1. Introduction to Chemistry
2. The Periodic Table
3. Quantum Numbers
4. Electron Configuration
5. Chemical Families
6. Oxidation Numbers
7. Chemical Formulas
8. Chemical Names
9. Formula Mass
10. Percentage Composition
11. Reaction Types
12. Balancing Equations
13. The Mole Concept
14. Solution Concentration
16. Kinetic Theory
17. The Gas Laws
18. Enthalpy & Heat
19. Reaction Rates
20. Acids & Bases
21. pH Scale
23. Net Ionic Equations
24. Redox Reactions
25. Organic Chemistry
26. Nuclear Chemistry
11. Types of Chemical Reactions
Chemical reactions are processes in which substances change into other substances.
You know a chemical reaction takes place if one or more of these occur:
- Color changes - Different combinations of molecules reflect light differently. A color change indicates a change in molecules.
- Heat content changes - In all chemical reactions, the heat content of the reactants and the heat content of the products is never the same. Sometimes the difference is great and can be easily detected. At other times, the difference is slight and more difficult to detect.
- Gas produced - Whenever a gaseous product forms in a liquid solution, bubbles can be seen. A colorless gas produced in a reaction of solids is much harder to detect.
- Precipitate forms - Precipitates are insoluble products formed by a reaction taking place in a liquid solution. This insoluble product will eventually settle to the bottom, but might immediately appear by turning the clear solution cloudy.
Most chemical reactions can be placed into one of five basic types:
1. Decomposition Reactions
- A compound breaks into parts.
- compound → element + element
- 2H2O → 2H2 + O2
Some decomposition complications with heat:
2. Synthesis Reactions
- Some acids, when heated, decompose into an acidic oxide and H2O.
H2SO3 → SO2 + H2O
- Metallic hydroxides, when heated, decompose into a metallic oxide and H2O.
Ca(OH)2 → CaO + H2O
- Metallic carbonates, when heated, decompose into a metallic oxide and CO2.
Li2CO3 → Li2O + CO2
- Metallic chlorates, when heated, decompose into metallic chlorides and O2.
2KClO3 → 2KCl + 3O2
- Elements are joined together.
- element + element → compound
- 2H2 + O2 → 2H2O
- Compounds are joined together
- compound + compound → compound
- 6CO2 + 6H2O → C6H12O6 + 6O2
3. Single Displacement Reactions
- A single element replaces an element in a compound.
- element + compound → element + compound
- Zn + 2HCl → H2 + ZnCl2
4. Double Displacement Reactions
- An element from each of two compounds switch places.
- compound + compound → compound + compound
- H2SO4 + 2NaOH → Na2SO4 + 2H2O
5. Combustion Reactions
The rusting of iron - 4Fe + 3O2 → 2Fe2O3
- A hydrocarbon (a compound containing only carbon and hydrogen) combines with oxygen.
- The products of combustion are always carbon dioxide and water.
- hydrocarbon + oxygen → carbon dioxide + water
- CH4 + 2O2 → CO2 + 2H2O
- When metallic substances combine with oxygen, the result is an oxidation-reduction reaction.
Chemical reactions can be classified in other ways as well:
Types of Reactions
- Special types of double displacement reactions that involve the reaction between an acid and base to form a salt and water.
- acid + base → salt + water
- Heat is usually given off in neutralization reactions.
- A suspension of solid magnesium hydroxide in water is widely used as an antacid to neutralize excess stomach acid:
Mg(OH)2 (s) + 2HCl (aq) → MgCl2 (aq) + 2H2O (l)
- Any reaction in which elements experience a change in oxidation number.
- one atom gains e&minus and another atom looses e&minus
S + O2 → SO2
- In the reaction above, sulfur and oxygen both have an oxidation number of zero before the reaction. After the reaction, sulfur is +4 and oxygen is −2.
- Aqueous reactions that involve the formation of a precipitate (solid).
- soluble compound + soluble compound → insoluble compound
2KI (aq) + Pb(NO3)2 (aq) → 2KNO3 (aq) + PbI2 (s)
- The physical state symbol (aq) says the reaction is taking place in a water solution. The physical state symbol (s) says the lead (II) iodide is a solid - therefore insoluble in the solution.
Predicting Reaction Products
Predicting Reaction Products