## CHAPTER 13 REGULAR HOMEWORK

### KINETICS II

**Question 1**

^{x}[B]

^{y}. What are x and y, that is, what is the order of reaction with respect to A and B?

Select one or more:

**Explanation**

**Question 2**

Determine the rate constant from the concentration-time dependence (The units for the initial rate of reaction are Ms^{-1}):

[A] | [B] | Init. Rate |

0.020 | 0.15 | 0.055 |

0.035 | 0.15 | 0.096 |

0.050 | 0.35 | 0.75 |

**Explanation**

**Question 3**

_{2}(g) At 450 K the rate constant is 15.4 atm

^{-1}s

^{-1}. How much time (in s) is needed for NOCl originally at a partial pressure of 47 torr to decay to 29.5 torr?

**Explanation**

- Convert torr to atm (this is done because our k value is in atm)
- Treat the atm values as you would concentration and use the second order integrated rate law to solve for t (seconds needed)

**Question 4**

**Explanation**

**Question 5**

The decomposition of formic acid (see below) is measured at several temperatures. HCOOH(g) → CO_{2}(g) +H_{2}(g) The temperature dependence of the first-order rate constant is: T(K) . . . . k(s^{-1})

800 ....0.00027 825 ....0.00049 850 ....0.00086 875 ....0.00143 900 ....0.00234 925 ....0.00372

Calculate the activation energy, in kJ/mol. Use all data points and do a linear regression using calculator or Excel. Do not pick 2 data points. This is less accurate and assumes all data points are equally good.

**Explanation**

**Question 6**

^{-1}).

**Explanation**

**Question 7**

**Explanation**

**Question 8**

**Explanation**

**Question 9**

**Explanation**

**Question 10**

**Explanation**

**Question 11**

**Explanation**

N2O4 is the intermediate because it is created and consumed within the reaction-is not a reactant nor a product. This question is slightly different than the previous one in that the slow step depends on the products of the fast step to occur–an important distinction.

- N2O4 is made from two molecules of NO2 (in the reversible fast reaction) and so its concentration will depend on the concentration of NO2.
- That means that you can replace [N2O4] by [2NO2]
- Our initial rate equation for the slow reaction was:

- Our new rate equation (with replacement) is:

**Question 12**

**Explanation**

**Question 13**

**Explanation**

**Question 14**

**Explanation**

**Question 15**

**Explanation**

**Question 16**

**Explanation**

**Question 17**

_{2}(g) + H

_{2}(g) The rate of reaction is monitored by measuring the total pressure in the reaction container. Time (s) . . . P (torr) 0 . . . . . . . . . 220 50 . . . . . . . . 324 100 . . . . . . . 379 150 . . . . . . . 408 200 . . . . . . . 423 250 . . . . . . . 431 300 . . . . . . . 435 At the start of the reaction (time = 0), only formic acid is present. What is the formic acid pressure (in torr) when the total pressure is 406? Hint: use Dalton’s law of partial pressure and the reaction stoichiometry.

**Explanation**

**Question 18**

**Explanation**

__-x +x +x__220-x +2x =324 220+x=324 x=104 since x=the amount of reactant used up at 50s, 220-104= 116 torr HCOOH at 50s 2) Use first order integrated rate law to find k: ln(220/116)=-kt ln(220/116)=-k(50) k=1.28 x 10^-2 3) Use first order half life equation to find half life: t

_{½}= 0.693 / k t

_{½}=0.693/(1.28×10^-2) t

_{½=54.14}

**Question 19**

^{-1})? (To determine the rate, you must use a reactant concentration or pressure. Use the procedure of in the previous question to determine the HCOOH pressure as a function of the total pressure.)