Ch 04.6: Chemical Changes

Ch 04.6:
Chemical Change

By the end of this lesson, you will be able to:
1. Define chemical change.
2. Give examples of chemical changes.

3. List signs that a chemical change has occurred.

4. Explain how some chemical changes can be reversed.
5. Describe the Law of Conservation of Mass.

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

- the new substance produced has different chemical and physical properties than the original substance

- also called a chemical reaction

Multiple Choice

In any chemical change, matter changes into an entirely different substance with different chemical properties

• true

• false

Multiple Choice

All of the following are chemical changes except ___.

• iron rusting

• ice cubes melting

• pennies tarnishing

• food spoiling

Multiple Choice

Which of the following is a chemical change?

• using soap to clean grease out of clothing

• painting a fence

• an apple rotting

• making an ice cream sundae

Multiple Choice

Which of these is a chemical change?

• water evaporating

• dissolving salt in water

• ice cubes melting

• baking a cake

Many times, changes in physical properties are the only signs that a chemical change has occurred.

- the only sure sign of a chemical change is the formation of a new substance

Evidence of a chemical change include:

formation of a gas

- bubbles, fizzing, or odor

Evidence of a chemical change include:

formation of a precipitate

- a solid (new substance) that sometimes forms when two liquids combine

Evidence of a chemical change include:

unexpected color change or rusting

Multiple Choice

Iron rusting is a physical change.

• true

• false

Evidence of a chemical change include:

the release of thermal energy (unexpected temperature change)

Evidence of a chemical change include:

the release of light, loud sound, smoke, or fire

Evidence of a chemical change include:

tarnishing

Evidence of a chemical change include:

food spoiling

Multiple Choice

A physical change occurs when food spoils.

• true

• false

Multiple Select

Signs that a chemical change has occurred include ___.

• a change in color

• the release of bubbles

• the production of an odor

Multiple Choice

An example of a property that could change only if a chemical change occurs is ___.

• size

• shape

• volume

• flammability

Chemical changes often cannot be undone. Some can be reversed, but only by other chemical changes.

Multiple Choice

Chemical changes often cannot be reversed because they produce new chemical substances.

• true

• false

The total mass of a substance does not change during a physical or chemical change.

Law of Conservation of Mass - the total mass before a chemical reaction is the same as the total mass after the chemical reaction

Multiple Choice

Ice melting is an example of a chemical change in matter.

• true

• false