1. Chemical Reactions

2. State Standard
Standard 3- Interactions of Matter CLE 2- Analyze Chemical Reactions CLE 3- Explore Formulas and Equations CLE 4- Explain the Law of Conservation of Mass/Energy SPI 2 – identify reactants, products, and types of reactions SPI 4 – balance chemical equations

3. Chemical Equations
Chemical equations are used to represent chemical reactions
writing the equation doesn’t make it so!
Equations can be written with words or with formulas
You should be able to interpret a formula equation with words, as well as write the formula equation from words

4. Substances initially present before reaction are called reactant(s)
Substances present after the reaction has occured are called product(s)
An arrow (→) separates the products and reactants

5. Symbols and Phase Labels
Symbols and phase labels are used to indicate the physical state of the reactants and products and conditions under which the rxn occurs
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous solution, dissolved in water
∆ / heat = heat added
catalyst formula = catalyst
temp/pressure = conditions of rxn

6. Describe the following chemical equation in words:
2H2O + O2  2H2O2

7. 2H2O + O2  2H2O2
Two molecules of water combine with one molecule of oxygen gas to form (yield) two molecules of hydrogen peroxide

8. Write an equation for the following:
Solid sodium metal combines with liquid water to yield aqueous sodium hydroxide and hydrogen gas.

9. Na(s) + H2O(l)  NaOH(aq) + H2(g)

10. Write this equation:
Solid sodium hydrogen carbonate and aqueous hydrochloric acid react in a beaker to produce aqueous sodium chloride, liquid water, and carbon dioxide gas.

11. NaHCO3(s) + HCl(aq)  NaCl(aq) + H2O(l) + CO2(g)

12. Balancing Chemical Equations
Coefficients are used in front of reactants and products in a chemical equation to balance the equation according to the Law of Conservation of Mass, which must be obeyed in all chemical processes
Formulae of reactants and products are never changed in order to balance an equation

13. Balancing Chemical Equations
How would you write an equation for making a bicycle?
Use these parts: frame (F)
wheels (W)
pedals(P)
handlebars (H)

14. Bicycle
F + 2W + 2P + H  FW2P2H
One frame, two wheels, two pedals, and one set of handlebars yields one bicycle (an FW2P2H)

15. Steps in Balancing An Equation
Fe3O H Fe H2O
Fe: Fe3O H Fe H2O
O: Fe3O H Fe H2O
H: Fe3O H Fe H2O

16. Balance these equations
H2 + O2  H2O
AgNO3 + H2S  Ag2S + HNO3
Zn(OH)2 + H3PO4  Zn3(PO4)2 + H2O

17. Balance these equations
2H2 + O2  2H2O
2AgNO3 + H2S  Ag2S + 2HNO3
3Zn(OH)2 + 2H3PO4  Zn3(PO4)2 +6H2O

18. Types of Reactions There are 5 major classes of reactions:
synthesis
decomposition
combustion
single replacement/displacement
double replacement/displacement
Classifying a reaction is often helpful in predicting products

19. How to Classify a Reaction
Look at reactants and products…
Synthesis: 2 or more substances combining to make 1 substance: 2 → 1
Decomposition: 1 substance breaking down into 2 or more substances: 1 → 2
Combustion: reaction with elemental O2
- we will only consider 1 type- hydrocarbon combustion
- complete combustion produces CO2 and H2O always, regardless of hydrocarbon

20. -*May involve acids and water, as well Single Replacement:
Double Replacement:
ionic*cmpd1 + ionic cmpd2 → ionic cmpd3 + ionic cmpd4
-*May involve acids and water, as well
Single Replacement:
element + cmpd → element + cmpd

21. Types of Reactions and Predicting Products

22. State Standard Standard 3- Interactions of Matter
CLE 2- Analyze Chemical Reactions
CLE 3- Explore Formulas and Equations
CLE 4- Explain the Law of Conservation of Mass/Energy
SPI 2 – identify reactants, products,
and types of reactions
SPI 3- predict products of reactions
SPI 4 – balance chemical equations

23. Synthesis Reactions
Two or more substances react to form a single new substance.
Reactants may be 2 elements or an element and a compound
2K(s) + Cl2(g)  2KCl(s)
Cmpd formed may be molecular or ionic
Follow rules for writing formulas of ionic cmpds
Give a reasonable formula for a molecular cmpd

24. Decomposition Reaction
A single compound breaks down into two or more simpler products.
Products may be 2 elements or an element and compound or 2 compounds
2HgO(s)  2Hg(l) + O2(g)
Most elements exist in elemental form as a monatomic atom
Exceptions: H2, N2, O2, F2, Cl2, Br2, I2, P4 and S8

25. Decomposition Products
Carbonates (compounds containing CO32–) give off carbon dioxide and leave oxide compounds behind. Sulfates (with SO42–) give off sulfur trioxide and leave oxide compounds behind. Hydroxides (with OH1–) produce water and leave oxide compounds behind. Chlorates (with ClO31–) give off oxygen and leave chloride compounds behind. Hydrates (with H2O) break up into water and anhydrous compounds. Binary compounds (made of just two elements) break down into their elements. (Don't forget about HOFBrINClSP!)

