1. Chemical Equations General form: Reactants Products For Example:
2Na(s) + Cl2(g) 2NaCl(s)
State Indicators
s (solid), l (liquid),
g (gas), aq (aqueous)
Coefficients
- from the balanced reaction
Subscripts
- based on the nature of the chemical

2. Some Vocabulary: System: Open System: Closed System:
The part of the universe being studied
Open System:
A system where things (mass,
energy) can enter and leave.
Think beaker on a hotplate
Closed System:
A system where NOTHING can enter or leave.
Think Thermos

3. The LAW OF CONSERVATION OF…
4 Conservation Laws: (all for closed systems)
The LAW OF CONSERVATION OF…
1) MASS
The mass at the beginning and the end of a chemical reaction is the same (conserved)
2) ATOMS
The total number and type of atoms in a closed system does not change during a chemical reaction.

4. 3) ELECTRICAL CHARGE 4) ENERGY
The total electrical charge in a closed system does not change during a chemical reaction.
4) ENERGY
The total energy in a closed system does not change during a chemical reaction. (The amounts of the various types of energy may change, but the total remains constant.)

5. Writing Chemical Equations From Words
Hydrochloric acid reacts with calcium carbonate crystals, producing aqueous calcium chloride, gaseous carbon dioxide and, liquid water.
Gaseous xenon hexafluoride reacts violently with water to form solid xenon trioxide and gaseous hydrogen fluoride
2HCl(aq) + CaCO3(s)  CaCl2(aq) + CO2(g) + H2O(l)
XeF6(g) + 3H2O(g)  XeO3(s) + 6HF(g)

6. Don’t Forget the Diatomics!
H2, N2, O2, F2, Cl2, Br2, I2
S and P can sometimes also bond with itself

7. Some tips for Balancing Reactions…
Start with any metals!
Then, balance anything besides H and O.
H and O are often found several times in a reaction and usually cannot be balanced until everything else is first.
Try to balance entire polyatomic groups (SO4, NO3, PO4, etc.), if possible.
To do this, the polyatomic ion would have to be found on both sides of the reaction
Diatomics can cause problems. If you get a fraction (eg. ½), multiply the equation by a whole number (eg. 2) which eliminates the fraction.

8. Try Some: __C19H17NO3 + __O2  __CO2 + __H2O + __N2
__(NH4)3PO4 + __NaOH  __Na3PO4 + __NH3 + __H2O

9. Try Some: 4C19H17NO3 + 87O2  76CO2 + 34H2O + 2N2
__(NH4)3PO4 + __NaOH  __Na3PO4 + __NH3 + __H2O

10. Try Some: 4C19H17NO3 + 87O2  76CO2 + 34H2O + 2N2
(NH4)3PO4 + 3NaOH  Na3PO4 + 3NH3 + 3H2O

11. Honours Class:
Sometimes you can get equations that are VERY difficult to balance
Try using the algebraic method!
see handout

12. The Six Basic Types of Reactions:
synthesis
decomposition
single replacement
double replacement
neutralization
combustion

13. 1) Synthesis/Combination:
General Equation:
A + B  C
one new substance is made (synthesized) by combining 2 or more reactants
Example: 2H2 + O H2O

14. You Try:
H2(g) + F2(g) →
2Al + 3S →
2HF(g)
Al2S3

15. 2) Decomposition: General Equation: A  B + C
a reactant breaks down to form two or more products (decomposes)
reverse of synthesis reaction
heat or light is generally added as a catalyst for this reaction
(Note: catalyst = substance that speeds up a chemical reaction)
Example: 2NH N2 + 3H2

16. You Try: 2 Ag2O(s) + heat → 2 NO(g) + heat → 4 Ag(s) + O2(g)
N2(g) + O2(g)

17. 3) Single Replacement: General Equation: A + BC  B + AC
either the cations or the anions in the reactants “switch places” to form new products
one element will be independent of other elements in the reactants and in the products
Example: CuSO4 + Fe FeSO4 + Cu

18. You Try: CuCl2(aq) + Fe(s) → 2CaO + 2Cl2 → FeCl2(aq) + Cu(s)
O2 + 2CaCl2

19. 4) Double Replacement: General Equation: AB + CD  AD + CB
both the cations and the anions in the reactants “switch places” to form new products
Example: LiBr + NaF LiF + NaBr

20. You Try: AgNO3(aq) + NaCl(aq) → 2NaCl(aq) + H2SO4(aq) →
AgCl(s) + NaNO3(aq)
2HCl(g) + Na2SO4(aq)

21. 5) Neutralization: General Equation: Acid + Base  Salt + H2O or
HX + MOH  MX + H2O
special case of a double replacement reaction
note a salt (ionic compound) and water are produced
Example: 2HCl + Ca(OH) CaCl2 + 2H2O

22. You Try: H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l)
H3PO4(aq) + 3KOH(aq) →
Na2SO4(aq) + 2H2O(l)
K3PO4(aq) + 3H2O(l)

23. 6) Combustion: General Equation: Hydrocarbon + O2  CO2 + H2O
note: oxygen is a reactant, and carbon dioxide and water are always produced
Example: 2C2H6 + 7O2 4CO2 + 6H2O

24. More Combustion:
Sometimes other elements are involved in the hydrocarbon (we will only look at when oxygen or sulphur are included)
Example:
C5H12O2(l) + 7O2(g) → 5CO2(g) + 6H2O(l)
C5H12S(l) + 9O2(g) → 5CO2(g) + 6H2O(l) + SO2(g)