1. Chemical Reactions

2. Using Everyday Equations
Every minute of the day chemical reactions are taking place both in and around you.
What makes something a chemical reaction?
A chemical reaction involves one or more substances,
the reactants, changing into one or more substances,
the products.
Reactants
Products
“ ” means “yields” or “reacts to produce.”

3. Chemical reactions can be described many ways
Chemical reactions can be described many ways. One is by using a word equation.
A word equation is an equation where reactants and products are represented by words.
Example:
methane + oxygen
carbon dioxide + water
Word equations, while useful, are cumbersome. To better describe a reaction, writing the formulas is used.
A chemical equation uses formulas of reactants (on the left) separated by an arrow from products (on the right).

4. Example:
Fe + O2
Fe2O3
(Skeleton equation)
- does not indicate the relative amounts of reactants and products
Most often symbols are used to describe the state (i.e., gas, solid, etc.) of each substance

5. Types of Reactions
The four types of chemical reactions we will talk about are:
Synthesis reactions
Decomposition reactions
Single displacement reactions
Double displacement reactions
You need to be able to identify the type of reaction and predict the product(s)

6. Steps to Writing Reactions
Some steps for doing reactions
Identify the type of reaction
Predict the product(s) using the type of reaction as a model
Balance it
Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as an element.
In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

7. 1. Synthesis reactions
Synthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.)
reactant + reactant  1 product
Basically: A + B  AB
Example: 2H2 + O2  2H2O
Example: C + O2  CO2

8. 2. Decomposition Reactions
Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds
1 Reactant  Product + Product
In general: AB  A + B
Example: 2 H2O  2H2 + O2
Example: 2 HgO  2Hg + O2

9. 3. Single Displacement Reactions
Single Replacement Reactions occur when one element replaces another in a compound.
A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-).
element + compound product + product
A + BC  AC + B (if A is a metal) OR
A + BC  BA + C (if A is a nonmetal)
(remember the cation always goes first!)
When H2O splits into ions, it splits into
H+ and OH- (not H+ and O-2 !!)

10. We have looked at several reactions: Fe + CuSO4  Cu + Fe2(SO4)3
Li + H2O  LiOH + H2
Such experiments reveal trends. The activity series ranks the relative reactivity of metals.
It allows us to predict if certain chemicals will undergo single displacement reactions when mixed: metals near the top are most reactive and will displacing metals near the bottom.
Q: Which of these will react?
Fe + CuSO4 
Ni + NaCl 
Li + ZnCO3 
Al + CuCl2  K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au
No, Ni is below Na
Yes, Li is above Zn
Yes, Al is above Cu
Yes, Fe is above Cu
Cu + Fe2(SO4)3
NR (no reaction)
Zn + Li2CO3
Cu + AlCl3

11. A: No for cold, yes if it is hot/steam Mg + H2O  H2 + Mg(OH)2 acid
H is the only nonmetal listed. H2 may be displaced from acids or can be given off when a metal reacts with H2O (producing H2 + metal hydroxide). The reaction with H2O depends on metal reactivity & water temp.
Q: will Mg react with H2O? K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au
cold H2O
hot H2O
steam
A: No for cold, yes if it is hot/steam
Mg + H2O 
H2 + Mg(OH)2
acid
Q: Zn + HCl 
H2 + ZnCl2
Complete these reactions:
Al + H2O(steam) 
Cu + H2O 
Ca + H2SO4 
Na + H2O 
H2 + Al(OH)3 NR
H2 + CaSO4
H2 + NaOH

12. Other Activity Series Information
All metals will have a specific place in the activity series. For simplicity, only the most common metals are shown.
The metals near the top of the activity series are more reactive because their valence electrons are more easily removed.
On tests and exams the activity series may appear as K, Na, … Ag, Au; you must remember that K is reactive, Au is not.
If the valence of a metal is not indicated in the question, use its most common valence (in bold on your periodic table) to determine the correct chemical formula.

13. 4. Double Displacement Reactions
Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound
Compound + compound  product + product
AB + CD  AD + CB

14. Double Displacement Reactions
Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together
Example:
AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq)
Another example:
K2SO4(aq) + Ba(NO3)2(aq)  KNO3(aq) + BaSO4(s) 2