Algebra: expressions and equations, substitution

I find that a lot of students stuggle with the big ideas in algebra. The Powerpoint covers the following topics:
1) What is Algebra?
2) Modeling expressions and equations (and the difference between the two)
3) Substitution
4) Modeling one step equations
5) Preservation of equality
My students know to write when they see the pencil at the top of the page.