Reaction kinetics is the study of reaction rates and their effects. Many factors, such as concentration, pressure, temperature, and enzyme activity can affect the rate of a reaction.
The speed of a chemical reaction is also an important factor called the reaction rate. Reaction rates vary dramatically; some reactions take seconds, while others take thousands of years. Several factors can affect the rate of a reaction, and the study of the interactions between these factors and the rate of chemical reactions is called reaction kinetics.
As you read, here are some of the questions you'll find answers to:
How can high school students learn the concept of chemical interactions with each other?
How can teachers explain the importance of reaction kinetics from a practical perspective?
What are the advantages of a virtual laboratory?
There are three reasons why reaction kinetics can be difficult for even the most active students.
Reaction kinetics occurs at the molecular level. You cannot see or feel them. Not being able to picture the process and not seeing its applicability to the real world can frustrate learning and make it difficult for students to stay motivated.
The rate of a reaction is the change in the concentration of the reactants or products per unit time.
Figure 1. A plot of the number of reactant (A) and product (B) molecules against time. The reactants decrease while the products increase over time.
Let's take the following reaction as an example:
The reaction rate can be determined by measuring the rate at which reactant A is lost.
[A2]: concentration of A at t2 (M)
[A1]: concentration of A at t1 (M)
t2: time 2(s)
t1: time 1(s)
The unit of reaction rate is (mol/L)/s or M/s.
The rate of the reaction is not constant but changes over time. This is because changes in concentration and concentration affect the rate of the reaction.
Figure 2. The reaction rate can be determined by changes in the concentration of H2O2 over time. The instantaneous rate at 12 o'clock can be obtained by calculating the slope of the tangent to the curve at that time. The initial velocity is the instantaneous velocity at t = 0.
Points to note:
The average rate of reaction: change in concentration of products or reactants divided by the time interval under consideration.
Instantaneous rate: The speed of a reaction at a given point in time.
Initial rate: The instantaneous rate of reaction at "zero time", i.e. at the start of the reaction.
With a foundation laid about student challenges on this topic, here are five things you can incorporate into your reaction kinetics class to make it more engaging, accessible, and fun for you and your students.
Alexander Gorban and Jablonsky proposed that the history of chemical dynamics can be divided into three generations. The first was the Van 't Hoff wave, which sought general laws of chemical reactions and combined kinetics with thermodynamics. The second can be called the Semenov-Hinschelud wave, focusing on the mechanism of the reaction, in particular the chain reaction. The third relates to Aris and a detailed mathematical description of the network of chemical reactions.
Factors affecting the rate of reaction: The rate of a reaction can vary depending on many factors. The following are the most common ones we can use to influence the reaction rate:
1. Reagent Concentration
The rate of a reaction usually increases as the concentration of the reactants increases. Although the specific mechanisms for this are complex, they are still intuitive because there will be more reactive molecules to react with each other.
2. Temperature of reaction mixture
Increasing the temperature of the system usually speeds up chemical reactions. As the temperature increases, the reactant molecules move faster and with higher energy. As a result, they undergo reactions more frequently, thereby increasing the reaction rate.
Figure 3. This diagram shows the concept of why an increase in temperature increases the rate of a reaction. The proportion of reactive molecules is greater at higher temperatures.
3. Presence of catalyst
A catalyst is a substance that speeds up a reaction without undergoing a permanent chemical change. In the Arrhenius equation, this is defined as the decrease in the activation energy (Ea) of the reaction. Catalysts can also be seen naturally in biochemical reactions. These biological catalysts are called enzymes. Enzymes are large molecules, usually proteins, that bind to certain substrates and redirect them so they can react easily. As a result, the presence of enzymes speeds up reactions and biological processes.
4. Solvent in reaction
Solvents can affect the rate of a reaction through the physical properties and interactions of molecules with reactants and products. However, the choice of solvent depends on things other than just the rate of the reaction, such as the solubility of the reactants and products. It is important to choose a chemically suitable solvent and catalyst.
The collision model or collision theory is based on the kinetic-molecular theory. It attempts to explain the effect of concentration and temperature on the reaction rate. According to the model, reactant molecules only react when they collide with the right orientation and sufficient energy to overcome the activation energy. Increasing the percentage of successful collisions increases reaction speed.
Figure 5. For the reactants to collide successfully, two conditions must be met: 1) The energy of the collision must be equal to or greater than the activation energy. 2) The orientation must allow the formation of new chemical bonds.
A potential energy diagram shows the change in potential energy of a system when it undergoes a chemical reaction.
The activation energy (Ea) is the minimum energy required to start a reaction. The reaction rate is highly dependent on the activation energy. The lower the activation energy, the faster the reaction rate.
The enthalpy change for the reaction, ΔH, is estimated as the difference in “heat energy” between the reactants and products (at constant pressure).
The molecule at the top of the curve or energy barrier is called the activated complex or transition state.
Reactions that release heat are called exothermic. The enthalpy change ΔH for an exothermic reaction is negative. This may seem counterintuitive, but remember that system properties are viewed from a systems perspective. Since the system loses heat (by releasing it to the surroundings), the enthalpy change is negative. A negative ΔH value means that the enthalpy of the products is less than the enthalpy of the reactants.
The opposite is true for reactions that consume heat as they progress. Such a reaction is called endothermic. The enthalpy change ΔH for an endothermic reaction is positive because heat is added to the system. A positive ΔH value means that the enthalpy of the products is higher than the enthalpy of the reactants.
Note that If a chemical reaction is exothermic and takes place in one direction, it is endothermic and takes place in the opposite direction. The magnitude of the enthalpy change, ΔH, is the same but the number is reversed.
Hydrogen peroxide (H2O2) is a strong oxidizing agent and contains peroxide groups with oxygen-oxygen single bonds. The peroxide bond is unstable, leading to easy decomposition of the compound. Dilute hydrogen peroxide is colorless at room temperature.
Hydrogen peroxide can be used to treat a variety of inorganic and organic contaminants, as a bleaching agent in the paper and textile industry, and as a disinfectant. At high temperatures or in the presence of a catalyst, pure hydrogen peroxide decomposes into oxygen and water. If hydrogen peroxide's decomposition rate is fast enough, hydrogen peroxide can be utilized as a monopropellant for submarines and satellites.
A unique way to teach reaction kinetics is through virtual laboratory simulations. At Labster, we strive to provide highly interactive lab presentations using game-based elements such as storytelling and scoring systems in an immersive 3D world.
Discover Labster's reaction kinetics Simulation, which allows students to learn about reaction kinetics through active inquiry-based learning. In the simulation, students will learn the main factors that influence the rate of a chemical reaction and use this knowledge to improve the output of our drone transporter’s propulsion fuel.
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