Chapter 6
Exam Review

To study for this exam, you should:

a.  Go over this review sheet.
b.  Be familar with every experiment.  See textbook or web handouts.
c.  Go over all the problems in the book, consulting your notes if necessary.
d.  Practice balancing equations.

The experiments can be found in the book. You did every book problem already in class, and should have notes about each.  There are no redos for Chapter 6 exams so study hard!

The main subject in this chapter is the ideas of molecules and atoms, and the principle of constant proportions.

This chapter deals with chemical reactions as opposed to physical reactions.  A physical reaction changes a substance's state from a gas to a liquid or a solid.  A physical reaction can easily be reversed.  Dissolving is another example of a physical reaction.  But a chemical reaction changes the substance itself.  It is this fact that leads to the theory of atoms and molecules. 

A substance is made of molecules, the smallest little pieces of the substance.    If you separate molecules one from another, that is a physcial reaction, the more they move around the more you go from solid to liquid to gas. 

Each molecule is made of a fixed proportion of atoms.
  For example every water molecule is made up of two hydrogen atoms and one oxygen atom.  But if you bust up the molecules of a substance so that the atoms are no longer connected, you have a chemical reaction that changes the substance.  For example, busting up water molecules (H2O) makes Hydrogen and Oxygen.  

The Law of Constant Proportions

Throughout all the decomposition and synthesis experiments, we learned that fixed ratios of mass are used in building new substances, and the same is true when breaking those substances down.  For example, in the case of water, 1 gram of Hydrogen and 8 grams of Oxygen are used to make 9 grams of water.  The fixed ratio is true for volume as well, but because the density of most substances are different, the actual ratio of volume is different.  For example, for water the volume ratio of hydrogen to oxygen is 2 to 1, and the mass ratio is 1 to 8.

Chemical reactions sometimes require energy and sometimes give off energy.  For example, decomposing water requires energy, and synthezing water gives off energy.  In this chapter we separated and synthesized (put together or build a substance) a number of different substances to explore these ideas.  Sometimes (like for water) decomposition absorbs energy and synthesis gives off energy, and sometimes it works the other way. 

Balancing chemical equations is a tricky and challenging skill that makes sure that the total number of atoms in any reaction does not change.  Make sure you understand that 4H2O means 4 water molecules each of which has two hydrogens and one oxygen.  That makes 8 Hydrogen atoms and 4 Oxygen atoms.  Get used to that notation and you will have an easier time balancing equations.

Practice your skills here.

Some terminology and ideas you should know:








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