Chemical Equations

Chemical Equations Classifying, Predicting, Balancing

To Write an Equation Given: reactants  ? What to do: - Classify the reaction as one of 5 types - Based on how the reaction works, write what products will form - Balance the equation with coefficients

Classifying Equations • Synthesis A + B  AB elem + elem  compound Examples (unbalanced): Na + O2  Na2O Mg + N2  Mg3N2 K + P  K3P

Classifying Equations • Decomposition AB  A + B compound  elem + elem There are also other types of specific decomposition reactions carbonates: MCO3  MO + CO2 chlorates: MClO3  MCl + O2 Examples (unbalanced): NaCl  Na + Cl2 Na2CO3  Na2O + CO2 Fe2O3  Fe + O2 KClO3  KCl + O2 K2S  K + S

Classifying Equations • Single Replacement A + BC  AC + B A + BC  BA + C elem + cmpd  cmpd + elem Examples (unbalanced): Ca + HCl  CaCl2 + H2 NaCl + F2  NaF + Cl2 Sr(NO3)2 + Li  LiNO3 + Sr

Classifying Equations • Double Replacement AB + CD  AD + CB cmpd + cmpd  cmpd + cmpd Examples (unbalanced): HCl + NaOH  NaCl + HOH AgNO3 + CaCl2  AgCl + Ca(NO3)2 Li3PO4 + KNO3  LiNO3 + K3PO4

Classifying Equations • Combustion of a hydrocarbon C_H_ + O2 CO2 + H2O hydrocarbon + oxygen  carbon dioxide + water Examples (unbalanced) C3H8 + O2  CO2 + H2O C4H10 + O2  CO2 + H2O C6H12O6 + O2  CO2 + H2O

Classifying Practice, Part 1 Classify the following reactions: Na + RbCl  NaCl + Rb CH4 + 2O2  CO2 + H2O H2SO4 + 2NaOH  2HOH + Na2SO4 NaCl + AgNO3  AgCl + NaNO3 2NaCl  2Na + Cl2 F2 + 2LiCl  2LiF + Cl2 AlCl3 + KOH  Al(OH)3 + KCl Cl2 + 2NaI  2NaCl + I2 2Sn + O2  2SnO 2HCl  H2 + Cl2 2C3H6 + 9O2  6CO2 + 6H2O

Classifying Practice, Part 2 Classify the following reactions: Cl2 + LiBr  NaCl + Ag2SO4  C2H4 + O2  Na + RbBr  KCl  Ba + N2 C2H6 + O2  AlF3 + KOH  HCl + NaOH  Cl2 + KI  Fe + O2  HF 

Predicting Products Based heavily in being able to write formulas. • element names = symbols from periodic table • “silver” = Ag; “carbon” = C; “aluminum” = Al • 7 diatomic elements: “hydrogen” = H2; “nitrogen” = N2; “oxygen” = O2; “fluorine” = F2; “chlorine” = Cl2; “bromine” = Br2; “iodine” = I2 • ionic compounds: use charges to determine formula • “sodium oxide” = Na+1 and O-2= Na2O • “barium nitrate” = Ba+2 and NO3-1 = Ba(NO3)2

Predicting Products • Must classify FIRST to know how reaction works. • Use rules for writing compounds to figure out formulas for products Ca + O2 KClO3 MgSO4 + Li  NaOH + HCl C3H8 + O2 

Predicting Practice Classify the following reactions: Cl2 + LiBr NaCl + Ag2SO4 C2H4 + O2 Na + RbBr KCl Ba + N2 C2H6 + O2 AlF3 + KOH  HCl + NaOH  Cl2 + KI  Fe + O2 HF 

Balancing Equations • According to the LAW OF CONSERVATION OF MASS: • # of atoms on each side of a reaction must be the same (conserved) ___ Ca(NO3)2 + ___ NaCl ___ NaNO3 + ___ CaCl2

Wrap-Up To write a chemical equation: • Classify the equation according to the reactants • Predict what the products will be. Write their formulas according to rules of nomenclature (if in doubt, look for charges!) • Balance the entire equation with coefficients

Chemical Equations