Physical vs. Chemical Changes Notes
Matter undergoes changes all of the time. There are two types of changes,
physical and chemical.
Physical Changes:
Physical changes occur when the appearance of a substance changes, but
chemically the substance is the same. The individual molecules do not change.
Examples of physical changes are melting, freezing, or changing size or shape. A
physical change also occurs when substances are mixed and something dissolves, like
when making salt water or Kool-Aid. The water, salt and sugar still keep their original
properties and the substances can be separated again.
Chemical Changes:
A chemical change occurs when the atoms making up matter rearrange to form
a new substance with new properties. This usually occurs during a chemical
reaction.
Evidence of a chemical change:
Evidence What You Might Observe
production of a gas bubbles foaming odor
fizzing smoke
color change
*not all color changes are chemical!!
a different color appears
formation of a precipitate cloudiness foggy
solid at the bottom of the container
change in heat or light energy temperature increases or decreases
sparks explosion glowing
These are only clues… a chemical change has not actually taken place unless matter has
changed into a new substance. Some common examples of chemical changes include
rusting, tarnishing, burning, cooking and digesting.
If you have the chemical equation, you can tell if a chemical change has taken place by
looking to see if the products in the equation are different from the reactants.
TEKS 6.5D identify the formation of a ne w substance by using the evidence of a possible chemical change such as produ ction of a gas, change in
temperature, production of a precipitate, or color change.
TEKS 8.5E investigate how evidence o f chemical reactions indicate that new substa nces with different properties are formed.
