Final answer:
The concentration of the substance after seven half-lives would be approximately 0.04534 M.
Step-by-step explanation:
Given that the substance has a concentration of 5.80 M when the reaction begins and we want to find the concentration after seven half-lives, we can use the formula for the amount of reactant remaining after n half-lives of a first-order reaction, which is (1/2)n times the initial concentration.
So, if we substitute n = 7, the concentration after seven half-lives would be (1/2)7 times the initial concentration.
Converting it to decimal form, (1/2)7 = 0.0078125. Multiplying this by the initial concentration of 5.80 M, we get a concentration of approximately 0.04534 M after seven half-lives.