1. Chemical Reactions
Unit 11
(Chapter 11)

2. Chemical Reactions A chemical reaction is a chemical change
Changes the way atoms are bonded to each other
Chemical reactions are described by chemical equations
Two types:
Word Equations
Chemical Equations

3. Word Equations Uses the names of the chemicals Reactants  Products
“Reactants YIELD Products”
Can have multiple of both, separated by a plus sign that means “and”
Ex) Potassium iodide + hydrogen peroxide  Iodine + water + oxygen

4. Chemical Equations The most common way to show chemical reactions
Shows the chemical formulas as symbols
Still has the reactants on the left, and products on the right
P + P  R + R
A “skeleton equation” is a chemical equation that doesn’t tell you how many of each reactant or product you have

5. Let’s all try making a skeleton equation
You are reacting pure iron and chlorine gas (Cl2) to make iron (III) chloride. Write the skeleton equation.

6. Try these.
Write the skeleton equation for reacting nitrogen gas (N2) with oxygen gas (O2) to form nitrogen dioxide (NO2).
Write the skeleton reaction that results when propane (C3H8) reacts with oxygen gas to form carbon dioxide and water.

7. Catalysts
Catalysts are a chemical that “helps” the reaction happen, but doesn’t actually react or get changed.
In a chemical equation, the catalyst is written on top of the arrow

8. Write another skeleton reaction
Write a reaction where water is broken down to form hydrogen gas (H2) and oxygen gas (O2). Sodium hydroxide is the catalyst.

9. Symbols we’ll use +  (s) (l) (g) (aq)
“and” between two products or reactants 
Yields
Reversible reaction
(s)
A solid
(l)
A liquid
(g)
A gas
(aq)
“Aqueous” solution (dissolved in water)
Uses heat to do the reaction.
Uses a catalyst (in this case, an iodide ion)
Symbols we’ll use
heat or Δ I-

10. Okay, one more practice skeleton equation
Liquid acetone (C3H6O) reacts with oxygen gas to form liquid water and carbon dioxide gas.

11. Balancing Chemical Equations
Skeleton equations just tell you WHAT chemicals are in a chemical reaction
Ex) H2O2  H2O + O2
But it is also important to know HOW MANY there are
A “balanced” chemical equation tells you what chemicals and how many there are in a chemical reaction.
The number of each chemical is called the “coefficient” and is put IN FRONT of the symbols
Ex) 2 H2O2  2 H2O + O2

12. Let’s take a set back…
If I tell you to make a bookshelf, what do you need?
What if you want to make a bookshelf and an end table?

13. Let’s take a set back… 5 shelves + 2 sides + 1back  1 bookshelf.
7 shelves + 2 sides + 1 drawer + 4 legs  1 bookshelf and 1 end table

14. How to balance equations
Remember the Law of Conservation of Matter?
Matter is not created or destroyed
So, there MUST be the EXACT SAME number of each element in the reactants as the products!
Use coefficients to make the number of elements equal on both sides.
Basically a balancing “game”.

15. Let’s try one or two Balance these reactions: Fe + O2  Fe2O3
CaS + H2O  Ca(OH)2 + H2S

16. Some “rules” and tips to help you balance
Start with 1 element in the reactants, and balance it with the number in the products.
Choose elements that are in only 1 of the products first, just to make it easier.
Then balance the one that is bonded to the first element in the reactant.
Then balance the one that is attached to that one (if there is one).
Polyatomic ions usually stay together, so can be treated like a single element, rather than more than 1.
Check to see if it stays together first.

17. Try this… React aluminum metal with oxygen to form aluminum oxide.
Barium chloride (aq) reacts with potassium sulfate (aq) reacts to form barium sulfate (s) plus potassium chloride (aq)

18. Balancing equations worksheet
General notes on the back, just to help.
Depends on what you mean by “help”, I guess.

19. The 5 Types of Chemical Reactions!
To put together
Combination (or Synthesis)
Breaking apart
Decomposition
One swap places with another
Single replacement
Two swap partners
Double Replacement
To break apart C-H
with O2
Combustion
The 5 Types of Chemical Reactions!

21. Combination (Synthesis) Reaction
Do not look directly at the flame!
2Mg + O2  2 MgO

22. Decomposition Reaction
2Hg(SCN)2 → 2HgS + CS2 + C3N4

23. Single Replacement https://www.youtube.com/watch?v=OxGjbHzxQSI
Fe + 2CuCl  2Cu + FeCl2

24. Double Replacement Reactions
K2CrO4 + 2AgNO3  Ag2CrO4 + 2KNO
2KI + Pb(NO3)2 = PbI2 + 2KNO3

25. Combustion Reaction
WHAT?!?
2 C3H6O + 9 O2  6 CO2 + 6 H2O

26. Predicting Products of Chemical Reactions.
Combination
Just combine the two element, balance charges if ionic.
Decomposition
Split the elements, make diatomic of HONClBrF
Single replacement
The pure element will replace one of the other elements, with a pure element (or ion) being alone.
Double replacement
The four elements (or ions) will switch places, with the charges balanced out.
Combustion
End with H2O and CO2 (sometimes CO)
CO2 will be equal to the C’s in reactants.

27. Let’s try these reactions…
Decomposition:
FeCl2 
Double replacement:
NaOH + H2SO4 
Single replacement
FeCl3 + Zn 

28. How about these?
Synthesis
Ca + O2 
Combustion 
C4H10 + O2 

29. Reactions in Aqueous Solutions
Aqueous means “in water”
Ions usually dissolve in water because ions are charged, and water is also slightly charged (polar)
The ions “separate” from each other
We can write the ions out as a “complete ionic equation” by showing them separated with their charge and how many you need.
Ex) BaCl2 (aq) + K2SO4 (aq)  BaSO4(s) + 2KCl (aq) could be re-written as:
Ba2+(aq) + 2 Cl-(aq) + 2 K+(aq) + SO42+(aq)  BaSO42+(s) + 2 K+ (aq) + 2Cl- (aq)

30. Ba2+(aq) + 2 Cl-(aq) + 2 K+(aq) + SO42+(aq)  BaSO42+(s) + 2 K+ (aq) + 2Cl- (aq)
See how the K and Cl don’t really do anything? They just stay as aqueous. We call them “spectator ions”.
The shorter way to write a reaction in an aqueous is called a “net ionic equation” by getting rid of the spectator ions.
From (original equation):
Ba2+(aq) + 2 Cl-(aq) + 2 K+(aq) + SO42+(aq)  BaSO42+(s) + 2 K+ (aq) + 2Cl- (aq)
To (net ionic equation):
Ba2+(aq) + SO42+(aq)  BaSO42+(s)

31. Let’s try one:
Write the complete ionic equation, spectator ions AND the net ionic equation for the following equation:
AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)
Complete ionic equation:
Spectator ions:
Net ionic equation:

32. How do we know if it becomes solid?
Follow the (basic) solubility rules:
The following are soluble
Salts of alkali metals (or NH4+) are usually soluble
Nitrates and chlorates are usually soluble
Sulfates except for Lead (II), Silver, Mercury (I), Alkaline Earth Metals (Group 2) except Magnesium
Chlorides except Silver, Lead (II), and Mercury (I)
The following are USUALLY not soluble:
Carbonates, phosphates, chromates, sulfides, and hydroxides (unless it’s alkali metals)

33. Do you need to memorize that?

34. So, let’s try one more, for “fun”
You are going to react lead (II) chlorate with sodium iodide in an aqueous solution.
Write a balanced equation, with states.
Which ions would become a solid?
Write the complete ionic equation.
What are the spectator ions?
What is the net ionic equation?