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.

 

Review:

  1. Explain the difference between a physical property and a physical change.
  2. Give one example of a chemical change.
  3. What is the law of conservation of mass?

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