Introduction
A reaction coordinate is a one-dimensional abstract coordinate used in chemistry to show progress along a reaction route. It’s frequently a geometric parameter that varies as more molecular entities are converted. A reaction coordinate is known as a collective variable in molecular dynamics simulations.
A reaction coordinate diagram is a graph that shows the relationship between energy and reaction progress. The activation energy, which is the point on the graph where the line is curving up, is the amount of energy that needs to be added.
Table of Contents
- Reactions and Energy
- Activation Energy
- Exothermic Versus Endothermic Reactions
- Positive and Negative Catalysts
- Frequently Asked Questions
Reactions and Energy
Thousands of responses are taking place all around you, thanks to the trees and plants. Some of these processes produce energy, while others consume it.
All reactions require energy from the simplest, such as boiling water to changing liquid water into gaseous water, to the most sophisticated, such as electrochemical processes. A reaction coordinate diagram can be used to see what happens to the energy in a reaction. A reaction coordinate diagram is a graph that shows the relationship between energy and reaction progress.
Explaining Reaction Coordinate Diagram
Let’s begin with the letter ‘A.’ This is a picture of the reactants before the reaction. Energy is contributed to the reaction as it occurs, and this energy is frequently in the form of heat. As a result, the line rises until it reaches a peak. The line then curves downward. In this case, the energy level of ‘B’ (the products) is lower than that of ‘A.’ 
The activation energy is the quantity of energy that had to be added. And the energy difference is known as delta E, which is the energy difference between the starting ingredients and the end product.
Activation Energy
In 1889, a Swedish physicist named Svante Arrhenius coined the term “activation energy.” In a reaction, the activation energy is crucial. If the activation energy is too high, the reaction will rarely (though ever) occur, even if the products have significantly lower energy than the reactants. Enzymes will be used in numerous processes to address this.
The smallest amount of additional energy required by a reactive molecule to transform into the product is the activation energy. It’s also known as the smallest amount of energy needed to activate or energise molecules or atoms for them to conduct a chemical reaction or transformation.
Further Reading:
Exothermic Versus Endothermic Reactions
Exothermic Reaction
A chemical process in which energy is released in the form of heat or light is known as an exothermic reaction. These reactions are the opposites of endothermic reactions, and they can be written as: Reactants → Products + Energy.
Hence, in an exothermic reaction, energy is transferred into the surroundings rather than absorbing energy from the surroundings as in an endothermic reaction. The change in enthalpy (â–³H) in an exothermic reaction will be negative.
The activation energy for Forward reaction (Ea)f
The activation energy for Forward reaction (Ea)b
(Ea)f < (Ea)b
(ROR)f > (ROR)b
â–³H = (Ea)f – (Ea)b
â–³H = -ve value
(Ea)f = â–³H, Only one can be possible for Exothermic Reaction
(Ea)f > â–³H
(Ea)f < â–³H
Further Reading:
Endothermic Reaction
Endothermic reactions are chemical processes in which the reactants take heat energy from the environment and create products. These reactions cause a cooling effect by lowering the temperature of their immediate surroundings. Ice cubes absorb heat energy from their surroundings and melt to generate liquid water, an example of an endothermic physical process (no chemical bonds are broken or formed).
(Ea)f > (Ea)b
(ROR)f < (ROR)b
â–³H = (Ea)b – (Ea)f
â–³H = +ve value
(Ea)f > â–³H (Always ) ………… universal
The product must be more disordered than the reactants for an endothermic reaction to occur. Another way to think of disorder is the ability for the molecules to have more freedom in motion.
Further Reading:
Positive and Negative Catalysts
A catalyst is a chemical compound that speeds up or slows down the rate of a chemical reaction. When it comes to the activation energy, a catalyst helps to lessen it. The energy of the initial reactants, on the other hand, remains unchanged. The activation energy is the only thing that a catalyst changes.
Depending on the necessity or demand of the chemical reaction, many types of catalysts might be used.
Positive Catalysts
Positive catalysts are those that speed up the rate of a chemical process. The reaction rate is boosted because the activation energy of such a catalyst is reduced by accepting a smaller route.
Negative Catalysts
Catalysts that slow down the reaction rate are negative catalysts (inhibitors). It slows down the reaction by raising the activation energy barrier, which reduces the amount of reactant molecules that can be converted into products, slowing down the reaction.
Further Reading:
Frequently Asked Questions on Reaction Coordinate Diagram
How many steps are involved in the reaction coordinate diagram?
The reaction is divided into two steps, the first of which is the slowest and the second of which is the fastest. Both of these processes are exothermic.
What is the difference between a Transition State and an Intermediate State?
An intermediate might be a volatile molecule (a reactive intermediate) or an unstable molecule (a non-reactive intermediate). The difference between an intermediate and a transition state is that an intermediate has a discontinuous duration (ranging from a few nanoseconds to many days). In contrast, a transition state only lasts for one bond vibration cycle.
What is the difference between energy and activation energy?
A form of energy is the activation energy. Energy measures a person’s ability to do labour, whereas activation energy is the amount of energy required to generate an activated complex during a chemical reaction.
Which is the highest point on a reaction coordinate diagram?
The saddle point represents the transition state, which is the highest energy point on the reaction coordinate connecting the reactant and product. A reaction coordinate diagram shows one or more transient intermediates as high-energy wells connected by a transition state peak.
Does catalyst affect enthalpy?
We might expect a catalyst to affect enthalpy because it affects activation energy, but it doesn’t. The chemical compositions of the reactants and products determine the change in enthalpy of a reaction; not the path travelled to get from one to the other.
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