PHYSICAL CHANGES do not produce a new substance.

This means no new products are formed. As a result, there is no change in temperature, colour, and smell. Gases are not produced. so bubbles won't be present.

Examples are:

• Changes in state (MELTING, FREEZING, EVAPORATION, CONDENSATION, SUBLIMATION etc.)

• Bending a piece of wire

• Breaking a bottle.

Usually, physical changes are reversible.

A CHEMICAL CHANGE occurs when a new substance is formed and is not easily reversible.

Observations to show a chemical change could be a colour change, a new smell, the chemicals getting hotter or colder or a gas is produced.

For example:

• Burning wood - temperature change

• Mixing acid with universal indicator - colour change

• Seeing bubbles when vinegar and baking soda are mixed - a gas is formed

• Burning sulfur - creates a new smell.

To observe reactions means to record or make note of something we have experienced. We also think of observations as watching something, but in Science, observations may be made with any of our senses (by seeing, feeling, hearing, tasting, or smelling) or even using tools to make observations that are then changed into something our senses detect.

Observation tools include thermometers, miceoscopes telescopes, radars, computer sensors, and probes. Sometimes these tools can observe and collect data that humans cannot directly sense. By using these tools, scientists can often make many more observations and much more precisely than our senses are able to.