## Chem – Introduction to Problem Solving

What sections should I know before attempting to learn this section?

How do you solve word problems in chemistry?

Perhaps the most fundamental problem that most students have in chemistry is the lack of problem solving and organizational skills. I can never overstate how crucial these skills are for doing well in chemistry (and in life). One of the few regrets in all my life is that I did not pick up these skills sooner. Here I will try to lay out as best I can how to think your way through problems to come up with a correct answer. Since word problems are the most common in chemistry and because many people have trouble with them, I will focus my problem solving teaching on them. Improving your problem solving skills will be an ongoing process in any chemistry class, but I will show you the first and most important steps in this section. Be sure to always analyze my demonstrated examples for future insight into problems solving techniques.

Step 1: Underline, highlight, or box the numbers and units in a word problem. Because our brains are not very good at organizing many things at once, we need to show it where it needs to focus the effort. (I know this seems trivial but trust me it helps)

Step 2: Rewrite the numbers and units and identify what they are. Identifying what they are can help you later relate them to formulas or key concepts. (I know this seems trivial but trust me it helps)

Step 3: Restate the question in a short and simple way to guide you to the goal of finishing the question. Again, like the second step, this can help you relate information you already have to formulas or key concepts. (I know this seems trivial but trust me it helps)

Now let us demonstrate this method with some examples.  Remember you do not need to answer the problem only organize it.  Highlight the numbers and units in the word problems below. Rewrite the numbers and units and identify what they are.  Restate the question in a short and simple way.

Examples:   VIDEO Problem Solving Examples 1.

Problem Solving Demonstrated Example 1If an object has mass of 26g and a volume of 55mL what would its density be?

Step 1:  highlight numbers and units

If an object has mass of 26g and a volume of 55mL what would its density be?

Step 2:  Rewrite numbers and units and identify

26g = mass

55mL = volume

Step 3:  Restate question in simple way

density = ?

Step 4

26g = mass

55mL = volume

density = ?

Problem Solving Demonstrated Example 2:  An increase of 37K would cause the volume to go from 4.0L to 4.8L. What was the original temperature?

Step 1:  highlight numbers and units

An increase of 37K would cause the volume to go from 4.0L to 4.8L. What was the original temperature?

Step 2:  Rewrite numbers and units and identify

37K = temperature

4.0L = volume

4.8L = volume

Step 3:  Restate question in simple way

original temperature = ?

Step 4

37K = temperature

4.0L = volume

4.8L = volume

original temperature = ?

PRACTICE PROBLEMS: Highlight the numbers and units in the word problems below. Rewrite the numbers and units and identify what they are.  Restate the question in a short and simple way.

1. An object that takes up a volume of 2L and has a mass of 70kg would be what density?

Answer: 2L = volume….70kg = mass….Density = ?

2. If you run a distance of 900m at a time of 380s, what is your speed?

Answer: 900m = distance….380s = time….Speed = ?

3. It takes 15s to fill a 0.7L balloon. What is the rate of air from the container?

Answer: 15s = time….0.7L = volume….Rate = ?

4. If a 20g block takes 60s to heat from 0K to 300K. How long will it take to heat a 38g block of the same substance from 0K to 400K?

Answer: 20g = mass….60s = time….0K = temperature….300K = temperature….38g = mass….0K = temperature….400K = temperature….Time = ?

5. By changing from 78K to 142K the volume increased by 182%. What is the final volume if the original volume was 2.3L?

Answer: 78K = temperature….142K = temperature….182% = percent….2.3L = volume….Final volume = ?

6. Even if the question makes no sense. Picking out 7kg from the hyperbole of a transvector can lead you to 3L in case they ask, what is the density?

Answer: 7kg = mass….3L = volume….Density = ?  