This document discusses the differences between physical and chemical changes and provides examples of evidence of irreversible chemical changes. Specifically, it notes that physical changes are reversible while chemical changes are irreversible. It then lists four main types of evidence that can indicate an irreversible chemical change has occurred: 1) a change in color, 2) a change in scent, 3) the presence of bubbles or fizzing, and 4) heat being released or absorbed during the change. Examples like iron rusting and silver tarnishing are given as illustrations of changes in color, while toasting marshmallows represents a change in scent.

1. ( Physical change )
Reversible change

2. ( chemical change )
Irreversible change

3. Evidence of irreversible change
1) Changein colour
Iron rusting Silver tarnish

4. Evidence of irreversible change
2) Changein scent ( smell )
Toasting
marshmallow

5. Evidence of irreversible change
3) Presenceof bubblesor fizzing
Antacid tablets

6. Evidence of irreversible change
3) Presenceof bubblesor fizzing
vinegar
+
Carbon dioxideBaking soda

7. Evidence of irreversible change
4) Heat isreleased or absorbed
Fire gives off heat and light

8. Evidence of irreversible change
1) Changein colour
2) Changein scent
3) Presenceof bubbles
4) Heat isreleased or absorbed