Chemical Reactions and Equations

What happens when you leave milk at room temperature in summers? Or if you leave a nail exposed to humid air for a long time? Yes, you are right! Milk gets spoiled and the nail becomes rusty. Why does this happen? This is because a chemical reaction takes place causing a change in the milk and the nail. In fact, regular body processes such as respiration and digestion are also chemical reactions. A chemical reaction is expressed using a chemical equation. Let’s dive in and learn about chemical reactions and equations.

Suggested Videos

 

Chemical Reactions

When an initial substance goes through a chemical change, we can say that a chemical reaction has taken place. Moreover, we can say that a chemical reaction has taken place if any of the following observations occur –

• Change in state
• Change in color
• Evolution of a gas
• Change in temperature

The simplest form of representing a chemical reaction is a chemical equation. Let’s find out how to write a chemical equation.

Browse more Topics under Chemical Reactions And Equations

• Balanced Chemical Equations
• Corrosion and Rancidity
• Types of Reactions

Check out our detailed article on Chemical Reactions here.

Chemical Equations

If you were to describe a chemical reaction in a sentence, it would be quite long. To express it in a shorter form, we can write it as a word-equation. For example, the reaction between magnesium and oxygen to give magnesium oxide can be represented as follows –

Magnesium + Oxygen → Magnesium oxide

(Reactants)    →    (Product)

Substances that undergo a chemical change in a reaction are ‘Reactants’, i.e. magnesium and oxygen in the above example. The new substance formed as a result of the chemical change is the ‘Product’ i.e. magnesium oxide. In a word equation –

• The reactants and products are separated by an arrow between them.
• Reactants are written on the left-hand side of the arrow (LHS) with a (+) sign between them.
• Products are written on the right-hand side of the arrow (RHS) with a (+) sign between them.
• The arrowhead points towards the products and indicates the direction of the reaction.

Writing a Chemical Equation

Chemical equations can be further shortened if we use the chemical formulae of the reactants and products. So, if we were to write the above chemical reaction using the formulae of magnesium, oxygen and magnesium oxide, it would be written as follows –

Mg + O₂ → MgO

Now, if you count the number of atoms of each element on the LHS and RHS of the arrow, you will notice that it is not equal. Such an equation is ‘unbalanced’ because the mass is not the same on both sides. Therefore, the above equation is a skeletal chemical equation for the reaction between magnesium and oxygen.

Solved Examples for You

Question: Why are iron articles painted?

Solution: When iron comes in contact with air and moisture, a chemical reaction occurs causing the iron to rust. Painting of iron articles cuts off the contact between the iron surface and air/moisture, thus preventing it from rusting.

Question: Write the word equation and the chemical equation of the reaction between sodium and chlorine to give sodium chloride.

Solution:

Sodium + Chlorine → Sodium chloride

Na + Cl₂ → NaCl