Chemical Changes

 CHEMICAL CHANGES

Chemical Changes refer to processes where one or more substances are transformed into new substances with different properties. These changes are usually irreversible under normal conditions.

Key Features of Chemical Changes:

1. New substances are formed (with new chemical compositions).

2. Energy is often absorbed or released (heat, light, or sound).

3. Change is usually irreversible.

4. Properties of the new substances are different from the original ones.

5. A chemical reaction takes place.

Examples of Chemical Changes:

Burning of wood or paper

Rusting of iron

Cooking food

Digestion of food

Souring of milk

Baking a cake

Vinegar reacting with baking soda

Signs of a Chemical Change:

Change in color

Formation of a gas (bubbles or fizzing)

Change in temperature

Production of light or sound

Formation of a precipitate (solid formed from two liquids)

⚠️ Reaction of Sodium with Water

When sodium (Na) reacts with water (H₂O), it is a vigorous and exothermic chemical reaction that produces sodium hydroxide (NaOH) and hydrogen gas (H₂).

🔬 Chemical Equation:

2 Na + 2 H₂O  →    2 NaOH + H₂↑ + heat

🔥 What Happens During the Reaction:

Sodium floats on water (it is less dense).

It moves rapidly on the surface due to the release of hydrogen gas.

Heat is released, which may ignite the hydrogen gas.

Sometimes, a small flame or pop sound is heard.

A basic solution of sodium hydroxide forms in water.

📌 Observations:

Fizzing or bubbling (due to hydrogen gas).

Heat and sometimes fire.

Formation of a colorless solution (NaOH).

The solution turns red litmus blue (indicating it is basic).

⚠️ Safety Note:

Sodium is a highly reactive metal.

The reaction is dangerous and should only be performed under supervision and in small quantities.

Stored under oil to prevent reaction with moisture in the air.