Properties and Changes of Materials - Reversible changes (dissolving, melting, evaporating)
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Reversible changes are physical changes that can be undone to get back the original materials. These include changes of state and dissolving.
Melting is the process where a solid turns into a liquid when heat energy is added, such as .
Evaporating is the process where a liquid turns into a gas, usually by heating, such as .
Dissolving happens when a solid (the solute) incorporates into a liquid (the solvent) to form a . This is reversible because the solvent can be evaporated to leave the solute behind.
Conservation of Mass: In any reversible change, the total mass of the materials remains the same. For example, the mass of .
Freezing and Condensing are the reverse processes of melting and evaporating, involving the removal of heat energy.
📐Formulae
💡Examples
Problem 1:
A student dissolves of salt () into of water (). What is the final mass of the solution, and how can the salt be recovered?
Solution:
The final mass is . The salt can be recovered through evaporation.
Explanation:
According to the law of conservation of mass, . Since dissolving is a reversible change, heating the solution will cause the to evaporate, leaving the crystals behind in the container.
Problem 2:
Explain the state change that occurs when an ice cube at is left on a warm counter.
Solution:
Explanation:
The ice cube absorbs thermal energy from the environment, causing a physical change from a solid state to a liquid state (melting). This is reversible by placing the liquid back into a freezer to remove heat.