Lesson 3: Wrap-Up
In this lesson, we studied the stoichiometry of chemical reactions, that is, the relationships between the amounts of the various chemical reactants and products that are involved in chemical reactions.
We found that total mass was conserved in all chemical reactions. This follows from the fact that in chemical reactions, atoms are neither created nor destroyed. It is for this reason that we can balance chemical reactions by making sure that the total number of atoms of each element are the same among the reactants and products.
The balanced equation for a reaction therefore gives us all the information we need to determine the number of grams of any product formed or reactant consumed, given the number of grams of any other product formed or reactant consumed.
As we continue our study of chemistry, we will see what leads to this kind of regular and predictable behavior, and we will learn not only how to explain it, but how to make predictions of the formulas of compounds ourselves.
That brings us to the end of the lesson, except for the practice work. You should be sure to review this lesson, of course. Go back through the objectives, make sure that you can do each one. You should be in pretty good shape if you have been keeping up with everything as you went through. Also take the self-quiz for this lesson and check your answers.
For this lesson, you need to turn in the problem set and a record of your computer practice session. If you don't already have everything down pat, be sure to get lots of practice balancing equations and working on the problems. That's all for this lesson.
Self Quiz
1. The statement, "Two clear, colorless liquids were mixed together, and a white solid formed," describes a:
a. physical change
b. chemical change
2. When 15 g of ethane reacts with (burns in) oxygen, 27 g of water and 44 g of carbon dioxide are formed. How much oxygen is used?
a. cannot tell--need more information
b. 32 g
c. 56 g
d. 24 g
e. 9.0 g
3. If 22 g of carbon dioxide is formed by burning 6.0 g of carbon in air, how much oxygen is used when 18 g of carbon is burned in air?
a. 22 g
b. 48 g
c. 66 g
d. 6.0 g
e. 18 g
Use this equation to answer the following questions (#4-6):
2 Na + Cl2 --> 2 NaCl
4. How many moles of sodium will react with 1.2 moles of chlorine (Cl2)?
5. How many grams of sodium chloride (NaCl) can be made from 15 g of sodium?
6. How much chlorine would be necessary to react with 15 g of sodium?
7. The Law of Conservation of Mass says that:
a.For a specific compound, the weight of one element is always constant.
b.For a specific compound, the ratio of the weight of one element to the weight of another in the compound is always the same.
c.There is no change in mass in a chemical process.
d.None of the other answers.
e.All of the other answers (except none).
Categorize and balance the following equations:
8. C3H8 + O2 --> CO2 + H2O
9. Na2SO4 + BaCl2 --> NaCl + BaSO4
10. Fe + O2 --> Fe2O3
Self Quiz Answers
1. b
2. c
3. b (you need to use conservation of mass to find the amount of oxygen that reacts with the 6.0 g of carbon first, then use the conversion factor or proportion method to find the final answer)
4. 2.4 moles Na
5. 38 g NaCl (determine the weight relationships from the balanced equation; 45.98 g Na will produce 116.88 g NaCl)
6. 23 g (use the weight relationships from the balanced equation; 45.98 g Na will react with 70.90 g Cl2)
7. c
8. miscellaneous; coefficients = 1, 5, 3, 4
9. double replacement (or double displacement); coefficients = 1, 1, 2, 1
10. combination; coefficients = 4, 3, 2