Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Matter is everything that has mass and takes up space. It is composed of tiny particles called atoms and molecules, such as .
A Physical Change is a change in the form or state of matter without changing its chemical composition. No new substances are created. Examples include melting ice () or dissolving salt in water.
A Chemical Change (or chemical reaction) occurs when substances combine or break apart to form entirely new substances with different properties. Indicators include color change, temperature change, or the production of gas ().
The Law of Conservation of Mass states that matter cannot be created or destroyed. In any change, the total mass remains constant: .
Reversibility: Physical changes are often easy to reverse (e.g., freezing water back into ice), whereas chemical changes are usually difficult or impossible to reverse (e.g., burning wood to ash).
📐Formulae
💡Examples
Problem 1:
When you boil a pot of water, you see steam rising from the pot. Is this a physical or chemical change?
Solution:
Physical Change
Explanation:
Boiling is a change of state from liquid to gas. The molecules are still ; they have only gained kinetic energy and moved further apart.
Problem 2:
A rusty iron nail is found in the garden. The iron () has reacted with oxygen () from the air to form iron oxide (). What type of change is this?
Solution:
Chemical Change
Explanation:
This is a chemical change because a new substance, iron oxide (), has been formed through a chemical reaction between iron and oxygen. The process is generally irreversible.
Problem 3:
If you dissolve of sugar in of water, what is the final mass of the solution?
Solution:
Explanation:
According to the Law of Conservation of Mass, the mass of the parts must equal the mass of the whole: . Dissolving is a physical change.