# Balancing Equations: Purpose: Students will be able to balance chemical equations. Warm-up: What’s the difference between the three formulas below? Cl2.

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Balancing Equations: Purpose: Students will be able to balance chemical equations. Warm-up: What’s the difference between the three formulas below? Cl Cl Cl2 one molecule two atoms two molecules

Counting Atoms 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 O H Ca How many of each atom are in the following? a) NaOH b) Ca(OH)2 c) 3Ca(OH)2 Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6

Balancing Equations: MgO
Law of Conservation of Mass: matter can neither be created or destroyed Since atoms cannot be created or destroyed, they are only rearranged in a chemical reaction The number of atoms must be the same on both sides!

Balancing Equations: MgO
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

Balancing Equations: MgO
+ Mg O However, this is not balanced Left: Mg = 1, O = 2 Right: Mg = 1, O = 1 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

Balance Equations P4 + O2  P4O10 Li + H2O  H2 + LiOH
Bi(NO3) K2S  Bi2S KNO3 d) C2H O2  CO H2O 5 2 2 2 2 3 6 3.5 2 3 e) C2H O2  CO 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) 2C4H O2  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

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