Chapter 2 – section three - Physical Changes

• Physical changes do not change a substance’s identity.
• Physical changes affect only the physical properties of a substance.
• Physical change a change of matter from one form to another without a change in chemical properties
• Dissolving is a physical change.
• When a substance dissolves, the molecules of the substance do not change.
• Dissolving a solid in a liquid, a gas in a liquid, or a liquid in a liquid are all physical changes.
• Mixtures can be physically separated.

Separating Mixtures

• Because mixtures are not chemically combined, each component of the mixture has the same chemical makeup it had before the mixture was formed.
• Mixtures can be separated based on their physical properties.

Chemical Changes

• Chemical changes happen everywhere.

• Examples of chemical changes include:
• burning
• rusting
• digesting
• decomposing

• Chemical change a change that occurs when a substance changes composition by forming one or more new substances

Chemical Changes

• Chemical changes form new substances that have different properties.

• The results of a chemical change are substances that have completely different properties from the properties of the original substances.
• Chemical changes can be detected.

• Changes in physical properties can be an indication of a chemical change.

• Examples include:
• change of color
• change of smell
• fizzing
• production of heat
• production of sound
• production of light
• Chemical changes cannot be reversed by physical changes.

Because new substances are formed in a chemical change, the change cannot be reversed by using physical changes.

• Many chemical changes are impossible to reverse, for example it is impossible to “unbake” a cake.
• Compounds can be broken down through chemical changes.

• Some compounds undergo chemical changes to form elements, others break down to form simpler substances.