26. Combustion Reactions Burning reaction
An element or compound (hydrocarbon) reacts with oxygen (O2) and often produces heat and light.
CO2 and H2O are always the products of complete hydrocarbon combustion.
Incomplete combustion produces CO, rather than CO2
C8H18(l)+ O2(g) CO2(g)+H2O(l)

27. Single Replacement Reactions
3 types
*The activity series must be used to determine products for all types of SR rxns
1) A single metal displaces another metal from a compound to produce a new compound and a new single metal.
Fe(s) + Pb(NO3)2(aq)  Fe(NO3)2(aq) + Pb(s)
A metal can replace any metal below it on the activity series
Fe is above Pb on the activity series, so it can displace Pb from the compound
Nitrates are insoluble, so aq

28. 2) A metal displaces H from water or acid*
* be sure to read conditions for these
a) Pb(s) + H2O(l) → ? (NR)
- Pb displaces H from acids only, so this one is NR
b) Cr(s) + H2O(l) → ? (NR)
- Cr displaces H from steam- rxn doesn’t say temp. is above room temp., so no steam and NR
3) A halogen displaces another halogen from a compound
-Halogens go in same order as group: F (most reactive) → I (least reactive)
a) Br2 + NaCl→ ? (NR)
Br is below Cl, so NR
b) F2 + CaBr2 → ? (Br2 + CaF2)
- F is above Br, so Br2 + CaF2

29. Double Replacement Reactions
Cations and anions in 2 ionic compounds switch partners: inner 2 and outer 2-
3Ba(NO3)2 + 2H3PO4  Ba3(PO4)2 + 6HNO3
Subscripts do NOT carry from reactant side to product side- they are there to balance the ions in the formula to get the correct formula
Cation always first in formula!!
Order of product compounds doesn’t matter- either compound can come first

30. DR Reactions
DR reactions have conditions under which they will not occur…
There must be a driving force to make the reaction proceed otherwise there is no rxn-NR
Driving forces include:
evolution of gas
formation of a precipitate-solid
formation of a liquid (H2O only liquid we use)
formation of a WA/WB (not in this class)

31. Gas forming reactions must be learned
H2S(g), NH3(g), CO2(g), and SO2(g) are most common, but are hard to recognize as products…
NH4OH(aq) = NH3(g)+ H2O(l)
H2CO3(aq) = CO2(g) + H2O(l)
H2SO3(aq) = SO2(g)+ H2O(l)
Liquid forming , i.e. water, reactions are called acid- base reactions
Reaction of an acid (H-) with a base (-OH) will produce water and a salt (ionic compound)
HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)

32. Cont’d…
Precipitate reactions require the use of a solubility table (handout) to determine if a compound is aqueous in water (soluble) or will precipitate out (insoluble)
3Ba(NO3)2(aq) + 2H3PO4(aq)  Ba3(PO4)2(?) + 6HNO3(?)
You must check the products- no gas or liquid formed, so check solubility table for solid formation…
Generally check the anion- few rules involve cations
Phosphates- frequently insoluble → solids
Nitrates- generally soluble → aqueous
3Ba(NO3)2(aq) + 2H3PO4(aq)  Ba3(PO4)2(s) + 6HNO3(aq)

33. Net Ionic Equations Show only the ions participating in the reaction
The ions that do not participate are called spectator ions
Steps:
All (aq) compounds are broken apart into their respective ions; this is a better representation of aq compounds
Solids, liquids and gases are not broken apart
Ions that appear on both the reactant and product side are cancelled; these are the spectator ions
Coeff must match in order to cancel ions

34. Example: Ba(NO3)2(aq) + (NH4)2S(aq) → 2NH4NO3 (aq) + BaS(s)
Ba2+(aq) + 2NO3-(aq) + 2NH4+(aq) + S2-(aq) → 2NH4+(aq) + 2NO3-(aq) + BaS(s)
Ba2+(aq) + S2-(aq) → BaS(s)