Question

Which of the following graphs most appropriately represents a zero-order reaction?

• A.
• B.
• C.
• D.

Hint:

For zero-order reactions, the concentration decreases linearly with time, and the rate is constant over the course of the reaction.

Answer 1

The Correct Option is B

To solve this problem, we need to understand the characteristics of a zero-order chemical reaction. In a zero-order reaction, the rate of reaction is constant and independent of the concentration of the reactants.

The rate equation for a zero-order reaction can be expressed as: 

\[\text{Rate} = k\]

where \(k\) is the rate constant.

The integrated rate law for a zero-order reaction is given by:

\[[A] = [A]_0 - kt\]

where \([A]\) is the concentration of the reactant at time \(t\), \([A]_0\) is the initial concentration, \(k\) is the rate constant, and \(t\) is the time elapsed.

This equation resembles the equation of a straight line:

\[y = mx + c\]

In this context, the concentration \([A]\) acts as \(y\), time \(t\) as \(x\), \(-k\) as the slope \(m\), and \([A]_0\) as the intercept \(c\).

Therefore, for a zero-order reaction, a plot of \([A]\) vs. \(t\) will be a straight line with a negative slope. Given the options, the correct graph that represents a zero-order reaction is:

This graph clearly shows a linear decrease in concentration over time, indicating a zero-order reaction.

Let's summarize why other options are incorrect:

• Other graphs would represent different order reactions (like first or second order) typically showing a nonlinear relationship between the concentration and time.

Answer 2

For a zero-order reaction, the rate law is: \[ \text{Rate} = k, \] which means the rate is independent of the reactant concentration. The integrated rate law for a zero-order reaction is: \[ [\text{A}] = [\text{A}]_0 - kt. \] This shows that the concentration of the reactant decreases linearly with time. Therefore, the graph of concentration versus time for a zero-order reaction is a straight line with a negative slope.