Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Matter is anything that has mass and takes up space. It exists in three main states: solids, liquids, and gases.
A reversible change is a physical change that can be undone. Examples include melting, freezing, and evaporating. For instance, ice () melting into water () can be reversed by cooling.
An irreversible change is a chemical change where new substances are formed and cannot be turned back into the original materials. Examples include burning, cooking, or rusting ().
Dissolving is often a reversible change. When salt () is dissolved in water, the water can be evaporated to leave the salt crystals behind.
The temperature at which water changes state is specific: it freezes/melts at and boils/condenses at .
📐Formulae
💡Examples
Problem 1:
You have a mixture of sand and salt. How can you separate them using a reversible change?
Solution:
Add water to dissolve the salt, filter the sand out, and then evaporate the .
Explanation:
Dissolving salt is a reversible change. By heating the solution to , the water turns to steam, leaving the solid behind.
Problem 2:
Is burning a piece of wood a reversible or irreversible change? Explain using scientific terms.
Solution:
Irreversible change.
Explanation:
When wood burns, it reacts with oxygen () to create new substances like ash and carbon dioxide (). These new substances cannot be converted back into wood.
Problem 3:
What happens to the particles of a solid when it reaches its melting point of ?
Solution:
The particles gain energy and begin to move past one another.
Explanation:
At , the thermal energy overcomes the fixed bonds in the solid lattice, causing a phase change from to .