29. We must bear in mind that the absorbance is directly proportional to the concentration. If the absorbance is reduced by half this means that the concentration presented a reduction of 50% as well. Now, we have an initial absorbance, t=0. This will be when the reactant, C25H30N3, concentration is 100%.
The absorbance value for a 100% initial amount is 0.62, with a rule of three we can find the absorbance that we would have if 75% reacts.
The absorbance shows us the amount of C25H30N3 that remains, that is, the amount that does not react. This value will be equal to:
100%-75%=25%
Now, with a rule of three, we calculate the absorbance that the solution should have by 25% of C25H30N3 compared to the initial concentration.
[tex]Absorbance=\frac{0.65\times25\%}{100\%}=0.15[/tex]
Now, if we see the data obtained, the time in which this absorbance is obtained is 300 seconds.
So, for question 29 the answer will be: (C) 300 s
30. Now, we are told that the first-order reaction with respect to C25H30N3+ is first order. This means that the rate of the reaction is directly proportional to the concentration. If the C25H30N3+ solution is diluted, the concentration will also decrease. Therefore, the reaction rate will be lower.
For question 30 the answer will be: (B) It will be lower
