In this paper, the core theory of chemical reaction kinetics is systematically expounded, covering the basic concepts of reaction rate, reaction order and rate equation, and the influence of temperature on reaction rate is discussed. At the same time, the principles and applications of experimental methods such as temperature method, concentration method and spectroscopy method are introduced, which provides a practical reference for researchers to select appropriate experimental techniques.
Determination of hydrogen peroxide decomposition reaction rate constant and half-life
principle
Hydrogen peroxide decomposition reaction mechanism – Hydrogen peroxide is converted into water and oxygen during the decomposition process. The reaction can be carried out under the action of different catalysts, such as manganese dioxide (MnO₂) and potassium iodide (KI), which speed up the reaction.
Reaction rate constant vs. half-life: The rate constant indicates how fast or slow the reaction speed is, while the half-life is the time it takes for the reactant concentration to decrease to half. The role of the catalyst is to accelerate the reaction, which affects the rate constant and half-life.
Instruments & Reagents
instrument
Reaction vessels (e.g. flasks with stirring devices), gas collection devices, Spectrophotometer s (to monitor the reaction progress), temperature control devices, timers.
reagent
Hydrogen peroxide solution, catalyst (e.g., MnO₂, KI), distilled water, acid or alkali solution (adjust pH).
Experimental Procedure
Check the tightness of the reaction system before the start of the experiment to ensure that there are no gas leaks.
Prepare the appropriate concentration of hydrogen peroxide solution and catalyst and add it to the reaction vessel.
Start the timer and record the time of the start of the reaction, making sure that the reaction vessel is well sealed.
Periodic sampling is taken, and the volume of the reaction gas or the concentration of hydrogen peroxide is measured using a Spectrophotometer or other method.
Concentration or volume data were recorded at each time point.
data processing
Record the concentration or gas volume data at each time point during the experiment, and plot graphs to show the change trend.
Solution:
Calculate the rate constant – determine the rate constant by plotting the concentration over time.
Determine the half-life – Calculate the half-life using the rate constant, which is the time it takes for the reactant concentration to be reduced to half.
Catalyst Effect – Compare reaction rate constants with and without catalysts to assess the effect of catalysts on reaction speeds.
Determination of sucrose conversion reaction rate constant, reaction order and half-life (polarimetry)
principle
The optical rotation changes in the sucrose conversion reaction, and the sucrose is converted to glucose and fructose under acid catalysis, and the optical rotation changes during the reaction. The reaction process can be tracked by monitoring the change in optical rotation.
Specific rotation is the ratio of optical rotation to solution concentration and optical path length to help determine the change in concentration of sucrose and thus calculate the reaction rate constant and half-life.
Instruments & Reagents
instrument
Polarimeters and their accessories (e.g. cuvettes), temperature controls (e.g. thermostatic Water Baths).
reagent
Sucrose solution, acid catalyst (e.g., hydrochloric acid), distilled water.
Experimental Procedure
A sucrose solution of a certain concentration was prepared, and an acid catalyst was added. Place the sample in the polarimeter and adjust to the appropriate pathlength.
Samples are taken at regular intervals and optical rotation is measured. Optical rotation data were recorded at each time point.
Precautions
Ensure that the polarimeter is calibrated accurately and that the sample is kept at a constant temperature during the measurement to avoid air bubbles affecting the reading.
Data analysis and processing
Calculate the rate constant – plot the reaction progress based on the change in optical rotation, and use the experimental data to determine the rate constant.
Reaction order – Analyze the reaction order by specific rotation data.
Half-life – The half-life of the reaction is calculated from the rate constant, i.e., the time it takes for the sucrose concentration to be reduced to half.
Determination of Ethyl Acetate Saponification Reaction Order, Rate Constant, and Activation Energy (Conductivity Method)
principle
Conductance change in ethyl acetate saponification reaction: Ethyl acetate reacts with sodium hydroxide to produce sodium acetate and ethanol, and the sodium acetate produced in the process results in an increase in the conductivity of the solution. The change in conductivity reflects the reaction progress and helps determine the reaction order, rate constant, and activation energy.
Instruments & Reagents
Conductivity meters and related equipment (e.g. conductivity cells).
Ethyl acetate, sodium hydroxide solution, distilled water.
Experimental Procedure
A certain concentration of ethyl acetate and sodium hydroxide solution is configured to ensure that the reaction system is uniform.
The reaction liquid is placed in a conductivity cell and the conductivity is measured periodically using a conductivity meter. Conductivity data was recorded at different time points.
Precautions
Ensure that the conductivity meter is accurately calibrated, and the reaction system is kept at a constant temperature during the measurement process to avoid air entering the sample and affecting the results.
data processing
The reaction progress is plotted according to the change in conductivity over time, and the rate constant and reaction order are obtained by fitting the data.
The activation energy is calculated from conductivity data at different temperatures, usually using the Arrhenius equation.
Determination of cyclopentene decomposition reaction order, rate constant, and activation energy (thermal decomposition method)
principle
Cyclopentene is decomposed under heating conditions to form gas products, and gas chromatography is used to analyze the concentration changes of the decomposition products, so as to determine the reaction order, rate constant and activation energy.
Instruments & Reagents
Gas chromatographs, heating devices (e.g. furnaces), cooling devices.
Cyclopentene gas, inert gas (e.g. nitrogen).
Experimental Procedure
Set the temperature program of the heating unit.
Cyclopentene gas is injected into the reaction system and monitored in real time by gas chromatograph.
Gas composition and concentration data were recorded at different time points.
The reaction is carried out at a set temperature, and the reaction gas is sampled at regular intervals for analysis.
data processing
Detailed documentation of the concentration of each component in the gas chromatogram as a function of time.
The reaction order and rate constant were calculated by fitting the concentration-time curve, and the activation energy was calculated using the Arrhenius equation using the data at different temperatures.
Determination of the reaction rate of ammonium perdisulfite oxidation of potassium iodide
Experiment configuration and procedure
Prepare a solution of ammonium perdisulfate and potassium iodide at a certain concentration.
In the reaction vessel, the ammonium perdisulfite solution is mixed with the potassium iodide solution in the set ratio.
The amount of iodine produced during the reaction is determined using a titration method such as sodium thiosulfate titration.
Experimental manipulation
Samples were taken and titrated at set intervals, recording the volume of sodium thiosulfate required for each titration.
data processing
Record the sodium thiosulfate consumption at the time of each sampling, as well as the corresponding time.
According to the titration results, the reaction rate constant was calculated, the reaction process diagram was drawn, and the variation of the reaction rate with time was analyzed.
In conclusion, this article introduces in detail the basic concepts of chemical reaction kinetics, including reaction rate, reaction order, rate equation, and the effect of temperature on reaction rate. In addition, the principles, advantages and disadvantages of commonly used experimental methods such as temperature method, concentration method and spectroscopy method are discussed. By comparing these methods, the article helps the reader to choose the appropriate experimental technique.
