Complex Changes & Classification

In the nineteenth century, scientist Michael Faraday delivered a famous series of lectures called the Chemical History of a Candle.

He believed that a simple burning candle was the perfect object to introduce scientific study. But why was he so fascinated by something so common?

The Physical Changes

When you light a candle, the heat of the flame melts the solid wax, turning it into a liquid. This liquid wax is then drawn up the wick and evaporates into a vapor due to the heat.

The melting, flowing, and evaporation of the wax are all physical changes. The state of the wax changes (solid to liquid to gas), but no new substance is formed.

Beyond classifying changes as physical or chemical, we also evaluate them based on how they affect us. Are they helpful, or do they cause problems?

Changes that are useful in our daily lives are called desirable changes. Examples include milk turning into curd, fruits ripening, or cooking food.