A first order reaction takes 69.3 minutes for 50% completion. Time in ...
Calculation of Time to Complete 80% of Reaction
Given:
- First order reaction
- 50% completion time = 69.3 minutes
To find: Time to complete 80% of the reaction
Formula Used
For a first order reaction, the time taken for a given percentage of completion can be calculated using the following formula:
t = (0.693/k) x log10 (A0/A)
where:
- t = time taken for percentage completion
- k = rate constant
- A0 = initial concentration of reactant
- A = concentration of reactant at time t
Calculation
Let's first calculate the rate constant (k) using the given information:
t1/2 = 69.3 minutes (given)
Using the formula:
t1/2 = (0.693/k)
k = 0.693/t1/2 = 0.693/69.3 = 0.01 min-1
Now, let's use the formula to calculate the time taken for 80% completion:
t = (0.693/k) x log10 (A0/A)
Let's assume the initial concentration of reactant (A0) is 1. Therefore, the concentration of reactant at 50% completion (A) would be 0.5.
Using the formula:
t = (0.693/0.01) x log10 (1/0.5)
t = 46.1 minutes
Answer
The time taken to complete 80% of the reaction is 46.1 minutes.
Explanation
Given that the reaction is a first order reaction, we can use the formula to calculate the time taken for a given percentage of completion. In this case, we were given the time taken for 50% completion and we used this information to calculate the rate constant (k). Once we had the value of k, we used the formula again to calculate the time taken for 80% completion. We assumed an initial concentration of 1 for simplicity. The final answer was 46.1 minutes.