Topic: Stoichiometry: Balancing Chemical Equations

What is stoichiometry? The study of quantitative relationships in a balanced chemical equation Balance equations represent chemical reactions –Remember in chemical reactions 3 things are conserved Matter Energy charge

Law of Conservation of Matter Matter is neither created nor destroyed in a chemical reaction Mass reactants = Mass productsMass reactants = Mass products Chemical bonds in reactants may break New bonds may form to produce products Number of atoms of each element is “constant” # of atoms of each element is the same on both sides of the equation# of atoms of each element is the same on both sides of the equation

Writing Chemical Equations word equation  Begin with word equation  Solid Tin (IV) Oxide is heated with Hydrogen gas to form tin metal and water vapor. skeleton equation  Next go to skeleton equation: replace names of substances with chemical formulas  SnO 2(s) + H 2(g)  Sn (s) + H 2 O (g)  Balance  Balance skeleton equation: # of atoms of each element is the same on both sides of the equation (law of conversation of mass) - let’s figure out how to balance

Equation Balancing… let’s RAP R A P SnO 2(s) + H 2(g)  Sn (s) + H 2 O (g) Sn O H NOT BALANCED

SnO 2(s) + H 2(g)  Sn (s) + H 2 O (g) Sn O H Find the most complex compound and then compare the number of each element on product side and reactant side Look at H 2 O – 2 Hydrogen and 1 oxygen On reactant side, 2 Oxygen and 2 Hydrogen Use Coefficients to balance the numbers of each atom, check number of atoms as you go: NOTE: NEVER CHANGE SUBSCRIPTS BALANCED

NOTE: Coefficients must be in lowest possible ratios 2SnO 2(s) + 4H 2(g)  2Sn (s) + 4H 2 O (g)

Fe + O 2  Fe 2 O 3 HINTS:HINTS: –Most Complex = Fe 2 O 3 –ODDS ARE AKWARD, so Try to make O 3 even!!!!!!! 4Fe + 3O 2  2 Fe 2 O 3

AgNO 3 + MgCl 2  Mg(NO 3 ) 2 + AgCl HINTS:HINTS: –Keep polyatomics together NO 3NO 3 AgAg ClCl MgMg 2 AgNO 3 + MgCl 2  Mg(NO 3 ) AgCl

Na + H 2 O  NaOH + H 2 2 Na + 2 H 2 O  2 NaOH + H 2 HINTS:HINTS: –ODDS ARE AKWARD – try to make even H on product side H + H 2 = 3 hydrogensH on product side H + H 2 = 3 hydrogens