CHEM 142 Lecture Notes - Lecture 9: Reaction Rate Constant, Penicillin, Stoichiometry

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7 Jul 2016

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Rate is the change in a measurement over a period of time. In chemistry, we define the rate of a chemical reaction as a change in concentration (in molarity) over time (s). Use the concentration v. time graph for the decomposition of no2 to no and o2 to answer the following questions. 0-50 (0. 008 m-0. 01 m)/ (50s-0s) = -4. 0 10-5 m/s. 150-200 (0. 0048 m-0. 0055 m)/ (200s-150s) = -1. 4 10-5 m/s. 1 originally written by dr. harris, 2016: we can determine the instantaneous rate of change for [no2] at a given point based on the slope of the tangent line at that point. Estimate the rate of change of [no2] when [no2] = 0. 008 m and. 0. 008m (0. 0068-0. 0088)/(80-20) = -3. 3 10-5 m/s. As the concentration of the reactant no2 decreases the rate of the reaction decreases: use the stoichiometry of the reaction to determine the average rate of change for [o2] and [no] from.

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

A student studies the kinetics of reaction 1 below using a clock reaction technique, reaction 2, and the procedures given in this experiment. For reaction mixture 1, he measures a time to color change of 121 seconds and for reaction mixture 2, he measures a time of 58 seconds. The temperatures of the reaction mixtures were the same for both experiments.

6Iâ (aq)+ BrO3â (aq) + 6H+(aq) --> 3I2 (aq) + Brâ (aq) + 3H2O(l) (Reaction1,slow)

I2 (aq) + 2 S2O32â (aq) --> 2 Iâ (aq) + S4O62â (aq) (Reaction 2, fast)

a. Determine the change in concentration of S2O32â that occurred during the time period measured. This should be the same for both the reaction mixtures. First, use M1V1=M2V2 to determine the initial concentration of the S2O32â after mixing the contents of the two flasks but before the reaction begins. Next, find the final concentration of S2O32â by remembering that all the S2O32â is consumed when the color change occurs. You can then find the change in the concentration of S2O32â.

[S2O32â]0 =

â[S2O32â] =

b. Use the stoichiometry of Reactions 1 and 2 to determine the change in concentration of BrO3â during

the same time period. â[BrO3â] =

c. Calculate the initial rate for each reaction mixture. Recall that Rate = â â[BrOâ ] / ât

Rate for mixture 1:

Rate for mixture 2:

d. Method of Initial Rates

Complete the table below using M1V1=M2V2 to find the initial concentration of each reactant after mixing the contents of flasks I and II for both reaction mixtures. Enter the initial rates computed above.

Rxn Mixture [Iâ]0(M) [BrO3â]0(M) [H+]0 (M) Rate (M/s)

Use the method of initial rates and the relevant data above to determine the order of reaction 1 with respect to the concentration of iodide ions.

Order with respect to [Iâ]:_________________________

e. It is critical for the success of this experiment that the concentrations of the reactants Iâ, BrO3â, and H+ do not change significantly over the time period measured.

Why is this important?

f. By what percent did the bromate ion concentration change during the time period considered for mixture 1 in this experiment?

PercentChange = (|â[BrO3â ]| / [BrO3â ]0 ) x 100%

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 142 Lecture Notes - Lecture 9: Reaction Rate Constant, Penicillin, Stoichiometry

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