1. Unit 6:
Chemical Reactions,
Equations,
Moles & Stoichiometry

2. (coefficient x subscript = total # of atoms of element)
Chemical Reaction Equations
Remember:
Chemical change  =  chemical reaction Chemical equation → describes the change: how reactant(s) turn into product(s)
Reactant(s) → Product(s)
 2H2(g)     +   O2(g)   →    2H2O(l)
Symbols in a chemical equation
→ (to yield, produce, or form)
(s)(l)(g)(aq)  state of matter symbols (aq = Aqueous solution/dissolved in water)
H2  subscript: quantity of element or compound
2H2 coefficient: used to balance equation
(coefficient x subscript = total # of atoms of element)

3. Balancing Chemical Equations
Antoine Lavoisier wrote in 1785:
"Nothing is created, either in the operations of art or in those of nature, and it may be considered as a general principle that in every operation there exists an equal quantity of matter before and after the operation; that the quality and quantity of the constituents is the same, and that what happens is only changes, modifications.”
The Law of Conservation of Mass:
“Matter is neither created nor destroyed.”
For us this means we must have the same number of atoms of each element before and after a chemical reaction.
How to balance a chemical equation?
Count!