CHEM 1A03 Study Guide - Midterm Guide: Chemical Kinetics, Jakarta, Reaction Intermediate

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CHEM 1A03 Full Course Notes

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T is measured in s r is measured in mol/(l s) When the amount of reactant is being considered, it is referred to as the rate of consumption. [even though the value will have a negative sign when determined mathematically, the absolute value is used and it is referred to as the rate of consumption. ] When the amount of product is being considered, it is referred to as the rate of production. The rate of reaction is often found through graphical analysis of kinetics data. C at start of reaction, high concentration of reactants and high rate of reaction (fast) near end of reaction, low concentration of reactants and low rate of reaction (slow) At the beginning of reactions, when the concentration of reactant is highest, there are more product- forming collisions occurring and the consumption of reactants will be greater. The graph has a steep slope indicating a large rate of change in concentration; a high rate of reaction.

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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%

A student studying the decomposition of hydrogen peroxide noticed that the rate at which oxygen gas collected was noticably slower after the reaction had been running for several minutes than it was when the reaction was first started. Select the best answer from the list of statements. The lower rate of oxygen collection is likely due to an error in making the measurement. There is no reason for the rate to be different than it was at the beginning of the reaction. After the reaction has been running for several minutes the concentration of hydrogen peroxide will be lower because it is being decomposed. This lower concentration is the reason the rate of oxygen production is slower. The lower rate of oxygen collection is likely due to a change in atmospheric pressure during the experiment. Oxygen is a gas and the volume of a gas depends on atmospheric pressure. After the reaction has been running for several minutes the concentration of the catalyst will be lower because it is being used up. This lower concentration is the reason the rate of oxygen production is slower. Match the chemical with the statement that best describes the observed change in the rate of the reaction when the concentration of that chemical was changed. the H_2O_2 concentration is doubled the rate of oxygen collected is approximately half as fast the KCl concentration is doubled the rate of oxygen collected is approximately four times faster the Kl concentration is doubled the rate of oxygen collected is approximately twice as fast the Fecl_3 concentration is doubled the rate of oxygen collected is approximately four times slower there is little or no effect on the rate of oxygen collection Select the statement that describes the relationship between the rate of a reaction and the length of time needed to produce a given quantity of a product of the reaction. The time required to produce a given quantity of a product is directly proportional to the rate of the reaction. For a reaction that runs twice as fast, the given quantity of product will be produced in twice the time. The time required to produce a given quantity of a product is inversely proportional to the rate of the reaction. For a reaction that runs twice as fast, the given quantity of product will be produced in half the time. There is a relationship between the rate of a reaction and the time required to produce a given quantity of a product. It is not possible to know what that relationship is without running experiments. There is no relationship between the rate of the reaction and the time required to produce a given amount of product.

question d and 2 and part E 1 and 2

CHEM 1A03 Study Guide - Midterm Guide: Chemical Kinetics, Jakarta, Reaction Intermediate

CHEM 1A03 Full Course Notes

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