Balancing Equations: Chemical and Nuclear

Why do we need to Balance Chemical Equations? The Law of Conservation of Mass The # of atoms must stay the same on both sides of the equation The amount of mass is always the same.

How do we Balance Chemical Equations? We use coefficients to balance equations. Example- 2H2 +O2---> 2H2O total atoms= 4-H 2-O ---> 4-H 2-O

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 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 2 2 2 2 3 6 3.5 2 3 C2H6 + O2  CO2 + H2O 2 7 4 6

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

Here are some more to balance: a) 2KNO3  2KNO2 + O2 b) 2Pb(NO3)2  2PbO + 4NO2 + O2 c) P4 + 6I2  4PI3 d) 3MgO + 2H3PO4  Mg3(PO4)2 + 3H2O e) Br2 + 2KI  I2 + 2KBr f) Ca(OH)2 + 2HNO3  Ca(NO3)2 + 2H2O g) Bi2O3 + 3H2  2Bi + 3H2O h) 3Fe + 2O2  Fe3O4 i) 2CaO + 5C  2CaC2 + CO2

For more lessons, visit www.chalkbored.com Question 3 pg. 252 a) 2Li + 2H2O ® H2 + 2LiOH b) P4 + 5O2 ® P4O10 c) 2C2H6 + 7O2 ® 4CO2 + 6H2O d) CS2 + 3O2 ® CO2 + 2SO2 e) 2AsCl3 + 3H2S ® As2S3 + 6HCl f) 3AgNO3 + FeCl3 ® 3AgCl + Fe(NO3)3 g) 2KClO3 ® 2KCl + 3O2 h) 2SO2 + O2 ® 2SO3 For more lessons, visit www.chalkbored.com