1. Chemical Reactions (Rxn)
Unit 5
Part 2

2. Chemical Rxns
When one or more substance changes into one or more NEW substance.
Reactants  Products
(original substance) (new substance)
always on left always on right

3. Example of chemical rxns:

4. Chemical reactions are written as equations
Equations must be balanced because of the Law of Conservation of Matter
Matter can not be created nor destroyed in any chemical reaction

5. Chemical Symbols + used to separate reactants and products
“ Yields” or “Produces”,
used to separate the reactants from the
products
+ used to separate reactants and products
from themselves
Reversible Rxn (products can revert back)
(s) or ( ) =solid state
( l ) =Liquid state
(g) or ( ) =gaseous state
(aq) = aqueous solution- a solid dissolved in a liquid
heat is added catalysts- speed up
MnO2 chemical is added w/o changing the rxn

6. Indicators of Chem. Rxns
Release a gas (bubbles or smoke)
Changes COLOR
Change in energy (∆H)
Exothermic Rxn- Releases Energy –
-∆H
Endothermic Rxn - Absorbs Energy +∆H
Formation of a Precipitate-
a solid that forms from 2 aqueous solutions

7. 6 Types of Chemical Rxns Combination/Synthesis Decomposition
Single Replacement
Double Replacement
Combustion
Neutralization

8. Combination/ Synthesis
2 or more reactants produce product
A + X  AX
A + X + Y  AXY
Ex: Iron rusting
Fe + O2  FeO2
(rust)

9. Decomposition 1 Reactant produces 2 or more products AX  A + X or
AXY  AX + Y
Ex: Decomposition
of water
H2O ELECTRICITY H2 + 02

10. Single Replacement Single element replaces another in a compound
AY + B  BY + A
Ex: Copper + Silver nitrate  silver + copper (II) nitrate

11. Double Replacement 2 Compounds react to form 2 new compounds
AX + BY  AY + BX
Ex: Pb(NO3)2 + KI
PbI2 + KNO3

12. Combustion
Hydrocarbon reacts with oxygen to produce carbon dioxide and water
CxHx + O2  CO2 + H20
Combustion reactions
release ENERGY: light,
heat, chemical energy
(ex: ATP)

13. Types of Decomposition
Carbonates
Metal carbonate  metal oxide + carbon dioxide
Ex: CaCO3(s)  CaO (s) + CO2 (g)
Hydroxides
Metal hydroxide  metal oxide + water
Ex: Ca(OH)2 (s)  CaO + H2O (g)
Chlorates
Metal chlorate  metal chloride + oxygen
Ex: NaClO3  NaCl + O2
Acids
Acids non-metal oxide + water
H2CO3 (aq)  CO2 (g) + H2O (l)

14. Neutralization
Special type of double replacement between an acid & a base
Acid + Base  Water + Salt
Ex: HCl + NaOH  H2O + NaCl