Chemical and Physical Changes

8.1 - Simple Chemical Reaction

8.4 - Detecting Chemical Reactions

Physical and Chemical Changes

Physical Changes

• Physical changes keep the same chemical formula but often result in a different state.

• They do not chemically change the substance.

Chemical Changes

• Chemical changes alter the arrangement of atoms in a substance.

• Examples:

  • Iron Rusting

  • Burning

  • Cooking an Egg

  • Baking a Cake

  • Electroplating

  • Banana Rotting

  • Vinegar + Baking Soda

  • Fireworks

Physical Change

• A physical change is a change in a substance that does not alter the substance's identity.

• Examples:

  • Change in shape

  • Change in size

  • Change in phase

    • Melting (solid to liquid)

    • Boiling (liquid to gas)

    • Evaporation (liquid to gas)

    • Condensation (gas to liquid)

    • Freezing (liquid to solid)

    • Sublimation (solid to gas)

    • Deposition (gas to solid)

• Physical changes are usually reversible.

Chemical Change

• A chemical change is a change in which a substance is transformed into a different substance, altering its identity.

• Examples:

  • Burning

  • Rusting

  • Tarnishing (less bright & less shiny)

  • Decomposing

Physical vs. Chemical Change

• Examples to classify:

  • Melting cheese (Physical)

  • Burning wood (Chemical)

  • Milk souring (Chemical)

  • Wadding up paper (Physical)

  • Bicycle rusting (Chemical)

Physical Changes - Water Example

• Water (H2O) can exist in different states: solid, liquid, and gas.

• No new substance is formed; chemical composition remains the same.

Chemical Changes - Iron & Sulphur

$\text{Iron} + \text{Sulphur} \rightarrow \text{Iron Sulphide}$

• Iron and Sulphur are reactants and Iron Sulphide is the product.

Burning

• A new substance is formed which is ash.

• The chemical composition of ash differs from the original paper.

Burning Magnesium

$\text{Magnesium} + \text{Oxygen} \rightarrow \text{Magnesium Oxide}$

Difference Between Physical and Chemical Changes

• Physical Change:

  1. Only physical properties (color, physical state, density, volume, etc.) change; chemical properties remain unchanged.

  2. No new substance is formed.

  3. Very little or no energy is absorbed or given out.

  4. Temporary change.

  5. The original form can be regained by simple physical methods.

  6. Reversible.

• Chemical Change:

  1. Chemical composition and chemical properties undergo a change.

  2. A new substance is formed.

  3. Always accompanied by absorption or evolution of energy.

  4. Permanent change.

  5. Original substance cannot be obtained by simple physical methods.

  6. Irreversible.

Chemical Reactions

• There are 5 types of chemical reactions that cause chemical changes to occur.

Evidence of Chemical Change

• Evidence may include:

  • A color change

  • An odor change

  • Formation of a precipitate (mixing two liquids to form a solid)

  • Gas is formed (bubbles)

  • Changes in physical properties

  • Change in pH

Clues of Chemical Change

1. Color change:
   $\text{Copper Oxide (black)} + \text{Sulfuric acid} \rightarrow \text{Copper sulfate (blue)} + \text{Water}$

2. Heat is produced & Bubbles of Gas are formed.
   $\text{Zinc} + \text{Sulfuric acid} \rightarrow \text{Zinc sulfate} + \text{Hydrogen}$
   $\text{Potassium} + \text{Water} \rightarrow \text{Potassium hydroxide} + \text{Hydrogen}$

3. Change in pH

   • Neutralisation reaction:
     $\text{Sodium hydroxide} + \text{Hydrochloric acid} \rightarrow \text{Sodium hydroxide} + \text{Water}$

4. A precipitate is formed:

   • When two solutions (liquids) are mixed, a solid (precipitate) is formed.
     $\text{Silver nitrate} + \text{Calcium chloride} \rightarrow \text{Silver chloride (white precipitate)} + \text{Calcium nitrate}$
     $\text{Lead nitrate} + \text{Potassium iodide} \rightarrow \text{Lead iodide (yellow precipitate)} + \text{Potassium nitrate}$

5. A new odor is made.

Quiz Time! - Mimicking the Structure & Style in the last couple of pages

In the later part of the transcripts, references are made to some life science experiments.

• Which life cycle is most similar to a chemical change?

  • Why?

    • Grasshopper = Egg -> nymph -> adult

    • Butterfly = egg -> larva -> pupa -> adult

Quiz Time!

• What type of reaction is most likely occurring here?

  • How do you know?

Quiz Time!

• What type of reaction is most likely occurring here?

  • How do you know?