Chemical Reactions
Chemical reactions result from mixing of substances or breaking down of substances to form new substances of a different property. These reactions are everywhere - such as when the food cooks, metal rusts, or our body digests the food. Knowledge of such changes provides an explanation and prediction of the behavior of matter in different circumstances.
1. Physical vs. Chemical Changes
Physical Changes: Such changes are those that alter the condition or how a substance looks but not its aspect of chemical constitution. It is the same substance in terms of molecules.
Examples:
- Melting ice
- Tearing paper
- Dissolving sugar in water
Chemical Changes: It is through such changes that new substances of the different chemical properties are formed. There is a chemical change in the original substance.
Examples:
- Burning wood
- Rusting of iron
- Baking a cake
2. Indicators of Chemical Reactions
Scientists search for some indications that will indicate if there has been a chemical reaction. These indicators include:
Change in Color: A material changes colour, thereby showing that its other substance had been formed.
Formation of Gas: The bubbles or the fizzing can be observed which indicates that there has been gas production.
Change in Temperature: Heat is added or removed when the reaction takes place, thus causing change of temperature.
Formation of Precipitate: A change to a solid from the solution in a liquid form is a chemical change.
Emission of Light or Sound: Light or sound is generated on reaction.