Mastering Chemistry Any help is appreciated. If you know the answer please give units :) Part A: The reactant concentration in a zero-order reaction was 5.00×10^?2M after 140s and 3.00×10^?2M after 300s. What is the rate constant for this reaction? -> For this I got that 1.25x10^-4M/s, which was labeled right. Part B: What was the initial reactant concentration for the reaction described in Part A? -> The hint given is: Use the integrated rate law for zero-order reactions to solve for [A]_0. Values for [A] and t are given in Part A, and your answer to Part A was the value of k. Part C: The reactant concentration in a first-order reaction was 6.10×10^?2M after 20.0s and 2.00×10^?3 after 95.0s. What is the rate constant for this reaction? Part D: The reactant concentration in a second-order reaction was 0.650M after 215s and 5.70×10^?2M after 900s. What is the rate constant for this reaction?