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Chapter 16: Q16.9 P (page 728)

Give two reasons to measure initialrates in a kinetic study.

Short Answer

Expert verified

The answer is,

1) To calculate the overall rate of a reaction.

2) To calculate many other kinetic parameters.

Step by step solution

01

Rate of a reaction

The rate of a reaction is the speed at which the reactants undergo product formation at a constant temperature. The initial rate is the rate at the initial point of the reaction, where the reactant concentration is introduced.

02

Explanation

The two reasons to measure the initial rate in a kinetic study is as given below.

1) The overall rate of a reaction is calculated by measuring the rate of the forward reaction and that of the reverse reaction and taking the difference of both. This is done by finding the initial rate, the instantaneous rate at the initial point of addition of reactants to avoid complications of the calculations.

2) The initial rate of the reaction is used to calculate many other kinetic parameters.

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Most popular questions from this chapter

Question:Many drugs decompose in blood by a first-order process.

(a) Two tablets of aspirin supply 0.60 g of the active compound. After 30 min, this compound reaches a maximum concentration of 2 mg/100 mL of blood. If the half-life for its breakdown is 90 min, what is its concentration (in mg/100 mL) 2.5 h after it reaches its maximum concentration?

(b) For the decomposition of an antibiotic in a person with a normal temperature (98.6°F),k=3.1×10-5s-1; for a person with a fever at 101.9°F, k=3.9×10-5s-1. If the person with the fever must take another pill when of the first pill has decomposed, how many hours should she wait to take a second pill? A third pill? (Assume the pill is effective immediately.)

(c) Calculate Ea for decomposition of the antibiotic in part (b).

Define reaction rate, assuming constant temperature and a closed reaction vessel, why does the rate change with time?

Even when a mechanism is consistent with the rate law, later work may show it to be incorrect. For example, the reaction between hydrogen and iodine has this rate law: rate=k[H2][I2] . The long-accepted mechanism had a single bimolecular step; that is, the overall reaction was thought to be elementary:

H2(g)+I2(g)→2HI(g)

In the 1960s, however, spectroscopic evidence showed the presence of free I atoms during the reaction. Kineticists have since proposed a three-step mechanism:

(1)I2(g)⇌2I(g)[fast](2)H2(g)+I(g)⇌H2I(g)[fast](3)H2I(g)+I(g)⇌2HI(g)[slow]

Show that this mechanism is consistent with the rate law.

Reaction rate is expressed in terms of changes in the concentration of reactants andproducts. Write a balanced equation for

Rate=-12∆[N2O5]∆t=14∆[NO2]∆t=∆[O2]∆t

Like any catalyst, palladium, platinum, and nickel catalyze both directions of a reaction: the addition of hydrogen to (hydrogenation) and its elimination from (dehydrogenation) carbon double bonds.

(a) Which variable determines whether an alkene will be hydrogenated or dehydrogenated?

(b) Which reaction requires a higher temperature?

(c) How can all-trans fats arise during the hydrogenation of fats that contain some cis-double bonds?
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