This document discusses physical and chemical changes, using the burning of magnesium ribbon as an example of a chemical change. It notes that a chemical change results in a new substance being formed, is irreversible, and can produce heat, light, gases or smells. When magnesium ribbon burns in oxygen, it forms magnesium oxide, a white ash, demonstrating that a new substance is created in a chemical reaction.

1. Grade: 7
Subject: SCIENCE
CH – 6 Physical and Chemical changes

2. PROPERTIES OF CHEMICAL CHANGES
• Heat, light or any other
radiation (ultraviolet, for
example) may be given off
or absorbed.
• Sound may be produced.
• A change in smell may take
place or a new smell may be
given off.
• A colour change may take
place .
• A gas may be formed.
• A NEW SUBSTANCE IS
FORMED

3. PHYSICAL VS CHEMICAL CHANGES
PHYSICAL CHANGES CHEMICAL CHANGES
1. These are changes in the physical
properties like shape, size, colour and
state.
1. These are changes in the chemical
nature of the substances.
2. No new substance is formed. 2. New substances are always formed.
3. Most physical changes are reversible. 3. These are irreversible changes.
4. No striking change can be observed. 4. The changes can be seen very clearly.
Heat, light, gases, smell are given off.
Colour change may occur.

5. BURNING OF MAGNESIUM RIBBON
• Magnesium is a chemical element with
the symbol Mg. It is a shiny gray solid.
• Magnesium is the ninth most abundant
element in the universe.

6. IMPORTANT REACTIONS
• Magnesium (Mg) + Oxygen (O2) →Magnesium
oxide (MgO)
MAGNESIUM RIBBON (SHINY GRAY) BURNS IN THE
PRESENCE OF OXYGEN TO FORM MAGNESIUM OXIDE
(WHITE ASH).

7. IMPORTANT REACTIONS
• On adding some water to Magnesium Oxide
• Magnesium oxide (MgO) + Water (H2O) →
Magnesium hydroxide [Mg(OH)2]
• Now a Litmus Test is done to determine the
nature of Magnesium Hydroxide.
• When the Litmus Papers are used – It shows
that the Blue Litmus remains unchanged but
the Red Litmus turns Blue – suggesting that it
is basic in nature.

8. CONCLUSIONS
• Burning of Magnesium ribbon is a chemical
change. In fact, burning of any substance is a
chemical change.
• Burning is always accompanied by production
of heat, light and a lot of gases are given off.
• Burning of Magnesium produces a White
Light.
• White Ash (Magnesium Oxide) – a new
substance is formed in this reaction.
• The Ash (Magnesium oxide) on further
reaction with water forms a basic hydroxide.