Ch400Ch4LN1 - Chem 400 Chapter 4 Lecture Notes Part 1...

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Chem 400 Chapter 4 Lecture Notes Part 1 Common Reaction Types • Why do chemical rxns occur? • One reason is that there is a “driving force” which forces reactants to react. • What are common driving forces for a rxn? • Formation of a solid (precipitate) • Formation of a gas • Formation of a weak electrolyte • Formation of water or another nonelectrolyte • There are several common types of reactions which we can describe in terms of a driving force. Precipitation Reactions : Reactions where a solid product is formed. This solid product “falls” out of the reaction solution (usually aqueous), or it precipitates. The formation of an insoluble solid is the driving force for the reaction. A very common type of precipitation reaction is a double displacement rxn (also called metathesis ), where 2 aqueous slns form an insoluble product and a soluble product. AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq) Acid-Base Neutralization Reactions : These are rxns where an acid and a base react together to form water and a salt. The formation of water is the driving force. Actually, if you look at these rxns closely, they are really a double displacement rxn. HNO 3 (aq) + NaOH(aq) H 2 O(l) + NaNO 3 (aq) Acid-Base Reactions : There is a more general type of acid/base rxn where an acid and a base react together to form a weak electrolyte, or a nonelectrolyte, or even a gas. The formation of the weak electrolyte, the nonelectrolyte, or a gas is the driving force. These are also double displacement rxns. Note that the base is an ionic salt. 2HNO 3 (aq) + Na 2 S (aq) H 2 S(g) + 2NaNO 3 (aq) HCl(aq) + NaCH 3 CO 2 (aq) CH 3 CO 2 H(aq) + NaCl(aq) Oxidation-Reduction Rxns : These are rxns, also called redox exns, where electrons are transferred between the reactants. Since electrons are electrical energy, this transfer of electrical energy is the driving force. Many common rxns are examples of redox rxns including
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Ch400Ch4LN1 - Chem 400 Chapter 4 Lecture Notes Part 1...

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