Introduction to Chemistry

1.3 Dimensional Analysis

and Conversions

Temperature• Temperature - It measures the average

kinetic energy of the atoms or molecules.

• Absolute zero – 0 Kelvin and is the point at which all molecular motion ceases.

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Temperature

• Kelvin is the standard

• Celsius°C = K – 273

• Fahrenheit

325

9 CF

Temperature Conversions• Convert 100 ˚C to Kelvin

• Convert 0 F to ˚C

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Given, Find, Process & Solve - GFPSProblem solving is an important skill in Chemistry. Have a procedure to

attack a problem is critical.

• Given-After identifying the problem, you need to organize all the information that is given to you. There are a lot of instances in chemistry where a given is not listed but you should know.

• Find-You need to know what you are solving for. So “what are you trying to find?” is the question you must always ask.

• Process-The process could be a conversion, stoichiometry or an equation. Your understanding of concepts can really guide the process.

• Solve-Try the process. If it doesn’t work, try a different process.

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Dimensional Analysis• Use conversion factors to change the units• Conversion factors = 1• 1 foot = 12 inches (equivalence statement)

• 2 conversion factors• Choose the conversion that will cancel the unit you need to

get rid of.

foot 1

inches 121

inches 12

foot 1

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7

Dimensional Analysis

Proper use of “unit factors” leads to Proper use of “unit factors” leads to proper units in your answer.proper units in your answer.

kilometer 1

mile 0.621371

mile 0.62137

kilometer 1 OK!

kilometer 0.62137

mile 11

mile 0.62137

kilometer 1 OK!Not

Dimensional AnalysisUnits with Powers

• Squared and cubed units are more complicated

3m 1 OK!

3m 1 OK!Not

Metric System

Base Quantity Name of Unit Symbol

Mass Kilogram kg

Length Meter m

Time Second s

Amount of Substance Mole mol

Temperature Kelvin K

SI Units

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Metric System - Prefixes

Prefix Symbol Meaning

Giga G 109

Mega M 106

Kilo k 103

Deci d 10-1

Centi c 10-2

Milli m 10-3

Micro µ 10-6

Nano n 10-9

Prefixes

• You must know these prefixes– kilo k 1000 times– deci d 1/10– centi c 1/100– milli m 1/1000

• kilometer - about 0.6 miles• centimeter - less than half an inch• millimeter - the width of a paper clip wire

Converting Metric Numbers• Converting metric will use dimensional analysis• Remember:

Large number small label = small number large label

• Make conversions that are easy to avoid mistakes– First convert the prefix to base– Second convert the base to the new prefix

• Convert 15 km to mm

Convert:

• 17 cg to kg

• 0.321 kL to mL

• 52 cm3 to L

• For more conversion help see metric tutorial

Example 1• The Kentucky Derby race is 1.25 miles. How long is the

race in km? 1 m = 1.09 yd

Example 2• A park in Irvine is 1.00 mile2. How many cm2 it is?

1.09 yard = 1 m

Example 3• A car travels 33 m/s what is its speed in mph?

1.09 yd = 1 m

Percent Error

• Data from experiments will often differ from accepted values.

• To express accuracy use percentage error

Percent Error = 100 x(Experimental Value - Actual Value)

Actual Value