# Chemical Kinetics

# Chemical Kinetics

**This lesson aligns with NGSS PS1.B**

**Introduction**

Chemical kinetics holds significant importance with insights into various aspects of chemical reactions. Specifically, the term 'kinetics' deals with the rate of change of a given quantity. To illustrate, the rate of change of displacement is denoted as velocity, and similarly, acceleration represents the rate of change of velocity. Chemical kinetics focuses on unravelling the dynamic processes governing the rates and mechanisms of chemical transformations. In this article, we will explore the core concepts of chemical kinetics, shedding light on its significance and applications in the world of science and industry.

**Defining Chemical Kinetics:**

Chemical kinetics, also known as reaction kinetics, provides valuable insights into the rates of reactions—the speed at which reactants are converted into products as well as the factors influencing them.

Typically, chemical reactions are categorized into different speed classes based on their rates. For instance, reactions such as Na + [math]H_2O[/math] are considered fast, those like Mg + [math]H_2O[/math] fall into the moderate category, and reactions involving esterification are classified as slow.

**Rate of Formations and Disappearances**

In any chemical reaction, the quantity of reactants decreases, whereas the amount of products increases. It's crucial to recognize that the overall rate of the reaction depends on the rate at which reactants are consumed or the rate at which the products are formed.

By graphing the concentration of reactants and products against time, one can readily compute the rates of product formation and reactant disappearance by assessing the slopes of the respective curves. It's noteworthy that the overall rate of the reaction may or may not align with the rates of formations and disappearances.

At time t=0, product concentration is zero. Examining the graph reveals that the slope of the reactants curve is negative, while that of the products curve is positive. This signifies a decrease in the concentration of reactants and an increase in the concentration of products. To illustrate the interconnectedness of the overall reaction rate, the rate of reactant disappearance, and the rate of product formation.

Let's consider a straightforward example – the formation of water.

2[math]H_2[/math] + [math]O_2[/math] → 2[math]H_2O[/math]

From this equation, it is evident that for every mole of [math]O_2[/math] consumed, two moles of [math]H_2[/math] will also be consumed, resulting in the formation of two moles of [math]H_2O[/math]. Assuming the reaction proceeds for 10 minutes with an initial mixture of 1 mole each of [math]H_2[/math] and [math]O_2[/math], we can track the changes in moles over time.

t = 0 1 1 0

t = 10 mins 1 – 0.5 1 – 0.25 0.5

Say after 10 minutes, 0.5 moles of [math]H_2[/math] is consumed, and according to stoichiometry, 0.25 moles of [math]O_2[/math] is consumed, and 0.5 moles of [math]H_2O[/math] is formed. Now, let us calculate the rates for [math]H_2[/math], [math]O_2[/math] and [math]H_2O[/math] for the first 10 minutes.

**Rate of disappearance of [math]H_2[/math]**

**Rate of Disappearance of [math]O_2[/math]**

**Rate of Formation of [math]H_2O[/math]**

Based on the above calculations, it is evident that the rate at which [math]H_2[/math] is consumed is twice the rate at which [math]O_2[/math] is consumed. This observation underscores the connection between the stoichiometry of the reaction and the rates of formation and disappearance of various reactants and products, establishing the following relationship.

Let,

aA + bB → cC + dD

be a reaction.

Where r → rate of the overall reaction,

Δ[A], Δ[B], Δ[C], and Δ[D] demonstrate a change in concentration and

st → change in time.

Therefore,

**Significance of Reaction Rates:**

The reaction rate measures how quickly reactants transform into products during a chemical reaction. It quantifies the change in concentration of either the reactants consumed or the products formed per unit of time. Essentially, reaction rate reveals the speed at which molecular collisions lead to the formation of new substances. This crucial parameter is influenced by factors such as concentration, temperature, and catalysts.

**Summary**

- Chemical Kinetics specifically, the term 'kinetics' deals with the rate of change of a given quantity.
- In any chemical reaction, the quantity of reactants decreases, whereas the amount of products increases.
- The reaction rate measures how quickly reactants transform into products during a chemical reaction.
- It quantifies the change in concentration of either the reactants consumed or the products formed per unit of time.

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