C.1 Notes: Atom Inventory & Balancing Equations

C.1 Notes: Atom Inventory& Balancing Equations Reactants --> Products Rev 6/3/04

#'s & types of atoms in Reactants #'s & types of atoms in Products = Conservation Atoms are FOREVER!! • Law of Conservation of Matter—in a chemical reaction, matter can neither be created nor destroyed – just rearranged. • The numbers & kinds of atoms present in the products are the same as those in the reactants. • Balanced equations illustrate this law.

O O O H H H H H H Atom Inventory • List atoms in reactants and products under the arrow • Determine the number of each atom. • Subscripts—show a ratio of atoms to each other in a particular compound. H2O =‘s 2 hydrogens bonded to 1 oxygen • Subscripts are NEVER changed when balancing! • Coefficients—(#’s in front of compound) show how many of each compound is present. 2H2O =‘s 2 waters

Example of Atom Inventory: CH4 + 2 O2 CO2 + 2 H2O ReactantsProducts ____ C ____ ____ H ____ ____ O ____ 1 1 4 4 4 4 What does it mean if there is no coefficient in front of the compound? Is this equation balanced? Yes!!! It is an implied “1”!

Steps to Balance • Do an atom inventory. • Balance by using coefficients to show multiple number of elements or compounds. (NEVER change subscripts to balance…is H2Othe same as H2O2?If so, would you like a big cold glass of hydrogen peroxide?!) (Coefficients only inserted in front of compound, never split compound or the ratio would D) • Recount both sides.

Example:H2 (g) + O2 (g)  H2O (l) 2 2 • Atom Inventory: Reactants Products 2 H 2 2 O 1 • Insert coefficients to balance 3. Double check to make sure it is all BALANCED! 4 4 2

Balance Al + O2 Al2O3 4 3 2 ReactantsProducts ____ Al ____ ____ O ____ 1 -- 4 -- 4 2 2 -- 6 -- 6 3 Do an atom inventory No Is this equation balanced? Use coefficient to multiplyCOMPOUND with element in it by # that balances it.

Additional Rules • Polyatomic ions, (like NO3- and CO32-) that appear on both sides of equation should be balanced as units rather than balancing their atoms individually • AgNO3+ Cu ---> Cu(NO3)2 + Ag • Balance atoms in pure elements w/ no subscripts last • Recount all atoms one last time to be sure you are correct! 2 2

Balancing Equations • For labs, demos, and whenever possible, indicate the states of each element or compound. • (s) solid (g) gas • (l) liquid (aq) aqueous • Diatomic Elements? • H O F Br I N Cl • Remember these elements need a subscript of 2 if in elemental state. If in compound then criss- cross charges to get subscripts

Practice 2 NaCl + H2SO4  Na2SO4 + 2 HCl • NaCl + H2SO4  Na2SO4 + HCl • BaF2 + Al(OH)3  Ba(OH)2 + AlF3 • 3 BaF2 + 2 Al(OH)3  3 Ba(OH)2 + 2 AlF3 • C2H6 + O2  CO2 + H2O • 2C2H6 + 7O2  4CO2 + 6H2O (had to double everything to balance oxygen)

Balanced Equations show Proportions • Coefficients show how many of each compound reacts with, or creates another substance. • Does that mean ONLY 2 hydrogen molecules will react with only 1 oxygen molecule? • NO!! Could be 250 H2 react with 125 O2

Example:2 H2 (g) + O2 (g)  2 H2O (l) • 2 H2 molecules produce 2 H2O molecules • 1 O2 molecule produces 2 H2O molecules • 2 H2 molecules react with 1 O2 molecules

Example:2 H2 (g) + O2 (g)  2 H2O (l) • Does that mean ONLY 2 hydrogen molecules will react with only 1 oxygen molecule? • NO!! Could be 250 H2 react with 125 O2

Types of Chemical Reactions Examples A + B  AB N2 + 3H2 2NH3 • Synthesis • Decomposition • Single replacement (displacement) • Double replacement (displacement) • Combustion H2O2  H2 + O2 AB  A + B A + BC  AC + B Zn + 2HCl  ZnCl2 + H2 A + BD BA + D AB + CD  AD + CB NaCl + AgNO3 NaNO3 + AgCl CxHy + O2 CO2 + H2O CH4 + 2O2 CO2 + 2H2O

C.1 Notes: Atom Inventory & Balancing Equations