Section 3: Describing Matter
All matter has both physical and chemical properties. Physical properties are those that can be observed without changing the make-up, or identity, of the matter. For example, if you tear up a piece of paper, it does not change what it is made of. Similarly, if you crumple up a piece of paper, the make-up is still the same. However, if you were to set that piece of crumpled paper on fire, you have taken the paper and turned it into ash. Flammability is a chemical property, which means it’s a property that has the ability to change something into a new kind of matter with different properties. Physical properties include color, hardness, density, and boiling and melting points. Chemical properties include flammability, combustibility, acidity, and ability to rust.
A physical change is a change in size, shape, or state of matter. The substance does not change its identity when it undergoes a physical change. When water freezes, it becomes a solid, but it is still water. Its composition has not changed. Physical changes can be reversed. If we heat an ice cube, it melts back into water. A chemical change is a change from one substance to another substance. The beginning substances called reactants change into different substances called the products. A firework exploding is an example of a chemical change. It’s important to note that during a chemical change mass is neither gained nor lost.
The law of conservation of mass says that the mass of all substances present before a chemical change equals the mass of all substances after the change.