1. Chapter 24: Foundations of Chemistry
Lesson 24.3: Physical Changes
Pages
Lesson Objectives:
Students will be able to define what is a physical change
Students will demonstrate understanding of changes in the state of matter.
Students will be able to state that dissolving is a physical process
Students will be able to recognize that mass is conserved during a physical change

2. Scientific Vocabulary and Other Keywords
Melting
Boiling
Change of state
Thermal energy
Sublimation
Deposition
Dissolving
Conservation of Mass
Scientific words
Physical change

3. Although the sand has changed shape…. It is still sand.
An artist changed a flat area of sand into a masterpiece that looks very different. Is it still sand?
Yes!
Although the sand has changed shape…. It is still sand.

4. A physical change is a change in size, shape, form, or state of matter in which the matter’s identity stays the same.

5. Changing state of water
Matter such as water can change into three physical states:
Solid
Liquid
Gas
STEAM
ICE
WATER
In order to change the state of water, there needs to be:
Movement of particles
Thermal energy added or removed

6. THERMAL ENERGY Solid, Liquid and Gases
What causes the state of matter to change?
Regular arrangement of particles in a Solid

7. Adding Thermal Energy – Solid to a liquid
When thermal energy is added to a solid, the particles move faster.
The particles in the solid vibrate more, as they gain more energy
The forces that are holding the particles together become weaker
The particles are able to move more freely and the solid changes to a liquid.
This is known as the MELTING POINT
The melting point is the temperature at which a solid changes to a liquid

8. Adding Thermal Energy – liquid - gas
Once the solid has melted, adding more thermal energy will cause the particles move and vibrate even faster.
They move so fast that the forces holding them together, break apart.
The particles are then able to break free and spread out as they form a gas.
This is known as the BOILING POINT
The boiling point is the temperature at which a liquid changes to a gas and the particles spread out

9. When thermal energy is added to matter, there will be a change of state.

10. Sublimation
Unlike water, some substances that a solid, can change directly from a SOLID to a GAS, without changing to a liquid.
This is called SUBLIMATION
Sublimation of Iodine
Solid Iodine changes directly from a solid to a gas when heated.

11. Removing the Thermal Energy (Losing energy)
When thermal energy is removed, the temperature decreases and there is less energy available to the particles.
The particles will now move much slower.
When enough thermal energy is removed one of several processes may happen:
Freezing
Condensation
Deposition

12. Freezing happens when the thermal energy is removed and the particles are moving so slowly the forces between the particles hold them tightly together
Freezing and melting are REVERSE processes and happen at the same temperature.
When thermal energy is removed from a gas, the particles move slowly and the forces between them get stronger. Liquid is formed.
Boiling and condensation are REVERSE processes and happen at the same temperature.
Deposition is the change from a GAS directly to a SOLID. It is the opposite of sublimation

13. Summary:
Adding thermal energy
Removing thermal energy

14. Dissolving Sugar Solution
If you add sugar to water, eventually the sugar disappears.
It has DISSOLVED.
But it is still there.
Dissolving is a physical change.
Sugar
Water
Sugar Solution

15. = Conservation of Mass Sugar Solution 155.0g
The mass of what is made is identical to the mass of the substances that you started with.
Sugar
5.0g
Sugar Solution
155.0g
Water
150.g =

16. Question: If a sample of water has a mass of 200g and the final solution has a mass of 230g, how much solute dissolved in the water?
30g

17. Question: Which never changes during a physical change?
a. State of matter
b. Temperature
c. Total mass
d. Volume