1. Word problems
2. Techniques for problem solving
3. Conversion factors
4. True Relationships [Practice Them ] [Practice Unit Cancelling] [Reference ]
5. Converting between units
6. Multistep problem solving
7. Converting complex units

Chapter 3

3-1 Word Problems

- Word problems are prevalent in chemistry.

3-2 Techniques of Problem Solving

- Remember to UNPAC:

 - Isolate the Unknown. ("What do I need to find out?")

 - Gather what is kNown or given. ("What information do I already have?")

 - Find a Path; this could be an equation or a relationsip, among other things. ("How am I going to use what I know to solve the problem?")

 - Do the A rithmetic. (If applicable.)

 - Complete and Check. This involves rewriting the answer, including units, and checking over your work.

3-3 Conversion Factors

- We can express values in chemistry with a variety of units. We can also convert between different units using conversion factors such as 4 quarters = 1 dollar or 100 centimeters = 1 meter.

3-4 True Relationships [Practice Them] [ Practice Unit Cancelling] [Reference]

- True relationships (AKA dimensional analysis) is a valuable way of solving problems. Here is an example of solving a problem using true relationships:

 - Hank is the chairperson of the International Lovers of Anchovies Club (ILAC). He is planning the eighth annual Anchovie Symposium and wants to  know exactly how many anchovies each attendee will get, so that he can put the number in the brochure. He wants to give each person 1 case. He  knows each case holds 30 bags of anchovies and that each bag contains 18 pounds of the delicacy. From years of experience, he knows that an  average of 12.5 anchovies go into every pound. So he sets up true relationships:

 4 People  x  1 Case Anchovies   x   30 bags anchovies  x  18 pounds anchovies   x     12.5 anchovies     = ?
        1                   1 person                 1 case anchovies            1 bag anchovies         1 pound anchovies

 At this point, Hank doesn't even know the units of the final answer. So to find out, he does some unit cancelling:

 4 People  x  1 Case   x   30 bags   x  18 pounds  x     12.5      =  ? anchovies
        1          1 person       1 case            1 bag         1 pound                  1

 As we know from math, anything over 1 is itself. So the answer is going to be a number of anchovies. Now he does the the math:

 4 x 1 x 30 x 18 x 12.5 anchovies   =  2700 anchovies

            1 x 1 x 1 x 1 x 1                                   1

 675 anchovies per person! Hank might want to rethink giving a whole case to every person.

3-5 Converting Between Units

- You can convert between units (like centimeters -> meters) using the True Relationships method described above in section 3-4.

3-6 Multistep Problems

- The example shown in section 3-4 is a multistep problem. More than one true relationship is needed to produce the answer.

3-7 Converting Complex Units

- The conversion of complex units (such as J/(g*K) - SpH) can be achieved using section 3-4's True Relationships method.

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