Physical and Chemical Changes, Solution

Which one of the following is a physical change?

[amp_mcq option1=”Burning of coal” option2=”Burning of wood” option3=”Heating of a platinum crucible” option4=”Heating of potassium chlorate” correct=”option3″]

The correct answer is C) Heating of a platinum crucible.

A physical change is a change in the form of a substance, but not in its chemical identity. Chemical changes involve a chemical reaction where new substances are formed.
– Burning of coal and wood are combustion reactions where the substance reacts with oxygen to form ash, carbon dioxide, etc. These are chemical changes.
– Heating of potassium chlorate (KClO₃) typically refers to its thermal decomposition, which produces potassium chloride (KCl) and oxygen (O₂). This is a chemical change.
– Heating a platinum crucible: Platinum is a very noble (unreactive) metal. Heating it, even to high temperatures in air, usually only changes its temperature or potentially causes thermal expansion or changes in its physical state (if heated to melting point). It does not readily undergo a chemical reaction or decomposition under normal heating conditions in a lab. Therefore, heating a platinum crucible is primarily a physical change.

Physical changes are often reversible (e.g., melting/freezing water). Chemical changes are usually irreversible without further chemical reactions. Recognizing chemical changes often involves looking for signs like color change, gas evolution, precipitate formation, or significant energy change (heat/light).

Which one of the following is an example of chemical change ?

[amp_mcq option1=”Burning of paper” option2=”Magnetization of soft iron” option3=”Dissolution of cane sugar in water” option4=”Preparation of ice cubes from water” correct=”option1″]

Burning of paper is an example of a chemical change.

– A chemical change involves a chemical reaction where one or more substances are transformed into different substances with different properties.
– Burning is a combustion reaction where paper reacts with oxygen, producing ash, carbon dioxide, water vapor, and other substances. This process forms new chemical compounds and is not easily reversible.
– Physical changes alter the form or appearance of a substance but not its chemical composition. Magnetization, dissolution, and phase changes (like freezing water) are physical changes, as the original substances retain their chemical identity and the process is often reversible.

Key indicators of a chemical change include changes in color, temperature, formation of gas or precipitate, and difficulty in reversing the process.