Class 9 (Science assignment)

 

Passage: Understanding Compounds and Chemical Reactions

Everything around us is made up of matter — and matter is made of elements. When two or more elements combine chemically in a fixed ratio, they form a compound. For example, water (H₂O) is a compound made of two hydrogen atoms and one oxygen atom. Similarly, carbon dioxide (CO₂) is formed when carbon and oxygen combine in a fixed proportion. Compounds have different properties from the elements they are made of. For instance, hydrogen and oxygen are gases, but when they combine, they form liquid water.

A chemical reaction occurs when one or more substances (called reactants) change to form new substances (called products). During a reaction, the atoms in the reactants rearrange themselves to create new combinations, but no atoms are lost or gained — this is known as the law of conservation of mass. For example, when hydrogen burns in oxygen, it produces water:

2H₂ + O₂ → 2H₂O

In this reaction, hydrogen and oxygen are the reactants, and water is the product. Chemical reactions can be seen everywhere — in cooking, rusting of iron, burning of fuels, and even in our bodies during digestion.

Questions:

1. What is a compound? Give two examples.
2. How is a compound different from a mixture?
3. Define a chemical reaction in your own words.
4. What are reactants and products? Give one example for each.
5. Write the chemical equation for the formation of water and name the reactants and product.