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Chapter 16: Problem 2

Explain the difference between a reaction rate and a rate law.

Short Answer

Expert verified
Reaction rate is the speed at which a chemical reaction occurs, measured as the rate of change of concentration per unit time. On the other hand, rate law is an equation that connects the rate of reaction with the concentrations of reactants, where the rate equals a constant times each concentration to the power of a number (order of reaction). Thus, reaction rate focuses on the speed while rate law explains how this rate is influenced by the reactant concentrations.

Step by step solution

01

Define reaction rate

Reaction rate refers to the speed at which reactants are converted into products in a chemical reaction. It's usually measured as the rate of change of concentration of a reactant or product per unit time. For instance, if \(A\) transforms into \(B\), the reaction rate can be expressed as - \(\frac{d[A]}{dt}\) for reactant \(A\) and \(\frac{d[B]}{dt}\) for product \(B\).
02

Define rate law

Rate law is an equation that illustrates the relationship between the rate of a chemical reaction and the concentration of the reactants present. It is experimentally determined and often written in the form: rate = \(k[A]^x[B]^y\) where \(k\) is the rate constant, \(x\) and \(y\) are the orders of reaction with respect to reactants \(A\) and \(B\) respectively.
03

Compare reaction rate and rate law

While reaction rate quantifies the speed of a reaction, rate law further provides a mathematical description of how that rate depends on the concentration of each reactant involved. Rate law hence plays an integral role in determining the reaction rate.

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Most popular questions from this chapter

Calculate the rate of a reaction, knowing that a graph of the concentration of a product versus time had a slope of \(3.6 \times 10^{-6} \mathrm{M} / \mathrm{s}\) . The product had a coefficient of 2 .

What are enzymes, and what common features do they all share?

What is the rate of the reaction $$2 \mathrm{NO}(g)+\mathrm{Br}_{2}(g) \rightarrow 2 \mathrm{NOBr}$$ given that the bromine concentration decreased by \(5.3 \times 10^{-5} \mathrm{M}\) during an interval of 38 \(\mathrm{s} ?\)

The graphing calculator can run a program that can tell you the order of a chemical reaction, provided you indicate the reactant concentrations and reaction rates for two experiments involving the same reaction. Go to Appendix C. If you are using a TI-83 Plus, you can download the program RXNORDER and run the application as directed. If you are using another calculator, your teacher will provide you with key-strokes and data sets to use. At the prompts, enter the reactant concentrations and reaction rates. Run the program as needed to find the order of the following reactions. (All rates are given in M/s.) a. \(2 \mathrm{N}_{2} \mathrm{O}_{5}(g) \rightarrow 4 \mathrm{NO}_{2}(g)+\mathrm{O}_{2}(g)\) \(\mathrm{N}_{2} \mathrm{O}_{5} :\) conc. \(1=0.025 \mathrm{M} ;\) conc. \(2=0.040 \mathrm{M}\) rate \(1=8.1 \times 10^{-5} ;\) rate \(2=1.3 \times 10^{-4}\) b. \(2 \mathrm{NO}_{2}(g) \rightarrow 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g)\) \(\mathrm{NO}_{2} : \mathrm{conc.} 1=0.040 \mathrm{M} ; \mathrm{conc} .2=0.080 \mathrm{M}\) rate \(1=0.0030 ;\) rate \(2=0.012\) c. \(2 \mathrm{H}_{2} \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(g)+\mathrm{O}_{2}(g)\) \(\mathrm{H}_{2} \mathrm{O}_{2} :\) conc. \(1=0.522 \mathrm{M} ;\) conc. \(2=0.887 \mathrm{M}\) rate \(1=1.90 \times 10^{-4} ;\) rate \(2=3.23 \times 10^{-4}\) d. \(2 \mathrm{NOBr}(g) \rightarrow 2 \mathrm{NO}(g)+\mathrm{Br}_{2}(g)\) NOBr: conc. \(1=1.27 \times 10^{-4} \mathrm{M} ;\) conc. \(2=\) \(4.04 \times 10^{-4} \mathrm{M}\) rate \(1=6.26 \times 10^{-5} ;\) rate \(2=6.33 \times 10^{-4}\) e. \(2 \mathrm{HI}(g) \rightarrow \mathrm{H}_{2}(g)+\mathrm{I}_{2}(g)\) HI: conc. \(1=4.18 \times 10^{-4} \mathrm{M} ;\) conc. \(2=\) \(8.36 \times 10^{-4} \mathrm{M}\) rate \(1=3.86 \times 10^{-5} ;\) rate \(2=1.54 \times 10^{-4}\)

Why are reaction orders not always equal to the coefficients in a chemical equation?
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