Balancing Equations: Chemical and Nuclear

How molecules are symbolized Cl2 2Cl 2Cl2 Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH)2 Notice that the OH is a group The 2 refers to both H and O How many of each atom are in the following? a) NaOH b) Ca(OH)2 c) 3Ca(OH)2 O H Ca Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6

Balancing equations: MgO The law of conservation of mass states that matter can neither be created or destroyed Thus, atoms are neither created or destroyed, only rearranged in a chemical reaction Thus, the number of a particular atom is the same on both sides of a chemical equation Example: Magnesium + Oxygen (from lab) Mg + O2  MgO O Mg +  Mg O However, this is not balanced Left: Mg = 1, O = 2 Right: Mg = 1, O = 1

Balance equations by “inspection” From Mg + O2  MgO 2Mg + O2  2MgO is correct Mg + ½O2  MgO is incorrect Mg2 + O2  2MgO is incorrect 4Mg + 2 O2  4MgO is incorrect Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity. a) P4 + O2  P4O10 b) Li + H2O  H2 + LiOH c) Bi(NO3)3 + K2S  Bi2S3 + KNO3 d) C2H6 + O2  CO2 + H2O 5 1,5,1 b, 2,2,1,2 c 2,3,1,6, d 2,7,2,3 2 2 2 2 3 6 3.5 2 3 C2H6 + O2  CO2 + H2O 2 7 4 6

Balance these skeleton equations: a) Mg +__ HCl  MgCl2 + H2 b) __Ca + N2  Ca3N2 c) NH4NO3  N2O + __H2O d) __BiCl3 + __H2S  Bi2S3 + __HCl e) __C4H10 + __O2  __CO2 + __H2O f) _O2 + C6H12O6  __CO2 + __H2O g) __NO2 + H2O __HNO3 + NO h) Cr2(SO4)3+ _NaOH  _Cr(OH)3+ _Na2SO4 i) Al4C3 + __H2O  _CH4 + _Al(OH)3

Balance these skeleton equations: a) Mg + 2HCl  MgCl2 + H2 b) 3Ca + N2  Ca3N2 c) NH4NO3  N2O + 2H2O d) 2BiCl3 + 3H2S  Bi2S3 + 6HCl e) 2C4H10 + 13O2  8CO2 + 10H2O f) 6O2 + C6H12O6  6CO2 + 6H2O g) 3NO2 + H2O  2HNO3 + NO h) Cr2(SO4)3+ 6NaOH  2Cr(OH)3+ 3Na2SO4 i) Al4C3 + 12H2O  3CH4 + 4Al(OH)3

Returning to reaction types K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au We have looked at several types of reactions without worrying about balancing However, all equations should be balanced Predict the products and balance these: (recall, metals above replace metals below, reactions with water yield metal hydroxides) Cu + Fe2(SO4)3 Fe + CuSO4  2 3 3 Ni + NaCl  NR (no reaction) Al + CuCl2  2 3 3 Cu + AlCl3 2 Li + ZnCO3  2 Zn + Li2CO3 Li + H2O  2 2 2 LiOH + H2 ½ Al + O2  4 3 2 Al2O3

Returning to reaction types K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au We have looked at several types of reactions without worrying about balancing However, all equations should be balanced Predict the products and balance these: (recall, metals above replace metals below, reactions with water yield metal hydroxides) Fe + CuSO4  Ni + NaCl  Al + CuCl2  Li + ZnCO3  Li + H2O  Al + O2 