The slope of the linear plots for zero-order and first-order kinetics is typically:

• A. positive
• B. undefined
• C. negative
• D. zero

Answer: (C)

In zero- and first-order kinetics, the quantities you plot against time show a straight decline because the reactant is being consumed. For a zero-order reaction, the integrated rate law is [A] = [A]0 − k t, so the line you get by plotting [A] versus time has a slope of −k. For a first-order reaction, plotting the natural log of the concentration, ln[A], versus time gives ln[A] = ln[A]0 − k t, which is also a straight line with slope −k. Since k is defined as a positive constant, the slope must be negative in both cases. A positive slope would imply the concentration increases over time, which doesn’t describe the decay in these kinetics. An undefined or zero slope wouldn’t match the typical decay behavior either. So the slope is negative.