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WORKSHEET 6

Calculating Reaction Rates

For each of the following reactions

a) Write the predicted rate law from the balanced equation.

b) Write the real rate law using the information provided.

c) Give the order of reaction.

d) Give the overall order of reaction.

| |Reaction |Rate dependent on |

|1. |A + B ( products |[A]2 |[B]1 |

|2. |2NO(g) + O2(g) ( NO2(g) |[NO]1 |[O2]1 |

|3. |2NO(g) + 2H2(g) ( N2(g) + 2H2O(g) |[NO]2 |[H2]1 |

|4. |2NO2(g) + Cl2(g) ( 2NO2Cl(g) |[NO2]1 |[Cl2]1 |

|5. |2ClO2(aq) + 2OH-(aq) ( ClO3-(aq) + ClO2-(aq) + H2O(l) |[ClO2]0 |[OH-]1 |

|6. |C + D ( products |[C]2 |[D]0 |

7. For the following reaction the data in the table was obtained.

S2O82-(aq) + 2I-(aq) ↔ 2SO42-(aq) + I2(aq)

|Trial |Initial [S2O82-] |Initial [I-] |Initial Rate |

|1 |1.0 x 10-4 |1 x 10-2 |0.65 x 10-6 mol/dm3/s |

|2 |2.0 x 10-4 |1 x 10-2 |1.30 x 10-6 mol/dm3/s |

|3 |2.0 x 10-4 |0.5 x 10-2 |0.65 x 10-6 mol/dm3/s |

a) What is the predicted rate?

b) What is the experimental rate?

c) Calculate the value of the rate constant?

d) What is the overall order of the reaction?

8. For a reaction of A + B to form C the following data were obtained from three experiments:

|Trial |Initial [A] |Initial [B] |Initial Rate |

|1 |0.20 |0.20 |3 x 10-4 mol/dm3/min |

|2 |0.60 |0.60 |81 x 10-4 mol/dm3/min |

|3 |0.60 |0.20 |9 x 10-4 mol/dm3/min |

a) What is the rate expression for the reaction?

b) What is the numerical value of the rate constant, k?

c) Give a plausible equation for the rate-determining step.

9. For the hypothetical reaction: 2A + 3B ↔ 3C + 2D the following data were obtained in three experiments at the same temperature.

|Trial |Initial [A] |Initial [B] |Initial Rate |

|1 |0.10 |0.10 |0.10 mol/dm3/s |

|2 |0.20 |0.10 |0.40 mol/dm3/s |

|3 |0.20 |0.20 |0.40 mol/dm3/s |

a) What is the predicted rate of this reaction?

b) Determine the experimental rate expression.

c) Calculate the value of “k”?

d) What is the rate of this reaction when [A] = 0.30 mol·dm-3 and

[B] = 0.30 mol·dm-3

e) Give a possible mechanism for this reaction and indicate the rate determining

step.

10. For hypothetical reaction: 2A + 2B ↔ 3C, the following data were collected.

|Trial |Initial [A] |Initial [B] |Initial Rate |

|1 |0.10 |0.20 |300 mol/dm3/min |

|2 |0.30 |0.40 |3600 mol/dm3/min |

|3 |0.30 |0.80 |14400 mol/dm3/min |

a) What is the predicted rate?

b) What is the experimental rate equation for this reaction?

c) Calculate the rate constant “k”.

d) What is the rate of this reaction when [A] = 0.20 mol·dm-3 and

[B] = 0.30 mol·dm-3 ?

11. Use the following data to answer question a – c for the reaction:

4NO2(g) + O2(g) ↔ 2N2O5(g)

|Trial |Initial [NO2] |Initial [O2] |Initial Rate |

|1 |0.025 |0.011 |3.1 x 10-4mol/dm3/s |

|2 |0.025 |0.022 |6.2 x 10-4 mol/dm3/s |

|3 |0.050 |0.011 |6.2 x 10-4 mol/dm3/s |

a) Write the rate law expression for the reaction

b) Determine the overall order of the reaction.

c) Calculate the rate constant.

d) Use the rate law expression and calculated value of k to compute the initial rate of formation of N2O5 if the initial concentration of NO2 is 0.030 mol·dm-3 and the concentration of O2 is 0.044 mol·dm-3.

