Lessons 3-5

Lesson 3
Lesson 3 describes the differences between physical and chemical changes. A physical change is a change in matter in which a substance changes form but not identity. A chemical change is a change in matter that results in the formation of a new substance with new properties. Dissolving is considered a physical change. However, ionic compounds do not dissolve the same way as molecular solids.

Practice Problems
6A. Chemical, the equation has changed
6B. Physical, it is the same compound

Lesson 4
Lesson 4 was about the law of conservation of mass. this law states that mass can not be created or destroyed in a physical or chemical change. The exception to this is when you have a gas product. If the gas is not trapped some mass will be lost because it is impossible to account for all gas mass if it is not contained. Individual atoms are conserved in chemical reactions and physical changes. From start to finish the number of atoms in each element stays the same.

Practice Problem
4. C

Lesson 5
Lesson 5 taught us how to balance  chemical equations. To do this always start with the element that only shows up once on each side of the equation. Also when balancing equations you can only change the coefficient.

Practice Problem
1. Chemical equations need to be balanced because mass cannot be created or deswtroyed during the change.