Chemistry word problems sometimes may be difficult. There are several methods for solving chemical word problems. A powerful technique for solving problems is called **unit analysis method**, sometimes referred to as **dimensional analysis method**, or **factor label method** of problem solving. Unit analysis cannot solve every chemistry word problem, but it is very effective for the problems we encounter in begining and college chemistry.

Insurance statistics state that a person loses 8 minutes of average life for each cigarette smoked. If there are 20 cigarettes in a pack and the average cost of cigarette is $4.50 per pack over the next 25 years, **how many** **years of average life** would a person lose for smoking 0.5 packs a day for **25 years**? How much would the person spend?

- Analyize the dimension of the unknown:
**years**_{lost} -
**years**is a_{lost}**single dimensio**n of time. Dimensions include:*Single***length**,**mass**,**time**,**count**, Alsoincludes*Simple***temperature**- Although
**volume**is**(length)**and not a single dimension, treat^{3}**volume**in chemistry as adimension*Simple* Dimensions include:*Compound***Density**:**Mass**/unit**Volume***g/mL*

Density_{tin}= 7.43 g_{Sn}/ 1 cm^{3}_{Sn}**Velocity**:**Length**/unit**Time***mi/hr*

Velocity = 55 mi / 1 hr;**Molecular Mass**:**Mass**/unit**Count***g/mol*

Molar Mass= 44.0 g_{CO2}/ 1 mol_{CO2}_{CO2}

**Mole Ratio**from balanced Equation: x Count/ y Count_{A}_{B}

Balanced Equation: 2A + 3B ---> 4C + 1D

Sample Mole Ratio of A to B: 2 mole/ 3 mole_{A}_{B}

**Molarity**: Count/ unit Volume_{solute}mol/L_{solution}

mole/ Liter_{solute}_{solution}

**%**_{by weight}: parts_{pure}/ 100 parts_{mixture}

Bleach = 5%_{NaClO}= 5 g_{NaClO solute}/ 100 g_{NaClO solution}- d. Note the labels placed on each unit. Labels must match before cancelling.
- The
**Given Unit**must have the same number of dimensions as the Unit of the Unknown. In the above problem**years**is time and only has one dimension. After the verb:_{lost}**"**is a unit factor:*would a person lose*"which can*0.5 packs a day***not**be the GIVEN since it is a compund dimension. The Given is:**= 25 years**another single/simple dimension_{smoking}

translates to:*'8 minutes of average life for each cigarette smoked'*

**8 min**_{lost}=1 cigtranslates to:*'20 cigarettes in a pack'*

**20 cig = 1 pack**translates to:*the average cost of cigarette is $4.50 per pack over the next 25 years*

**4.50 dollars**_{average}= 1 packtranslates to:*a person lose for smoking 0.5 packs a day*

**0.5 packs = 1 day**_{smoking}

- 365 days = 1 year
- 1 day = 24 hours
- 1 Hour = 60 minutes

VI. Apply a unit factor to convert the unit in the given value to the unit in the answer. If it can not be done with one unit factor, apply as many as needed to juggles the word (unit) of the given into the word (unit) of the unknown.

Decide how many unit factors must be applied to maske the conversion then connect to one of the following web pages to actually step up and calculate the answer:

- 1 unit Factor Needed
- 2 unit Factors Needed
- 3 unit Factors Needed
- 4 unit Factors Needed
- 5 unit Factors Needed
- 6 unit Factors Needed

- 5 unit Factors Needed

For the above problem, the following steps are performed into Single Unit Calculator with 6 unit factors.: