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Reaction Mechanisms

Reaction Mechanisms

Chemical reactions often occur in a stepwise fashion, involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs.
For instance, the decomposition of ozone appears to follow a mechanism with two steps:

Determining Order of Reaction

Determining Order of Reaction

Rate laws describe the relationship between the rate of a chemical reaction and the concentration of its reactants. In a rate law, the rate constant k and the reaction orders are determined experimentally by observing how the rate of reaction changes as the concentrations of the reactants are changed. A common experimental approach to the determination of rate laws is the method of initial rates. This method involves measuring reaction rates for multiple experimental trials carried out using...

Reaction Rate

Reaction Rate

The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time dependence of some property that can be related to reactant or product amounts. Rates of reactions that consume or produce gaseous substances, for example, are conveniently determined by measuring changes in volume or pressure.
The mathematical representation of the change in the concentration of reactants and products, over time, is the rate...

Reaction Quotient

Reaction Quotient

The status of a reversible reaction is conveniently assessed by evaluating its reaction quotient (Q). For a reversible reaction described by m A + n B ⇌ x C + y D, the reaction quotient is derived directly from the stoichiometry of the balanced equation as

Reaction Yield

Reaction Yield

The theoretical yield of a reaction is the amount of product estimated to form based on the stoichiometry of the balanced chemical equation. The theoretical yield assumes the complete conversion of the limiting reactant into the desired product. The amount of product that is obtained by performing the reaction is called the actual yield, and it may be less than or (very rarely) equal to the theoretical yield.

Half-life of a Reaction

Half-life of a Reaction

The half-life of a reaction (t1/2) is the time required for one-half of a given amount of reactant to be consumed. In each succeeding half-life, half of the remaining concentration of the reactant is consumed. For example, during the decomposition of hydrogen peroxide, during the first half-life (from 0.00 hours to 6.00 hours), the concentration of H2O2 decreases from 1.000 M to 0.500 M. During the second half-life (from 6.00 hours to 12.00 hours), the concentration decreases from 0.500 M to...

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Related Experiment Video

Updated: Jan 27, 2026

Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions

Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions

Published on: April 4, 2014

Characterization of Enzymatic Reactions Using ITC.

Barbara Zambelli¹

¹Laboratory of Bioinorganic Chemistry, Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy. barbara.zambelli@unibo.it.

Methods in Molecular Biology (Clifton, N.J.)

|April 1, 2019

Summary

This study details isothermal titration calorimetry (ITC) for measuring enzyme kinetics. It provides a protocol to quantify thermodynamic and kinetic parameters, aiding biological understanding and industrial enzyme applications.

Keywords:

Catalytic rate constant Enzymatic catalysis Isothermal titration calorimetry Michaelis constant Michaelis-Menten Reaction kinetics Thermodynamics

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Last Updated: Jan 27, 2026

Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions

Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions

Published on: April 4, 2014

Enzymatic Cascade Reactions for the Synthesis of Chiral Amino Alcohols from L-lysine

Enzymatic Cascade Reactions for the Synthesis of Chiral Amino Alcohols from L-lysine

Published on: February 16, 2018

Measuring In Vitro ATPase Activity for Enzymatic Characterization

Measuring In Vitro ATPase Activity for Enzymatic Characterization

Published on: August 23, 2016

Area of Science:

Biochemistry
Biophysical Chemistry
Enzymology

Background:

Enzyme activity is crucial for understanding biological processes and developing industrial applications.
Calorimetry, a technique measuring heat changes, is well-suited for probing biochemical transformations.
Characterizing enzyme kinetics provides essential thermodynamic and kinetic parameters.

Purpose of the Study:

To describe the experimental setup and data analysis for isothermal titration calorimetry (ITC) in enzyme catalysis.
To provide a protocol for quantifying thermodynamic (ΔH) and kinetic (K_M, k_cat) parameters of enzyme reactions.
To offer guidelines for selecting appropriate procedures and optimizing experimental conditions for reliable data acquisition.

Main Methods:

Utilizing isothermal titration calorimetry (ITC) to measure heat changes associated with enzyme-catalyzed reactions.
Implementing a detailed protocol for experimental setup and raw data acquisition.
Applying specific data analysis methods to derive kinetic and thermodynamic parameters from ITC curves.

Main Results:

Quantification of thermodynamic parameter ΔH (enthalpy change).
Determination of kinetic parameters K_M (Michaelis constant) and k_cat (turnover number).
Establishment of a reliable method for analyzing enzyme kinetics using ITC.

Conclusions:

Isothermal titration calorimetry (ITC) is an effective method for characterizing enzyme kinetics.
The described protocol facilitates the accurate determination of key thermodynamic and kinetic parameters.
This approach supports advancements in both fundamental biological research and industrial enzyme technology.