TEAS® Science Study Guide
Chemical Reactions
In a reaction, reactants (left side) become products (right side), shown with an arrow: reactants → products.
The law of conservation of mass
Matter is never created or destroyed. Every atom on the left must appear on the right — which is why equations must be balanced. You balance by adjusting coefficients (the big numbers in front of compounds), never by changing the subscripts within a formula.
Common reaction types
- Synthesis — Two or more substances combine into one (A + B → AB).
- Decomposition — One substance breaks into two or more (AB → A + B).
- Single replacement — One element swaps in for another.
- Double replacement — Two compounds exchange partners.
- Combustion — A fuel reacts with oxygen, releasing energy.
Terms to know
- Reactant — A starting substance. Product — A substance formed.
- Coefficient — The number placed in front of a compound to balance an equation.
- Conservation of mass — Atoms are neither created nor destroyed in a reaction.
What the TEAS asks most
- What does a balanced equation demonstrate? Conservation of mass.
- What do you change to balance an equation? Coefficients, not subscripts.
- Reactants are on which side? The left, before the arrow.
- What type of reaction breaks one compound into several? Decomposition.