Phase Changes and Energy Concepts

This lesson covers phase changes, explaining the differences between physical and chemical changes. Physical changes involve energy changes without forming new substances and are reversible, like water evaporating. Chemical changes create new substances and are often irreversible, like explosions. The lesson also discusses energy requirements for these changes and how they are represented on temperature vs. time graphs. Pure substances show distinct phase change plateaus, while mixtures do not.

What is a key characteristic of a physical change?

• Change in energy

• Color change

• Irreversibility

• Formation of a new substance

Which of the following is an example of a physical change?

• Melting ice

• Rusting iron

• Burning wood

• Baking a cake

What typically indicates a chemical change?

• Formation of bubbles not from boiling

• Reversibility

• Change in state

• No energy change

Which of the following is NOT a clue of a chemical change?

• Color change

• Melting

• Formation of a precipitate

• Heat production

What happens to energy during the plateau regions of a temperature vs. time graph?

• Energy is lost

• Energy is used to increase temperature

• Energy is used to change phase

• Energy remains constant

What is the process called when a solid turns directly into a gas?

• Evaporation

• Sublimation

• Deposition

• Condensation

What is the term for the energy required to change a substance from solid to liquid?

• Heat of condensation

• Heat of fusion

• Heat of sublimation

• Heat of vaporization

Which phase change involves turning a gas into a solid?

• Sublimation

• Condensation

• Deposition

• Melting

How does a mixture affect the temperature vs. time graph during phase changes?

• It creates straight lines

• It results in curvy lines

• It creates more plateaus

• It has no effect

Why do mixtures not have straight lines in a temperature vs. time graph?

• They are pure substances

• They have different substances melting at different times

• They do not undergo phase changes

• They have uniform composition