1. Chemical Equations and Reactions
Notes
Chemical Equations and Reactions

2. Chemical Equation Reactants: original substances
Products: new or resulting substances
Chemical Equation: represents, with symbols & formulas, the identities & relative amounts of the reactants & products in a chemical reaction

3. Evidence of a Chemical Reaction
Evolution of heat & light
Some give off light only or heat only
Production of a gas
Bubbles in a solution
Formation of a precipitate
A solid that is produced as a result of a chemical reaction in solution and that separated from the solution

4. Characteristics of Equations
Must represent known facts
All reactants & products must be included
Must contain correct formulas
Some elements when uncombined (elemental form) are diatomic H2, N2, O2, F2, Cl2, Br2, I2
Must always write their formulas this way!
Must satisfy law of conservation of mass
Atoms are not created or destroyed
Coefficients are added in front of formula as needed.

5. Word & Formula Equations
Word equation: reactants and products in a reaction are represented by words
Only has qualitative (descriptive) meaning
Formula equation: represents the reactants and products by their symbols or formulas
Must be balanced to satisfy law of conservation of massmore on this later!

6. Symbols Used in Equations
“yields” indicates results
used to indicate a reversible reaction
(s) indicates solid state; precipitate
alternate to (s) but only for precipitate
(l) indicates liquid state
(aq) substance dissolved in water
(g) indicates gaseous state
alternate to (g) but only for products

7. More Symbols Used in Equations
D heat reactants are heated
2 atm pressure at which reaction is carried out; 2 atm in this case
pressure pressure of reaction is greater than atmospheric pressure
0oC temperature at which reaction is carried out; 0oC in this case
MnO formula of catalyst used to alter rate of reaction; MnO2 in this case

8. Practice Convert word equation to formula equation
Methane gas and oxygen gas react to yield carbon dioxide gas and water vapor
Convert formula equation to word equation
2HgO (s) D Hg (l) + O2 (g)

9.   Synthesis
A synthesis reaction involves two or more substances combining to make a more complex substance.  The reactants may be elements or compounds, and the product will always be a compound.
A  +   B ---->  AB
element or compound + element or compound -----> compound
Examples
2H2(g) + O2(g) ----> 2H2O(g)
C(s) + O2(g) ----> CO2(g)
CaO(s) + H2O(l) ----> Ca(OH)2(s)

10. Synthesis (Composition) Reactions
Two or more substances combine to form a
new compound.
A + X  AX
Reaction of elements with oxygen and sulfur
Reactions of metals with Halogens
Synthesis Reactions with Oxides
There are others not covered here!

11. Three types of Synthesis
Elements react w/ O or S
Produces a metal oxide or metal sulfide
Also can produce nonmetal oxide
Metals react w/ halogens
Produces a metal halide compound
Oxides react w/ H2O
Metal oxides produce metal hydroxide
Nonmetal oxides produce oxyacids

12. Decomposition
In a decomposition reaction, one substance is broken down into two or more, simpler substances. 
AB ----> A  +  B
Compound > element or compound + element or compound
Examples
C12H22O11(s) ----> 12C(s) + 11H2O(g)
Pb(OH)2(cr) ----> PbO(cr) + H2O(g)
2Ag2O(cr) ----> 4Ag(cr) + O2(g)

13. Decomposition Reactions
A single compound undergoes a reaction that
produces two or more simpler substances
AX  A + X
Decomposition of:
Binary compounds H2O(l )  2H2(g) + O2(g)
Metal carbonates CaCO3(s)  CaO(s) + CO2(g)
Metal hydroxides Ca(OH)2(s)  CaO(s) + H2O(g)
Metal chlorates 2KClO3(s)  2KCl(s) + 3O2(g)
Oxyacids H2CO3(aq)  CO2(g) + H2O(l )

14. Five types of Decomposition
All usually require heat
Electrolysis:decomposition of a substance by an electric current
Binary Compounds
Produces elements
Metal Carbonates
Produces metal oxide & CO2
Metal Hydroxides
Produces metal oxide & H2O
Metal Chlorates
Produces metal chloride & O2
Acids
Produces nonmetal oxide & H2O