12. Assume that NO(g) and H2(g) react according to the rate law: Rate = k[NO]2[H2].

How does the rate change if

a) the concentration of H2 is doubled?

b) the volume of the enclosing vessel is suddenly halved?

c) the temperature is decreased?

13. The following data which were taken for the reaction A + B + C ↔ Products

|Trial |Initial [A] |Initial [B] |Initial [C] |Initial Rate |

|1 |0.15 |0.010 |0.12 |0.024 mol/dm3/min |

|2 |0.15 |0.010 |0.24 |0.048 mol/dm3/min |

|3 |0.30 |0.010 |0.24 |0.048 mol/dm3/min |

|4 |0.30 |0.020 |0.24 |0.192 mol/dm3/min |

a) What is the rate law?

b) What is the value of the rate constant?

c) What is the order of the reaction with respect to B?

d) What is the overall order of the reaction?

e) What is the rate when [A] is 0.20 mol·dm-3, [B] is 0.40 mol·dm-3, and

[C] is 0.15 mol·dm-3?

14. Nitrogen monoxide reacts with oxygen to produce nitrogen dioxide. Using the following data, calculate

a) the overall order of the reaction

b) the rate law expression

c) the value of the rate constant

d) the rate of the reaction if [NO] =0.035 and [O2] = 0.25

2NO(g) + O2(g) ↔ 2NO2(g)

|Trial |Initial [NO] |Initial [O2] |Initial Rate |

|1 |0.015 |0.010 |0.0041 mol/dm3/s |

|2 |0.030 |0.010 |0.0164 mol/dm3/s |

|3 |0.015 |0.020 |0.0082 mol/dm3/s |

15. For the hypothetical reaction: A + 2B + C ↔ Products, the following data were taken:

|Trial |Initial [A] |Initial [B] |Initial [C] |Initial Rate |

|1 |0.010 |0.010 |0.020 |0.00012 mol/dm3/s |

|2 |0.020 |0.010 |0.020 |0.00024 mol/dm3/s |

|3 |0.010 |0.020 |0.020 |0.00048 mol/dm3/s |

|4 |0.020 |0.010 |0.010 |0.00024 mol/dm3/s |

a) What is the rate law for the reaction? What is the overall order of the reaction?

b) What is the value for the rate law constant?

c) What is the rate of the reaction if [A] = 0.025, [B] = 0.015, and [C] = 0.030?

Answers:

1a) r = k[A][B] b) r = k[A]2[B] c) A = 2, B = 1 d) third order

2a) r = k[NO]2[O2] b) r= k[NO][O2] c) NO = 1, O2 = 1 d) second order

3a) r = k[NO]2[H2]2 b) r = k[NO]2[H2]1 c) NO = 2, H2 = 1 d) third order

4a) r = k[NO2]2[Cl2] b) r = k[NO2][Cl2] c) NO2 = 1, Cl2 = 1 d) second order

5a) r = k[ClO2]2[OH-]2 b) r = k[OH-] c) OH- = 1 d) first order

6a) r = k[C][D] b) r = k[C]2 c) C = 2 d) second order

7a) r = k[S2O82-][I-]2 b) r = k[S2O82-][I-] c) k = 0.65 dm3/mol/s d) second order

8a) r = k[A][B]2 b) 0.038 dm6/mol2/s c) A + 2B (

9a) r = k[A]2[B]3 b) r = k[A]2 c) k = 10 dm3/mol/s d) 0.9 mol/dm3/s

e) 2A ( X + 2D, X + B ( Y + B, Y + B ( Z + C, Z + B ( C

10a) r = k[A]2[B]2 b) r = k[A][B]2 c) 7.5 x 104 dm6/mol2/s d) r = 1350 mol/dm3/s

11a) r = k[NO2][O2] b) second order c) k = 1.1 dm3/mol/s d) r = 1.5 x 10-3 mol/dm3/s

12a) doubles b) x8 c) not enough information

13a) r = k[B]2[C] b) k = 2000 dm6/mol2/s c) 2 d) third order e) r = 48 mol/dm3/s

14a) r = k[NO]2 b) NO = 2 c) k = 18 dm3/mol/s d) r = 0.022 mol/dm3/s

15a) r = k[A][B]2 b) third order c) k = 120 dm6/mol2/s d) r = 6.8 x 10-4 mol/dm3/s

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