1. Chapter 12 Lesson 2: Matter and Its Changes
Ms. Amanda and Ms. Diana

2. Changes of Matter Matter can change in many ways.
These changes can be either physical or chemical.
Physical change – a change in the size, shape, or state of matter that does not change the matter’s identity.
Example:
Only the shape of the clay has
changed. The mass of the clay
is the same.

3. Dissolving
Remember that solubility is the ability of a substance to dissolve, or mix evenly.
Dissolving is a physical change.
When the substances mix, their identities do not change.

4. Changing State Changes in the states of matter are physical changes.
When water moves from a liquid
to a solid, or liquid to gas, the
particles of water do not change.
**The particles that make up ice
are the same as the particles that
make up liquid and gas.
**Only the amount of energy of the
particles and the distance between the
particles changes.

5. Energy and Change in State
Changes in energy cause changes in the state of matter.
Energy must be added to a substance to change it from a solid to a liquid or from a liquid to a gas.
Adding energy to a substance can increase its temperature.
When the temperature increases to the boiling point, then the liquid changes to a gas.
When the temperature increases to the melting point, the solid changes to a liquid.

6. What are Chemical Changes?
Chemical change – a change in matter in which the substances that make up the matter change into other substances with different chemical and physical properties.

7. Signs of a Chemical Change
How can you tell that a chemical change has taken place?
Signs a chemical change have taken place:
Formation of Gas
Formation of a precipitate (a solid)
Color change

8. Energy and Chemical Change
All chemical reactions involve energy changes.
Thermal energy (heat) is needed for chemical changes to take place.
Heat to bake a cake
Light energy (sunlight) is needed for a chemical change to take place.
Example: Photosynthesis
In photosynthesis, light energy
is turned into sugar, water, and
carbon dioxide by plants. This
is a chemical reaction.

9. Can changes be reversed?
Some changes can be reversed and others cannot.
When a chemical change has taken place you cannot reverse the process because the substances have changed.
Example: Baking a cake
You cannot reverse the process and get back the ingredients of the cake.
Some physical changes can be reversed.
Example: changing the shape of clay.

10. Conservation of Mass
Physical changes do not affect the mass of a substance.
Example:
The mass of a piece of ice after it has melted into water is the same as the mass of the water.
Mass is conserved (unchanged) during a physical and chemical change.
Law of conservation of mass – states that the total mass before a chemical reaction is the same as the total mass after the chemical reaction.

11. Comparing Physical and Chemical Changes

12. Questions