Unit 6: Chemical Reactions, Equations, Moles & Stoichiometry

(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)

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!