6th Class Science Changes Around us Changes Around Us

Changes Around Us

Synopsis

Types of changes

• Changes can also be classified based on the rate at which they take place.

• Fast change: The change that takes place within a very short time.

• Slow change: The change that occurs over a long period of time.

• Another factor for change is uniformity with respect to time.

• Periodic changes: Changes that repeatedly occur at fixed intervals of time e.g., change of seasons, formation of day and night.

•  Non-periodic changes: Changes that do not repeatedly occur at fixed intervals of time are non-periodic e.g., occurrence of storms and rain.

• Reversible change: A change in which the original substances can be retrieved. e.g., mixing of iron particles and sulphur.

• Irreversible change: A change in which a new substance is formed and the original substances cannot be retrieved, e.g., heating a mixture of iron pieces and sulphur.

• Exothermic reaction: A change in which heat is released e.g., burning of coal.

• Endothermic reaction: A change in which heat is absorbed e.g., evaporation of water.

• When substances react with each other, they require the right conditions like temperature, pressure, light, catalyst, etc. The rate and the extent of change depends on these conditions.

• Unstable substances undergo change easily.

• Differences between physical and chemical changes: