Question:

What is the formula for zero order reaction?

Updated On: Apr 14, 2025

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Solution and Explanation

Concept:
In chemical kinetics, a zero-order reaction is one in which the rate of the reaction is independent of the concentration of the reactant(s). That means even if the concentration of the reactant changes, the reaction rate remains constant.

Integrated Rate Law for Zero-Order Reaction:
The formula is:
[A] = [A]₀ − kt

Where:
• [A] is the concentration of reactant A at time t
• [A]₀ is the initial concentration of reactant A
• k is the rate constant (with units mol·L⁻¹·s⁻¹ for zero-order)
• t is the time elapsed

Explanation:
Since the reaction is zero order, the rate of reaction = k, which is constant. Integrating this with respect to time gives a straight-line equation. This is similar to the slope-intercept form of a straight line (y = mx + c), where [A] decreases linearly with time.

Graphically, if you plot [A] vs. time (t), you'll get a straight line with a negative slope equal to −k and y-intercept equal to [A]₀. When [A] reaches zero, the reaction stops because the reactant is fully consumed.

Real-life Applications:
Zero-order kinetics are observed in some enzymatic reactions when the enzyme is saturated, and also in the decomposition of gases on metal surfaces like platinum or gold.

Conclusion:
The integrated rate law for a zero-order reaction is:
[A] = [A]₀ − kt
This equation is essential in understanding reaction mechanisms and predicting how concentration changes over time.

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Sl. No.	[A] (mol L⁻¹)	[B] (mol L⁻¹)	Initial rate (mol L⁻¹ s⁻¹)
1	0.1	0.1	0.05
2	0.2	0.1	0.10
3	0.1	0.2	0.05

Sl. No.	[A] (mol L^-1)	[B] (mol L^-1)	Initial rate (mol L^-1 s^-1)
1	0.1	0.1	0.05
2	0.2	0.1	0.10
3	0.1	0.2	0.05

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Concepts Used:

Chemical Kinetics

Chemical kinetics is the description of the rate of a chemical reaction. This is the rate at which the reactants are transformed into products. This may take place by abiotic or by biological systems, such as microbial metabolism.

Rate of a Chemical Reaction:

The speed of a reaction or the rate of a reaction can be defined as the change in concentration of a reactant or product in unit time. To be more specific, it can be expressed in terms of: (i) the rate of decrease in the concentration of any one of the reactants, or (ii) the rate of increase in concentration of any one of the products. Consider a hypothetical reaction, assuming that the volume of the system remains constant. R → P

Read More: Chemical Kinetics MCQ

Factors Affecting The Reaction Rate:

The concentration of Reactants - According to collision theory, which is discussed later, reactant molecules collide with each other to form products.
Nature of the Reactants - The reaction rate also depends on the types of substances that are reacting.
Physical State of Reactants - The physical state of a reactant whether it is solid, liquid, or gas can greatly affect the rate of change.
Surface Area of Reactants - When two or more reactants are in the same phase of fluid, their particles collide more often than when either or both are in the solid phase or when they are in a heterogeneous mixture. In a heterogeneous medium, the collision between the particles occurs at an interface between phases. Compared to the homogeneous case, the number of collisions between reactants per unit time is significantly reduced, and so is the reaction rate.
Temperature - If the temperature is increased, the number of collisions between reactant molecules per second. Increases, thereby increasing the rate of the reaction.
Effect Of Solvent - The nature of the solvent also depends on the reaction rate of the solute particles.
Catalyst - Catalysts alter the rate of the reaction by changing the reaction mechanism.