This chapter explains that changes are constantly happening around us in our daily life and in nature. Some changes affect only the shape, size, or state of a substance, while others lead to the formation of new substances. Based on this, changes are classified as physical changes and chemical changes. The chapter helps us understand how to identify different types of changes using simple examples like melting, burning, rusting, and cooking. It also explains concepts such as reversible and irreversible changes, combustion, and ignition temperature, showing how changes can be useful or harmful depending on the situation.
Key Points
Changes are classified into physical and chemical changes.
A physical change involves a change in shape, size, or state without forming a new substance.
Physical changes are usually reversible.
A chemical change results in the formation of one or more new substances.
Chemical changes are generally irreversible.
Rusting, burning, curdling of milk, and cooking food are chemical changes.
Combustion is a chemical change in which a substance reacts with oxygen to produce heat and light.
Substances that burn easily are called combustible substances.
Ignition temperature is the minimum temperature required for a substance to catch fire.
Some processes, like burning of a candle, involve both physical and chemical changes.
Changes can be desirable (useful) or undesirable (harmful).
Natural processes such as weathering and erosion bring slow changes on the Earth’s surface.
👉 👉Changes are a natural part of life. By understanding different types of changes and their effects, we can make better choices, use resources wisely, and reduce harmful impacts on the environment.