Final answer:
To find the initial concentration of substance A in a chemical reaction from a given concentration at a certain time, we would need information about the reaction's kinetics. Without details on the rate of reaction, we cannot accurately determine the initial concentration.
Step-by-step explanation:
The question relates to determining the initial concentration of a substance, designated A, in a reaction A (aq) → B (aq). Here's how we can approach the problem: given that the concentration of A is 0.36 M at 28 seconds, we need to use chemical kinetics concepts to find the initial concentration. The information provided in the references suggests that the concentration decreases over time from an initial value (found from example problems like the 0.0200 M initial concentration of butadiene). The rate at which this concentration decreases is the change in concentration divided by time. If we are not given a specific reaction rate or more information about the reaction's kinetics, we cannot directly calculate the initial concentration without more data. However, in a typical reaction like A (aq) → B (aq), where concentration halves over a given time period, the initial concentration could theoretically be 2 times the given concentration after that period, assuming a first-order reaction with a constant half-life. Without additional context, exact determination of the initial concentration cannot be calculated.