L9: Aqueous Solutions I

Sugar Dissolving in water

Is there a way to predict if a chemical reaction will take place when two or more chemicals are placed touching each other? If one of the products of a reaction is a solid, liquid, or gas, the reaction is likely to happen. If electrons are transferred between any of the atoms of the reactants and products, the reaction is likely to happen. When liquids (or gases) are mixed together, their molecules can move around freely and come into contact with other molecules. If a reaction can occur, it does, and different substances are formed. Atoms and molecules in a solid phase are limited in their movement to small vibrational movements. For two solids to react with one another, the reaction has to start between atoms that are touching. To speed up the reaction, solids are often dissolved in a solvent such as water. When dissolved, ionic compounds separate into their ions which move easily through the aqueous solution. Molecular substances break up into molecules that are surrounded by water molecules. This gives them the mobility to contact other molecules and react. In this lesson we will look at the forces that drive a reaction to occur and write equations that describe reactions in aqueous solutions.

The four driving forces that cause chemical reactions to proceed from reactants to products are:
1.      Formation of a solid
2.      Formation of water
3.      Transfer of electrons
4.      Formation of a gas

Objectives for Lesson 9

After completing this lesson, you will be able to:

  • List the factors that cause reactions to occur
  • Identify the solid that forms in a precipitation reaction 
  • Describe reactions in solutions by writing molecular, complete ionic, and net ionic equations
  • Explain the key characteristics of the reactions between strong acids and strong bases