Question

For a zero-order reaction, $A\to B$, a graph of rate vs time has slope equal to: (where $k=rate$)
(A) $k$
(B) $-k$
(C) zero
(D) $-2.303k$

Answer 1

Hint: The graph between rate of reaction and time of a zero-order reaction can be obtained by comparing the integral form of zero-order reaction with the general form equation of the straight line. In these reactions, the rate is proportional to the zeroth power of concentration.

Complete step by step answer:
First, discuss zero-order reactions. Zero-order reactions are those chemical reactions wherein the rate does not vary with the increase or decrease in the concentration of the reactants. That’s why, the rate of these reactions is always equal to the rate constant of reactions.
The rate constant is the proportionality constant which is used to describe the relationship between the molar concentration of the reactants and the rate of a chemical reaction. The rate constant is denoted by $k$ and is also known as reaction rate constant for reaction rate coefficient.
The integral form of zero-order reaction can be written as:
$[A]=[A_0]-kt$
Here $[A]$ is the final concentration, $[A_0]$ is the initial concentration
 $k$ is called a rate constant, $t$ is the time.
When you plot a graph between time and rate you put time on the x-axis and the concentration on the y-axis. Now, when you compare this equation with the general equation of line i.e. $y=mx+c$
The slope you will get will be equal to $-k$. Hence, the slope of zero-order reaction is $-k$.
So, the correct answer is “Option B”.

Note:
Reaction rate or rate of reaction is the measure of how fast or slow a chemical reaction occurs in the conversion of a reactant into a product. For a first-order reaction, the rate is dependent on the concentration of a single species only. Iodization of acetone is an example of zero-order reaction.