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Ch.14 - Chemical Kinetics
Brown - Chemistry: The Central Science 14th Edition
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Tutti i libri di testoBrown 14th EditionCh.14 - Chemical KineticsProblema 35d
Capitolo 14, Problema 35d

The following data were measured for the reaction BF3(g) + NH3(g) → F3BNH3(g):
Experiment [BF3] (M) [NH3] (M) Initial Rate (M/s)
1 0.250 0.250 0.2130
2 0.250 0.125 0.1065
3 0.200 0.100 0.0682
4 0.350 0.100 0.1193
5 0.175 0.100 0.0596
(d) What is the rate when [BF3] = 0.100 M and [NH3] = 0.500 M?

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1
Identify the rate law for the reaction. The rate law can be expressed as: Rate = k[BF3]^m[NH3]^n, where k is the rate constant, and m and n are the orders of the reaction with respect to BF3 and NH3, respectively.
Use the experimental data to determine the reaction orders m and n. Compare experiments where only one concentration changes while the other remains constant to find the order with respect to each reactant.
For example, compare experiments 1 and 2 to find the order with respect to NH3. The concentration of BF3 is constant, so the change in rate is due to the change in NH3 concentration. Use the formula: (Rate1/Rate2) = ([NH3]1/[NH3]2)^n to solve for n.
Similarly, compare experiments 3 and 4 to find the order with respect to BF3. The concentration of NH3 is constant, so the change in rate is due to the change in BF3 concentration. Use the formula: (Rate3/Rate4) = ([BF3]3/[BF3]4)^m to solve for m.
Once the orders m and n are determined, use any experiment to solve for the rate constant k. Substitute the values of m, n, and the concentrations and rate from one experiment into the rate law equation to find k. Finally, use the rate law with the determined k, m, and n to calculate the rate for [BF3] = 0.100 M and [NH3] = 0.500 M.

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Rate Law

The rate law expresses the relationship between the rate of a chemical reaction and the concentration of its reactants. It is typically formulated as Rate = k[A]^m[B]^n, where k is the rate constant, [A] and [B] are the concentrations of the reactants, and m and n are the reaction orders. Understanding the rate law is essential for predicting how changes in concentration affect the reaction rate.
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Rate Law Fundamentals

Reaction Order

Reaction order refers to the exponent in the rate law that indicates how the rate of reaction depends on the concentration of a particular reactant. It can be determined experimentally and can be zero, first, second, or even fractional. The overall order of the reaction is the sum of the individual orders, which helps in understanding the kinetics of the reaction.
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Average Bond Order

Method of Initial Rates

The method of initial rates involves measuring the initial rate of reaction at varying concentrations of reactants to deduce the rate law and reaction orders. By analyzing how the initial rate changes with different concentrations, one can derive the values of m and n in the rate law. This method is crucial for determining the kinetics of the reaction in question.
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Percorso guidato
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Rate Law Determination
Pratica correlata
Domanda del libro di testo

The following data were measured for the reaction BF3(g) + NH3(g) → F3BNH3(g):

Experiment [BF3] (M) [NH3] (M) Initial Rate (M/s)

1 0.250 0.250 0.2130

2 0.250 0.125 0.1065

3 0.200 0.100 0.0682

4 0.350 0.100 0.1193

5 0.175 0.100 0.0596 

(c) Calculate the rate constant with proper units?

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Domanda del libro di testo

The following data were measured for the reaction BF3(g) + NH3(g) → F3BNH3(g):

Experiment [BF3] (M) [NH3] (M) Initial Rate (M/s)

1 0.250 0.250 0.2130

2 0.250 0.125 0.1065

3 0.200 0.100 0.0682

4 0.350 0.100 0.1193

5 0.175 0.100 0.0596 

(b) What is the overall order of the reaction?

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Domanda del libro di testo

Consider the gas-phase reaction between nitric oxide and bromine at 273°C: 2 NO(g) + Br2(g) → 2 NOBr(g). The following data for the initial rate of appearance of NOBr were obtained:

Experiment [NO] (M) [Br2] (M) Initial Rate (M/s)

1 0.10 0.20 24

2 0.25 0.20 150

3 0.10 0.50 60

4 0.35 0.50 735 

(b) Calculate the average value of the rate constant for the appearance of NOBr from the four data sets.

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