3.1 a/b Investigating Chemical Change

Investigating Chemical Change

By Peter Sherlock

Students will:

• Investigate various reactions to identify indicators of chemical change

• Use modelling to demonstrate:

  • Rearrangement of atoms to form new substances

  • Conservation of atoms in a chemical reaction

• Construct balanced equations

What is a Chemical Reaction?

• A chemical reaction involves the rearrangement of chemical bonds to produce new substances.

• At the microscopic level, electrons move and new bonds form.

• We observe these through macroscopic indicators.

1. Gas evolution

2. Precipitate formation

3. Colour change

4. Emission of light

5. Temperature change

🧪 Definition:

• Chemical Reaction: A process that rearranges bonds to form new substances.

• Macroscopic: Observable with the eye (e.g. bubbles, colour change)

​Macroscopic indicators include:

• Gas formation indicates that a new substance has formed.

• Common when reactions occur in a liquid (e.g., water).

​Example Reaction:
Hydrochloric acid + magnesium → magnesium chloride + hydrogen gas

Indicator 1 – Evolution of a Gas

• A precipitate forms when two soluble ionic solutions create an insoluble compound.

• Colour change occurs due to different bonding affecting light absorption.

Example:
Potassium iodide + lead(II) nitrate → lead(II) iodide (solid) + potassium nitrate (aqueous)

Indicator 2 & 3 – Precipitate & Colour Change

• Exothermic: Releases heat → surroundings get hotter.

• Endothermic: Absorbs energy → surroundings cool.

Example:
Hydrogen + oxygen → water
(Releases energy as heat and light)

Indicator 3 & 4 – Light Emission & Temp Change

Multiple Choice

A burning candle is a chemical reaction because:

• It produces a precipitate

• It doesn't release heat

• It emits heat and light

• It's only a change of state

Microscopic Rearrangement of Atoms

A new substance = different bonding

• Electrons are rearranged to form new molecules

Example:
Sulfur + oxygen → sulfur dioxide

🧬 Microscopic: Too small to see (e.g., individual molecules)

Multiple Choice

Which process is not a chemical reaction?

• Rusting of iron

• Making ammonia

• Exploding fireworks

• Water evaporation

Go to your Mod 3 Practical Manual

Open up Experiment - Modelling Chemical Reactions