15. Single Replacement
In this type of reaction, a neutral element becomes an ion as it replaces another ion in a compound.  
Positive ion being replaced:  A + BC ----> B + AC
Negative ion being replaced:  A + BC ----> C + BA
element + compound ----> element + compound
Examples
Zn(s) + H2SO4(aq) ----> ZnSO4(aq) + H2(g)
2Al(s) + 3CuCl2(aq) ---> 2AlCl3(aq) + 3Cu(s)
Cl2(g) + KBr(aq) ----> KCl(aq) + Br2(l)

16. Single Replacement Reactions
A + BX  AX + B
BX + Y  BY + X
Replacement of:
Metals by another metal
Hydrogen in water by a metal
Hydrogen in an acid by a metal
Halogens by more active halogens

17. Four types of Single Replacement
Replacement of a metal by another metal
A more active metal will replace a less active metal
Replacement of hydrogen in water by a metal
Only most active metals (Group 1)
Produces metal hydroxide & H2
Replacement of hydrogen in an acid by a metal
Produces a salt & H2
Replacement of halogens
A more active halogen will replace a less active halogen
Activity decreases down group

18. The Activity Series of the Metals
Lithium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Zinc
Chromium
Iron
Nickel
Lead
Hydrogen
Bismuth
Copper
Mercury
Silver
Platinum
Gold
Metals can replace other metals
provided that they are above the
metal that they are trying to
replace.
Metals above hydrogen can
replace hydrogen in acids.
Metals from sodium upward can
replace hydrogen in water

19. The Activity Series of the Halogens
Fluorine
Chlorine
Bromine
Iodine
Halogens can replace other
halogens in compounds, provided
that they are above the halogen
that they are trying to replace.
2NaCl(s) + F2(g) 
2NaF(s) + Cl2(g)
???
MgCl2(s) + Br2(g) 
No Reaction
???

20. Double Replacement
Like dancing couples, the compounds in this type of reaction exchange partners. 
AB + CD ----> CB + AD
Compound + Compound ----> Compound + Compound
Examples
AgNO3(aq) + NaCl(aq) ----> AgCl(s) + NaNO3(aq)
ZnBr2(aq) + 2AgNO3(aq) ----> Zn(NO3)2(aq) + 2AgBr(cr)
H2SO4(aq) + 2NaOH(aq) ----> Na2SO4(aq) + 2H2O(l)

21. Double Replacement Reactions
The ions of two compounds exchange places in an
aqueous solution to form two new compounds.
AX + BY  AY + BX
One of the compounds formed is usually a
precipitate, an insoluble gas that bubbles out of
solution, or a molecular compound, usually water.

22. Three types of Double Replacement
Formation of a Precipitate
One product is solid & the other aqueous
Formation of a Gas
One product is gas & the other aqueous
Formation of Water
Acid-base neutralization is double replacement
H+ & OH- give water

23. Combustion
When organic compounds like propane are burned, they react with the oxygen in the air to form carbon dioxide and water. Combustion reactions will stop when all available oxygen is used up because oxygen is one of the reactants.
hydrocarbon + oxygen ----> carbon dioxide + water
Examples
CH4(g) + 2O2(g) ----> 2H2O(g) + CO2(g)
2C2H6(g) + 7O2(g) ----> 6H20(g) + 4CO2(g)
C3H8(g) + 5O2(g) ----> 4H2O(g) + 3CO2(g)

24. Combustion Reactions
A substance combines with oxygen, releasing a large
amount of energy in the form of light and heat.
Reactive elements combine with oxygen
P4(s) + 5O2(g)  P4O10(s)
(This is also a synthesis reaction)
The burning of natural gas, wood, gasoline
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)

25. Steps to Balancing a Chemical Equation
1 ) Write all reactants on the left and all products on the right side of the equation arrow. Make sure you write the correct formula for each element.
2) Use coefficients in front of each formula to balance the number of atoms on each side.

26. Steps to Balancing a Chemical Equation
3 ) Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list the number of atoms of each element on each side.

27. Steps to Balancing a Chemical Equation
4) It is often easiest to start balancing with an element that appears only once on each side of the arrow. These elements must have the same coefficient.
5) Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.
***Note**
It helps to balance hydrogen and oxygen last.