1. Unit 5: Chemical Equations & Reactions
Chapters 8 and 13

2. Chemical Reactions
Chemical reaction – process by which one or more substances change into different substance(s).
REACTANTS  PRODUCTS
Starting chemical(s)
Ending chemical(s)

3. FOUR INDICATIONS Temperature change (gets hot or cold)
Gas forms (bubbling or fizzing)
Formation of precipitate (solid that is made by the reaction of two solutions)
Color change

5. Chemical Equations
Chemical Equations – describe what is happening during a chemical reaction
Chemical equations can be written or formulas can be used.
Reactants on left, products on right (of arrow)
“+” means and
Use (s), (l), (g), or (aq) after formulas
“” means forms
**Aqueous means the chemical is dissolved in water (solution)

6. Formula Equations H2 (g) + O2 (g)  H2O (l)
Formula Equations – represents the reactants and products by their symbols and formulas.
H2 (g) + O2 (g)  H2O (l)
Reactants
Products

7. Counting Atoms in a Formula
Subscripts only apply to the element directly in front of the number.
HNO H, 1-N, 2-O
Subscripts outside of ( ) need to be multiplied by everything inside the ( ). (Distributive property)
Ca3(PO4) Ca, 2-P, 8-O
What if I put a coefficient in front of the formulas?
2Al(C2H3O2) Al C 18-H 12-O

8. Balancing
Why?
chemical reactions must obey the law of conservation of mass (matter)
Mass is conserved (stays the same) during any physical or chemical change
Matter is not created or destroyed

9. Balancing
How???
1. Count the atoms of each element on both sides of arrow
2. Use coefficients in front of the formulas to balance the atoms
3. NEVER change a subscript!
**no coefficient = understood as a one (1)
5H2O
Coefficient subscript

10. Balancing Example
_____H2 (g) + _____O2 (g)  _____H2O (l) ___CS2 + ___Cl2  ___CCl4 + ____S2Cl2

11. More Balancing Examples
____ N2 (g) + ____ H2 (g)  ____ NH3 (g)
___ Al(OH)3 + ___ PbBr2  ___ AlBr3 + ___ Pb(OH)2

12. Word and Formula Equations
Word Equations – Uses names of reactants and products in the reaction
Hydrogen + Oxygen  Water
Have to turn the names into chemical formulas in order to balance

13. Review Writing Formulas
Acids (always start off with H)
“hydro-” acids
H+ balanced by an anion (NO OXYGEN)
HCl – hydrochloric acid
“non-hydro” acids
H+ balanced by negative polyatomic ion
“-ic acids” were “-ate ions” H2SO4 – sulfuric acid
“-ous acids” were “-ite ions” HNO2 – nitrous acid

14. Review Writing Formulas
Binary Covalent compounds (two nonmetals)
Numeric prefixes are subscripts…DO NOT BALANCE CHARGES!!!
Mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca
Sulfur hexafluoride – SF6 dinitrogen monoxide – N2O

15. Review Writing Formulas
Ionic compounds (+ and – charges need to be balanced)
Metal + nonmetal or metal + polyatomic ion
Look up charges and balance…positive and negatives add up to ZERO!
Sodium oxide Na+ and O2-  Na2O
Calcium phosphate Ca2+ and PO43-  Ca3(PO4)2
Iron (II) carbonate Fe2+ and CO32-  FeCO3

16. Correct symbols MEMORIZE THESE 7 DIATOMIC MOLECULES!! Hydrogen - H2
Oxygen - O2
Nitrogen - N2
Fluorine - F2
Chlorine - Cl2
Bromine - Br2
Iodine - I2
“7-up” or “I brought clay for our new house”

17. Writing Equations Examples
Solid magnesium reacts with hydrochloric acid to produce hydrogen gas and magnesium chloride solution.
Copper (II) sulfate solution reacts with sodium hydroxide solution to form solid copper (II) hydroxide and a solution of sodium sulfate.

18. Chemical Reactions
Law of Conservation of Mass MUST be obeyed…so equations must be balanced
total mass of the reactants must = total mass of the products

19. Types of Chemical Reactions
FIVE TYPES OF REACTIONS: Combustion Synthesis Decomposition Single Displacement Double Displacement

20. COMBUSTION Hydrocarbon (CxHy) reacting with O2 to form CO2 and H2O
Burning - Gives off heat and light!!
Basic format of reaction:
CxHy + O2  CO2 + H2O
EXAMPLE: CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O(l)

21. SYNTHESIS Two or more chemicals react to form A SINGLE NEW SUBSTANCE
i.d. HINT = A + B  AB
2K(g) + Cl2(g)  2KCl(s)

22. **you have to know your 7 diatomic molecules (7-up)
DECOMPOSITION
A SINGLE COMPOUND BREAKS DOWN into two or more simpler products.
i.d. HINT = AB  A + B
2HgO(s)  2Hg(l) + O2(g)
2HBr  H2 + Br2
**you have to know your 7 diatomic molecules (7-up)

23. Synthesis & Decomposition

24. SINGLE-DISPLACEMENT
An element replaces another element that is in a compound
i.d. HINT: A + BY  B + AY
Zn + Cu(NO3)2  Cu + Zn(NO3)2
Cl KI  I KCl

25. Single Displacement

26. DOUBLE-DISPLACEMENT LiOH + HCl  H2O + LiCl
Two different ionic compounds (in solution) mix to form two new ionic compounds.
Produces a precipitate (solid), gas (bubbles), or molecular compound (like water)
i.d. HINT: AX + BY  AY + BX
LiOH + HCl  H2O + LiCl

27. Double Displacement

28. Single Displacement continued
Metals replace metals (activity series)
List of metals
A metal can only replace another if it is ABOVE it on the series
K + CuCl2 
Cu + KCl 

29. Single Displacement continued
Halogens can replace other halogens
Fluorine is most active, can replace any halogen
Iodine is least active and can replace nothing, but can be replaced by everything.
F2 + 2NaBr 
I2 + NaCl 
Most reactive
Least
reactive

30. Solubility
Solubility: the ability of a substance to dissolve in another substance
Soluble means stays in solution = (aq)
Insoluble means forms a precipitate = (s)

31. Double Displacement Switch the positive ions in the compounds
Check solubility rules for precipitate (insoluble)
Re-balance charges
Balance equation
Pb(NO3)2 + KI 
NaCl + AlI3 