1. Balancing Equations and Types of Equations
Day 9

2. Classifying Reactions
Synthesis: reactions make larger molecules A + B  AB
2. Decomposition: Breaks compounds apart
AB A + B
3. Single-replacement: elements trade place
XA + B  BA + X
4. Double-replacement: exchange of ions between
two compounds
AX + BY AY + BX

4. Chemical Equations
To write a correct chem. equation, the law of conservation of mass must be taken into account.
This means…same numbers of each type of atom on each side of the equation

5. Balancing Chem. Equations
Balancing of chem. equations is done by adding coefficients (number in front of the element or compound)
Al S Al2S Not Balanced
2Al S Al2S Balanced

6. Never…. Never change a subscript to balance an equation.
If you change the formula you are describing a different reaction.
H2O is a different compound than H2O2
Never put a coefficient in the middle
of a formula
2 NaCl is okay, Na2Cl is not.

7. Learning Check E4 Fe3O4 + 4 H2 3 Fe + 4 H2O
A. Number of H atoms in 4 H2O
B. Number of O atoms in 4 H2O
C. Number of Fe atoms in Fe3O4

8. Steps in Balancing An Equation
Fe3O H Fe H2O
Fe: Fe3O H Fe H2O
O: Fe3O H Fe H2O
H: Fe3O H Fe H2O

9. Balance each equation. Add coefficients
A. Mg N Mg3N2
B. Al Cl AlCl3

10. Solutions
A. 3 Mg N Mg3N2
B. 2 Al Cl AlCl3