Test: Changes Around Us

Physical change: A physical change is any change in matter that involves the substance going from one physical state to another. When a substance undergoes a physical change it does not lose its original properties when changing from one phase to another.

Example: Ice melting involves a change from a solid to a liquid and the substances maintain the properties of water because the molecules never change.

Digestion of food is a chemical change as chemical action takes place to break the complex food into simpler substance by action of enzymes.

Growth is a chemical change.

Chemical change in a body is a change that cannot be reversed and observes a new component or substance.

The reason that growth is considered to be a chemical change is because when growth in a body or a living organism takes place metabolism changes occur.

These changes are permanent and cause structural changes in the body.

The change in which new substance with new properties is formed is called as chemical change.

If new substance are formed, the molecular arrangement of the compound has changed and hence the process is irreversible.

Physical changes are temporary change as no new substance is formed and changes can be reversed back by physical process.

Rotation of fan blade is a periodic change as it is repeated at fixed interval of time.

Melting of ice is a physical change in which substance changes its physical state but not properties.

Hence it is a reversible change in which melted ice can freeze again by decrease in temperature.

Hence the option C is correct.

Physical changes occur when objects or substances undergo a change that does not change their chemical composition.

This contrasts with the concept of chemical change in which the composition of a substance changes or one or more substances combine or break up to form new substances.

Correct Answer :- a

Explanation : In an exothermic reaction, heat is evolved, and system loses heat to the surroundings. Therefore, q_p will be negative and Δ_rH will also be negative.

Changes which are repeated after regular intervals are called periodic changes.

► The occurrence of day and night and even the change of periods in your school are examples of periodic changes.

Changes which do not take place periodically that is after a fixed period of time, such as earthquake, freezing of water to form ice, are non-periodic changes.