Patterns of Chemical Reactivity
Using the Periodic Table
• As a consequence of the good ordering of the periodic table, the properties of compounds of elements vary in a systematic manner.
• Example: All the alkali metals (M) react with water as follows:
2 M (s) + 2 H2O (l) --> 2 MOH (aq) + H2 (g)
The reactions become more vigorous as we move from Li to Cs
Sodium reacts with water to produce an orange flame.
Potassium reacts with water to produce a blue flame.
The reaction of potassium with water produces so much heat that the hydrogen gas produced usually ignites with a loud pop.
Combustion in Air
• Combustion reactions are rapid reactions that produce a flame.
Combustion is the burning of a substance in air.
Example: Propane combusts to produce carbon dioxide and water:
C3H8 (g) + 5 O2 (g) --> 3 CO2 (g) + 4 H2O (l)
Combination and Decomposition Reactions
• In combination reactions two or more substances react to form one product.
• Combination reactions have more reactants than products.
Consider the reaction:
2 Mg (s) + O2 (g) --> 2 MgO (s)
• Since there are fewer products than reactants, the Mg has combined with O2 to form MgO.
• Note that the structure of the reactants has changed:
Mg consists of closely packed atoms, and O2 consists of dispersed molecules.
MgO consists of a lattice of Mg2+ and O2- ions.
• In decomposition reactions one substance undergoes a reaction to produce two or more other substances.
• Decomposition reactions have more products than reactants.
Consider the reaction that occurs in an automobile air bag:
2 NaN3 (s) --> 2 Na (s) + 3 N2 (g)
Since there are more products than reactants, the sodium azide has decomposed into Na metal and N2 gas.
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About Me
- Gary Hi10spro Sakuma
- I have played for 25 years and coached for the last 17 years--certified United States Professional Tennis Association Professional One--worked for Punahou Schools-voted the #1 Sports School in the United States, as a Program Supervisor, in charge of coaching the High Performance Players as well as coordinating programs for K-12 and Tennis Pro Education.
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