Science 9: Unit B – Matter and Change Topic 2: Changes in matter

Physical Changes Any change in matter is classified into one of two groups: Physical Change – The matter changes its form, shape, and volume, but not its chemical make-up. When water freezes into ice, the chemical composition of the ice is still H2O. Other examples include mixing substances together to form a mixture: No new chemical is created in this case, just mixed together.

Chemical Changes Chemical Change – The chemical make-up of a substance is changed so that a new substance is created. These kinds of changes are pretty much irreversible. A common example of a chemical change is burning wood or paper. - Signs that a chemical change has occurred include: heat is produced or is absorbed (takes in heat from surroundings), color change, a salt/precipitate forms in a liquid, a material with different properties is produced. For the full list of signs of a chemical change see: p. 102.

Chemical and Physical Properties Any material can be described by various properties. Again, these properties are broken up into the two same properties:

Physical Properties These are properties of a substance that you can describe without having to chemically react it with another substance. Examples of physical properties include the following:

Physical Properties Cont’d Phase at Room Temperature: Is the substance a solid, liquid or gas at 25C? Melting Point: At what temperature does the substance turn from a solid to a liquid? Boiling Point: At what temperature does the substance turn from a liquid to a gas? Solubility: How well does the substance dissolve in water? Conductivity: How well does the substance conduct electricity? Density: How much does the 1 ml of the substance weigh?

Chemical Properties These properties involve how a substance reacts with another substance in a chemical reaction. For example: Wood turning black and brittle as it is being burned; hydrogen exploding when it’s ignited.

Qualitative and Quantitative Observations Qualitative Observations – observations that have nothing to do with numbers, but more to do with describing words. Describing color, texture, smell of a substance. Basically any observation made with any of your five senses (except taste of course). Quantitative Observations – Any observation where you have to write down a number or make a measurement. Usually has to do with the weight or volume of a substance.