There are thousands of ways that more than one hundred elements can combine with each other to form different substances. Just as the elements can be sorted into families, the many reactions the elements undergo can be classified as a few basic types. The types of reactions are classified based on whether they involve combining atoms or smaller molecules to make larger molecules (synthesis), breaking down larger molecules into atoms or smaller molecules (decomposition), or having atoms of one element replace the atoms of another element within a compound (single- or double-displacement).

Bellringer/6.2 Notes

1. In which reaction model do three elements combine to make a compound?

2. In which reaction model is a complex substance broken down into simpler parts?

3. Identify the reaction model in which one element reacts with a compound, leaving behind another element and a new compound containing the first element.

4. In which reaction model do two compounds react to form two different compounds?

I. Classifying chemical reactions

A. There are 100s of kinds of reactions. Most of these will fit into one of four categories

1. Synthesis reactions-two or more substances combine to form another substance.

A + B AB

2. Decomposition reaction-one substance breaks down or decomposes into two or more simpler substances.

AB A + B

3. Single displacement reaction-one element replaces another in a compound.

A + BC AC + B

OR

D + BC BD + C

4. Double displacement reaction-takes place when two compounds react forming two new substances

AB + CD AD + CB

a. A Precipitate (insoluble compound) will form

Symbol MeaningProduces or forms

(cr) Solid

(l) Liquid

(g) Gas

(aq) Aqueous, a solid is dissolved in water

heat The reactants are heated

light The reactants are exposed to light

elect. An electric current is applied to the reactants

Practice: Write each chemical reaction down and classify each reaction as single displacement, double displacement, decomposition, or synthesis.

1. H2O H2 + O2

2. CuCl + Al AlCl + Cu

3. Na + Cl2 NaCl

4. Pb(NO3)2 + K2CrO4 PbCrO4 +

KNO3

5. S8 + O2 SO2 + heat

6. CO2 + H2O C6H12O6 + O2

7. NaHCO3 Na2CO3 + H2O + CO2

8. Zn + HCl ZnCl2 + H2