CHEMICAL Equations

WORD EQUATION Symbolic Equation Potassium metal + oxygen gas  potassium oxide Reactants are on the left-hand side of the equation + sign means “reacts with” Products are on the right-hand side of the equation Arrow means produces/yields/ makes Symbolic Equation 4 K(s) + O2(g)  2 K2O(s) STATE OF MATTER Letters indicate the state of each compound. (aq) = aqueous/dissolved in water (s) = solid ( l ) = liquid (g) = gas COEFFICIENTS Indicates how many of each molecule there is. i.e.: there are 4 molecules of K

Conservation of Mass - total mass of the products is always equal to the total mass of the reactant

Balancing Equations 4 2 K + O2  K2O Law of conservation of mass says you must have equal number of atoms on the reactant side as there is on the product side. Compare reactants with products, which atoms are unbalanced???? Note: If there is no number as a coefficient than it is 1 You can only change the coefficients (in front of each substance) and not subscripts behind! 4 2

TIPS for Balancing Equations Balance chemical equations tips Count all atoms & recount each time Polyatomic ions (such as SO42–) can often be balanced as a whole group Balance the H’s 2nd last Balance O’s Last Always double-check after you think you are finished!

Balancing Equations Li + AlCl3  Al + LiCl 3 3 1 Lithium, 1 Aluminum 3 Chlorine 1 Lithium, 1 Aluminum 1 Chlorine Recount: 1 Lithium, 1 Aluminum 3 Chlorine 3 Lithium, 1 Aluminum 3 Chlorine Recount: 3 Lithium, 1 Aluminum 3 Chlorine 3 Lithium, 1 Aluminum 3 Chlorine 3 3

CH4(g) + O2 (g)  H2O(aq ) + CO2(g) Balancing Equations CH4(g) + O2 (g)  H2O(aq ) + CO2(g) 2 2 1 Carbon, 4 Hydrogen, 2 Oxygen  1 Carbon, 2 Hydrogen, 3 Oxygen – do O last and H 2nd last. Recount: 1 Carbon, 4 Hydrogen, 2 Oxygen  1 Carbon, 4 Hydrogen, 4 Oxygen Recount: 1 Carbon, 4 Hydrogen, 4 Oxygen  1 Carbon, 4 Hydrogen, 4 Oxygen

2 2 H2SO4 + NaF  Na2SO4 + HF Balancing Equations

2 3 2 3 4 12 6 2 7 4 Balance the following: Fe + Br2  FeBr3 Sn(NO2)4 + K3PO4  KNO2 + Sn3(PO4)4 C2H6 + O2  CO2 + H2O 2 3 2 3 4 12 6 2 7 4

Turn Word Equations into Balanced Equations Example #1: Word Equation: Solutions of lead (II) nitrate react with potassium iodide to produce solid lead (II) iodide and a solution of potassium nitrate. Skeleton Equation: Pb(NO3)2(aq) + KI(aq)  PbI2(s) + KNO3(aq) Balanced Equation: Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(aq) Example #2: Word Equation: Copper reacts with hydrogen nitrate to produce copper (II) nitrate plus hydrogen. Skeleton Equation: Cu + H(NO3)  Cu(NO3)2 + H2 Balanced Equation: Cu + 2H(NO3)  Cu(NO3)2 + H2