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# Reaction Rate Chemistry!?

1)A reaction is said to be diffusion controlled when it occurs as fast as the reactants diffuse through the solution. The following is an example of a diffusion controlled reaction.

The rate constant for this reaction is 1.4x1011 M-1s-1 at 25oC and the reaction obeys the following rate law.

rate = k(H3O+)(OH-)

Calculate the rate of reaction in a neutral solution (pH=7.00).

Rate = ? M/sec

2)Calculate the rate at which N2O4 is formed in the following reaction at the moment in time when NO2 is being consumed at a rate of 0.0683 M/s.

Rate of N2O4 formation = ?M/sec

3)Assume that the instantaneous rate of disappearance of the MnO4- ion in the following reaction is 0.00413 M/s at some moment in time.

What is the rate of appearance of I2 at the same moment?

Rate of I2 appearance = ?M/sec

Help with either of these problems would be helpful! Thanks!

### 3 Answers

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At pH 7, [H3o+] = 10^-7 = [OH-]

rate = 1.4x10^11 * 10^-7 * 10^-7 = 1.4x10^-3 M s^-1

2 NO2 --> N2O4, so N2O4 is formed at half the rate NO2 is consumed

rate = 0.0342 M/s

assuming the MnO4- goes to Mn2+ and the I2 came from I-, then the I2 is formed at 5/2 the rate of MnO4- disappearance

rate = 0.0103 M/s

• Alright I'm not going to solve it for you but i'm going to explain it.

1) For the first question it's fairly easy. Since the rate=k(H30+)(OH-) and the pH of the solution is 7, that means the concentrations of H30+ and OH- are equal to 1x10-7. And they give you k so it's all a matter of just plugging in numbers. (remember, ph=-log(H30+)

For 2 and 3 , it's up to you to create the equations by using the words that expresses the reactions. REMEMBER, you must balance the equations with integers!! Once you know the ratio of the product to reactant you can plug that in and findi the rate constant for the opposite reactions.

• (i) Rate = 1.5 x 0.3 x 0.2 = 0.09 (ii) A = 0.025 / 0.029 x 0.78 = 1.105 (iii) k = 0.033 / 0.450 x 0.520 = 0.141 i'm guessing all three values are from different reactions. Hope i helped ^^

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