This PSEB 7th Class Science Notes Chapter 6 Physical and Chemical Changes will help you in revision during exams.
PSEB 7th Class Science Notes Chapter 6 Physical and Chemical Changes
→ Change is the tendency of life. There are many changes in our daily life.
→ There are two types of changes:
- Physical changes
- Chemical changes
→ There is always a reason for the change.
→ Some changes can be controlled and some others cannot be controlled.
→ No new matter is formed in physical change.
→ Chemical changes usually cannot be reversed.
→ The properties of new substances produced in a chemical change are completely different (new).
→ Changes can be classified based on their similarities.
→ The properties of a substance such as size, measure, color, state are called its physical properties.
→ The change that takes place in the physical properties of a substance is called a physical change.
→ The magnesium strip (ribbon) is bums with bright white light.
→ When Carbon dioxide is passed through lime water, it becomes milky.
→ Chemical change produces sound, light, heat, smell, gas, color, and so on.
→ Burning is a chemical change in which there is always an outflow of heat.
→ There is a layer of Ozone in the atmosphere.
→ For the occurrence of rust both oxygen and water are required.
→ In the galvanization process, a layer of zinc is deposited on the iron.
→ Iron can be saved from rust by applying paint.
→ Large crystals can be obtained from a saturated solution of a substance by crystallisation method.
→ Physical changes: Changes in which only the physical properties of matter change and no new matter is created are called physical changes. Example: Salt solution in water.
→ Chemical changes: Changes that involve the formation of new substances with new properties are called chemical changes. Example: Burning of coal.
→ Rust: The process in which iron gets covered with a layer of brownish substance in the presence of moist air is called rust.
→ Galvanization: The process of depositing zinc on iron to protect it from corrosion is called Galvanization.
→ Crystallisation: The process of obtaining large size crystals of a soluble substance is called crystallisation.