1. Chemical Reactions

2. What are chemical reactions?
There are 6 major chemical reactions we need to study in this course
A chemical reaction has occurred when the starting chemical species (reactants) is different from the final chemical species (product)
Reactants → Products
The arrow shows the direction in which the reaction takes place, but the arrow does not explain time. The reaction can take a long time or short time.

3. Closed Systems
We want this system as it is our ideal system and we can do calculations
But very rare in nature
Must be done in very specific ideal conditions
Very expensive and hard to maintain
But open systems do not conserve anything, so we must always assume.

4. Synthesis
A synthesis reaction is when two or more reactants combine to form one single product
A synthesis reaction releases a lot of energy in the form of heat or light
A + B → AB
2H2(g) + O2(g) → 2H2O(l)
2Al(s) + 3Cl2(g) → 2AlCl3(s)

5. Synthesis What to look for? How to predict the products?
We look for two elements reacting
How to predict the products?
We assume that the product is made up of the two elements reacting and joining together
So we write their product as if we are writing the formula for the chemical
Al + Cl2 will be Al3+ and Cl- so it will form AlCl3 and then we balance.

6. Decomposition It is the opposite of a synthesis reaction
A single compound breaks apart into two or more elements
Energy is absorbed as it takes energy to break the bonds inside a compound to break it into individual elements
Need light, heat, or electricity
AB → A + B
2H2O(l) → O2(g) + 2H2(g)
2KClO3(s) → 2KCl(s) + 3O2(g)

7. Decomposition What to look for? How to predict the products?
A single molecule on the reactant side
How to predict the products?
The single molecule will break into elements
So the product will be made up of the elements that the single molecule is made of
H2O is made up of H2 and O2, remember they are diatomics.
FeCl3 is made up of Fe and Cl2

8. Single Replacement
A single replacement is when one element that is alone trades place with another element in a compound
A + BC → AC + B
CuCl2(s) + Fe(s) → FeCl2(s) + Cu(s)
Zn(s) + 2HCl(aq) → ZnCl2(g) + H2(g)
This usually happens when a more reactive element kicks off the less reactive element that is in the compound
We will go more into this in the periodic trends

9. Single Replacement What to look for? How to predict the products?
An element will be reacting with a compound
How to predict the products?
The compound which contains a metal and non-metal
If the element is a metal, it will switch out with the metal in the compound
If the element is a non-metal, it will switch out with the non-metal in the compound

10. Double Replacement This happens between two ionic compounds
It is when the metal (cation) and the non-metal (anion) switch partners
AB + CD → AD + CB
2NaCl(s) + H2SO4(aq) → 2HCl(aq) + Na2SO4(s)

11. Double Replacement What to look for? How to predict the products?
Two ionic compound
How to predict the products?
The products will be the swapping of partners of the metal and non-metal
Usually, this reaction takes place to form water or to form an insoluble compound (solid precipitate).
You will learn more in Chemistry 12.

12. Acid/Base Neutralization
A form of double replacement
Where an acid reacts with a base and neutralizes
Acids are compounds that start with an H
HCl, H2SO4, HNO3 etc etc (not always the case)
Bases are compounds that contains OH at the end of their name
KOH, NaOH, Ca(OH)2 etc etc (not always the case)
The product always produces water (H2O) and a salt (ionic compound)

13. Acid/Base Neutralization
HA + BOH → HOH + BA
HCl(aq) + NaOH(aq) → HOH(l) + NaCl(s/aq)
2KOH(aq) + H2SO4(aq) → 2H2O(l) + K2SO4(aq)
HOH = H2O
A salt is any ionic compound that is neutral and doesn’t contain H at the start of their name or OH at the end of their name

14. Acid/Base Neutralization
What to look for?
An acid and base reacting
How to predict the products?
The products will always form water (H2O) and the salt will be the metal and non-metal left over.

15. Combustion
A combustion reaction is a reaction that is between a hydrocarbon (carbon and hydrogen based substance) and oxygen gas (O2)
We know it as either a fire or an explosion
The product will always produce CO2 and H2O
If the reactant has sulphur, it will produce SO2 as an additional product
It also releases energy in the form of heat or light

16. Combustion Without any sulphur CxHy + O2 → CO2 + H2O With sulphur
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)
With sulphur
CxHyS + O2 → CO2 + H2O + SO2
C5H12S + 9O2 → 5CO2 + 6H2O + SO2

17. Combustion What to look for? How to predict the products?
A hydrocarbon reacting with oxygen gas
How to predict the products?
If the reactant contains no sulphur, the product is CO2 and H2O
If the reactant contains sulphur, add SO2 to the products

18. Note! When SO2 is formed, it will react with water in our atmosphere.
When this happens, it produces sulphurous acid H2SO3 or acid rain
SO2 is produced by our cars
It can choke you if you breathe it in as it replaces the oxygen in your lungs (happened before)

19. Page 118 for summary table of chemical reactions

20. Example - 1
Predict, complete, and balance the following reactions and classify them
Al + O2 →
NO2 →
Cl2 + CaBr2 →
HNO3 + Sr(OH)2 →
C4H8S + O2 →

21. Video

22. Practice
Page #65-67