1. Chemical Reactions

2. Goal of the class To be able to identify and balance reactions
Question of the day: Why do reactions have to be balanced?
Previous Answer: Polar molecules attract each other with their electromagnetic charge.
Previous question: How do polar molecules interact with each other?

3. → Reactions Reactions occur when bonds are broken or formed.
Every kind of bond will have some chemical energy.
Reactions are observable with large enough quantities of compounds
Always result in a chemical change →

4. Reactions Signs Many reactions can seen without any equipment
Signs of reactions
Change in colour
Production of gas
Change in temperature
Change in odour
Giving off heat, light, or energy
Formation of a precipitate

5. Chemical Equations
Chemical equations are used to show the results of a reaction
The parts that go into the reaction are the reactants
The end results are the products
The state is shown in brackets after each chemical
(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous
dissolved in water -- aq
Photosynthesis:
CO2 (g)+ H2O (l) + sunlight → C6H12O6 (s) + O2 (g)

6. Reactions and Matter
All reactions must follow the law of conservation of mass
The number of atoms must be the same on both sides
Amounts of atoms are written with coefficients.
Photosynthesis:
6 CO2 (g) H2O (l) + sunlight → C6H12O6 (s) O2 (g)
Carbon + Water → Glucose + Oxygen
dioxide

7. Balancing Reactions
Balanced equations must contain all reactants and products
Example: If you have react 1 mole of O2 with 3 moles of H2, you will have 2 mole of H2O and 1 mole of H2
3H2 + O2 → 2H2O + H2

8. Practice Balanced the following reactions: Fe + Cl2 → FeCl3
Fe + O2    →    Fe2O3
Na + H2O →    NaOH + H2.
2Na + 2H2O    →    2NaOH + H2.

9. Reaction Energies All reactions require energy in order to occur
During a reaction, energy may be released or absorbed by the reaction
Energy can be released in different ways
Typically released or absorbed as heat
Exothermic – Heat is given off
Endothermic – Heat is absorbed.
Give example of flame needed to light gas on stove.

10. Reaction Rates
Not all chemical reactions are observable by inspection.
Some require tests
Some reactions occur very quickly (explosions, biochemical changes)
Some chemical changes occur very slowly (rust, corrosion)
Talk about water’s shape and how they will learn why it’s that way

11. Vocabulary
Precipitate – to come out of a solution in solid form; a solid that exists outside of a solution
Reactants – any of the atoms or molecules that take place in a chemical reaction
Products – the remaining molecules after a chemical reaction
impossible to solve.

12. Homework
Pleases complete Chemical Interactions workbook pages up to Q20.
impossible to solve.