A physical change involves a change in the physical properties of a substance. Physical properties are things that can be observed without changing the type of matter. Examples of physical properties include: texture, shape, size, colour, odour, volume, mass, weight, and density. Ripping paper is an example of a physical change, since nothing new is created; we only made smaller pieces of the original paper.
An example of a compound which undergoes physical change that you have seen in your life is water (H2O, Dihydrogen monoxide). The water that comes from the kitchen tap to drink, cook, and clean is in its liquid state.
During the winter in Canada, many small lakes and rivers freeze. When this happens, the liquid water loses energy and becomes solid and some people skate on it for recreation, especially ice hockey. Ice is the solid state of water.
The last state of water is water vapour or steam. We can see this almost any day of the year when we look up to the sky on a cloudy day. Steam is used in our society to heat material for industry or it is created during the boiling of water when making dinner.
Scientists must describe different physical properties, and there are two ways to accomplish this:
Qualitative physical properties refer to observations that are made without measurement. They report on characteristics or traits. For example saying, “Metals are shiny.” is making a qualitative statement.
Quantitative physical properties refer to observations or data that includes numbers, units of measurement, and mathematical observations. For example saying, “The temperature is 20 degrees Celsius.” is making a quantitative statement.
A chemical reaction is the process by which the reactants change into new products. Essentially, the material has changed and become something new. The following are five clues that a chemical change or a chemical reaction has occurred. When making observations during an experiment, if you don't see any of the clues below, then the change is probably a physical change. Chemical properties are the potential for matter to react. This will be explained in a future activity.
Heat or light is given off. A campfire burning is an example of this chemical change.
Bubbles of gas are given off. If you see a reaction that produces a gas or bubbles through a liquid, it is a chemical change.
A precipitate forms when two liquids combine to make a solid.
A colour change is observed in the reaction. Green leaves on trees in the summer turn to reddish-orange in the fall, indicating that a chemical change has occurred in the leaves.
The change is not easily reversed as the object reacting has become something new. This fried egg cannot be uncooked. Therefore a permanent change has occurred.