solve for time:

( )

-1 -1 10. Rate constants for the reaction of NO2(g) + CO(g) → NO(g) + CO2(g) are 1.3 M s at 700 K and 23.0 M-1s-1 at 800 K. Calculate the activation energy for this reaction in kJ/mol. (10 pts)

( )

( )

2.87(8.314 J/molK) = (1.79 x 10-4)Ea

Ea = 133784 J/mol = 134 kJ/mol

11. Extra Credit. Predict the effect on the following equilibrium when a catalyst is added into the reaction mixture. (5 pts)

NO2Cl(g) + NO(g) ⇄ NOCl(g) + NO2(g)

A catalyst will cause the system to reach equilibrium faster but has no effect on the equilibrium.

Chemistry 102 Exam 1