CHEM 204 Lecture Notes - Lecture 5: Molecularity, Second Order (Religious), Rate-Determining Step

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25 Jan 2018

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Chem 204 chemical kinetics: the goal of chemical kinetics is in determining the rate of a reaction and its dependence on parameters such as concentration, temperature, and catalysts. 12. 1 reaction rate: the rate of reaction is expressed as the change in a reactant concentration with time, rate is usually expressed as the rate of change in reactant concentration over time. It is also important to mention that there is no connection between the order of the reactant and the stoichiometric coefficient: for example: In the reaction: the rate equation is given by, the reaction is first order in [n2o5, the order of reaction specifies the empirical dependence on the rate concentrations. It may be zero, an integer, or a non-integer: we can use the rate law to determine the concentrations of reactants at any time during the course of the reaction.

Related Questions

What is the instantaneous rate of the reaction at t=800s?

The answer is rate= 6.8x10^-5 m/s but I need an explanation as to how to do the problem

The rate of reaction indicates the speed at which the reaction can occur. It can be expressed in terms of a change in the concentration of reactants or products per unit of time:

rate = concentration changetime change

The rate of reaction can be defined either as a decrease in the concentration of a reactant per unit of time or as an increase in the concentration of a product per unit of time.

Select the image to explore the activity that shows the different ways in which the rate of a reaction can be expressed.

When you click on the "Disappearance of reactants," "Appearance of products," or "Rate law expression" button, you will observe different expressions for the rate of the reaction.

Consider the following reaction:

2A+3Bâ3C+2D

Use the following data to determine the rate of reaction in terms of the disappearance of reactant A at time = 20 s.

Time (s)	0	20	40
[A](M)	0.1200	0.0720	0.0540

Express your answer in molar concentration per second to three significant figures.

Part B

Consider the following reaction:

2A+3Bâ3C+2D

Use the following data to determine the rate of reaction in terms of the appearance of product C when the time is 20 s.

Time (s)	0	20	40
[C](M)	0.000	0.0720	0.1440

Show transcribed image text

To understand how to use integrated rate laws to solve for concentration.

A car starts at mile marker 145 on a highway and drives at 55 mi/hr in the direction of decreasing marker numbers. What mile marker will the car reach after 2 hours?

This problem can easily be solved by calculating how far the car travels and subtracting that distance from the starting marker of 145.

55 mi/hrÃ2 hr=110 miles traveled

milemarker 145â110 miles=milemarker 35

If we were to write a formula for this calculation, we might express it as follows:

milemarker=milemarker0â(speedÃtime)

where milemarker is the current milemarker and milemarker0 is the initial milemarker.

Similarly, the integrated rate law for a zero-order reaction is expressed as follows:

[A]=[A]0ârateÃtime

[A]=[A]0âkt

since

rate=k[A]0=k

A zero-order reaction (Figure 1) proceeds uniformly over time. In other words, the rate does not change as the reactant concentration changes. In contrast, first-order reaction rates (Figure 2) do change over time as the reactant concentration changes.

Because the rate of a first-order reaction is nonuniform, its integrated rate law is slightly more complicated than that of a zero-order reaction.

The integrated rate law for a first-order reaction is expressed as follows:

[A]=[A]0eâkt

where k is the rate constant for this reaction.

The integrated rate law for a second-order reaction is expressed as follows:

1[A]=kt+1[A0]

where k is the rate constant for this reaction.

PART A

The rate constant for a certain reaction is k = 3.50Ã10^â3 sâ1 . If the initial reactant concentration was 0.400 M, what will the concentration be after 5.00 minutes?

Express your answer with the appropriate units.

PART B

A zero-order reaction has a constant rate of 5.00Ã10^â4M/s. If after 75.0 seconds the concentration has dropped to 2.50Ã10^â2M, what was the initial concentration?

Express your answer with the appropriate units.

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CHEM 204 Lecture Notes - Lecture 5: Molecularity, Second Order (Religious), Rate-Determining Step

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