Chemical Equations

1
Chemical Equations
2
Chemical Equations

• Reactants written on left
• Products written on right
• Conditions are written over/under the arrow

3
Symbols used in chemical equations

• separates 2 or more reactants or products
• -gt separates reactants from the products
• (s) identifies solid state
• (l) identifies liquid state
• (g) identifies gas state
• (aq) identifies water solutions

4
Word Equations

• Chemical equations written using words instead of
  chemical formulas.
• When writing out chem equations remember the 7
  diatomic molecules.
• I2 Br2ought Cl2ark H2ome O2n F2riday N2ight

5
Conservation of Mass

• What goes in must come out

• Atoms and masses are conserved in chemical
  reactions (rxns)

• meaning you must have equal masses on each side
  of the equation
• of products must the of reactant

6
Balancing Equations

• Coefficients indicate the number of moles of
  reactants and products.

• Coefficients can only be written in the front of
  a compound

• Good Example 2H2 O2 ? 2H2O
• Bad Example 2HCl Mg ? H2 Mg2Cl

7
Balancing Equations

• You can not change the subscript only the
  coefficient
• Coefficient typically is a whole number
• Put coefficients in the front of a compound not
  in the middle

8
Balancing Equations

• 1. Convert word equation to the text format
• 2. Write the correct compounds (balanced
  charges)

• Sodium carbonate reacts with hydrogen chloride to
  produce sodium chloride and carbon dioxide

• Na2CO3 HCl ? NaCl CO2 H2O

9
Balancing Equations

• 3. Count the number of atoms on each side of the
  equation (tally)

10
Balancing Equations

• 4. Insert coefficients for one element at a time
  so it is equal on both sides
• 1st balance atoms that appear only once on each
  side
• Balance remaining
• Leave H and O to the end
• If there is a polyatomic ion and it stays the
  same on each side of the equation treat it as a
  unit.

11
Balancing Equations

• Remember when you tally the number of atoms in a
  compound that the atoms in parenthesis are
  multiplied by the number outside

12
Balancing Equations

• Examples
• ___ NaNO3 ___ PbO ? ___ Pb(NO3)2 ___ Na2O

13
Balancing Equations

• Examples
• ___ AgI ___ Fe2(CO3)3 ? ___ FeI3 ___ Ag2CO3

14
Balancing Equations

• Examples
• ___ NaNO3 ___ PbO ? ___ Pb(NO3)2 ___ Na2O

15
How much does an atom weigh?

• Look at the periodic table.
• C 12.011g
• N 14.06 g
• O 15.999 g

16
Molar Relationships

• Molecular weight
• The sum of the atomic weights of atoms in a
  molecule.
• Formula weight
• The sum of the atomic weights of atoms in a
  formula unit.