Introduction

This chapter is all about how chemical changes take place within a state of a matter. Different examples in nature remind us of physical and chemical changes that things undergo. For example, grapes getting fermented, milk kept at room temperature in summer, food getting cooked, etc. How do these things happen? What is the reason behind it? This chapter on chemical reactions and equations explains it all. This can be explored by means of general observation of how substances change.

A chemical reaction takes place when there is either a change of temperature, state, or color or there is an evolution of some gas. These observations tell us that a chemical reaction has taken place. Let us move forward and explore even more.

Chemical Equations

When two substances react, they form a new product. There is a change of state of the reactants and they give a new product in the reaction.

The left side of the arrow displays the substances that react, combined by a (+) sign, while the right side displays the product that is formed. The arrow gives the direction of the reaction.

Formulae notations represent a chemical equation.

Balanced Chemical Equations

In chemical reactions, laws of conservation of mass hold. That is the total mass before and after the reaction remains constant and does not change.

When more than one reactant is involved in a chemical reaction, one reactant oxidizes while the other reduces, causing oxidation and reduction to occur simultaneously. This process is known as a redox reaction.

Types of Chemical Reactions

1. Endothermic Reaction

When the heat is soaked up by the reactants from the environment it is called an endothermic reaction.

Example :

1. Melting ice cubes
2. Evaporating liquid water

 

2. Exothermic Reaction

Chemical reactions in which the heat moves from the internal environment to the external environment, that is heat is given out, are called exothermic reactions.

Example :

1. Combustion
2. Rain

Let us consider an experiment where the teacher gives two salts.  Ammonium nitrate (NH₄ NO₃) and calcium chloride (CaCl₂). The teacher asks to put these salts in water and observe the changes. We know that water and salt are in a flask. Let us consider the flask as the outer environment.

When we added ammonium nitrate, the reaction absorbed heat from the surroundings and made the flask cold. This indicates an endothermic reaction. While adding CaCl₂ , heat is released into the environment. This represents an exothermic reaction.

One method to learn this is exo-heat given to the external environment!

Oxidation and Reduction Reactions / Redox Reactions

When a reactant combines with oxygen, it is said to be oxidized and that is called oxidation. Whereas, when a reactant gives away the oxygen, it is said to be reduced and is called reduction.

Observers noted in the above reaction that copper loses oxygen and undergoes reduction, while hydrogen gains oxygen and undergoes oxidation.

Redox Reactions

In a chemical reaction involving more than one reactant, one reactant undergoes oxidation while the other undergoes reduction. This simultaneous process of oxidation and reduction is termed a redox reaction.

Effects of Oxidation and Reduction in Everyday Life

These scientific processes also affect daily life activities, for example

1. Corrosion:

Iron reacts with moisture present in the air and the oxygen, and gets rusted. This is called corrosion.

Similarly, when elements like silver and copper come into contact with moisture and oxygen, they undergo a color change, turning black and green respectively. This color change is also a result of corrosion.

2. Rancidity:

This process oxidizes food products containing fats and oil, resulting in a change in color and smell.

FAQ

1. What is the total number of marks the chapter has?
   This chapter comprises a total of six marks. It makes 7.5 %.
2. What are the important topics in this chapter?
   Some of the most important topics include Balancing the chemical equation, types of reactions, and the effect of oxidation reactions.
3. How can ToppersSky help in scoring full marks?
   You can complement your learning by watching toppersSky videos and can make the best use of its different videos.
4. How many hours of everyday study can help?
   Studying for two hours every day can help in doing good preparations.