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Measurement and Units Study Guide (page 2)

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Updated on Sep 24, 2011

Dimensional Analysis (Factor-Label Method)

Dimensional analysis is the method to convert a number from one unit to another using a conversion factor. Conversion factors establish a relationship of equivalence in measurements between two different units. Examples of conversion factors are tabulated in Table 3.1 (metric prefixes) and Table 3.3 (common conversion factors).

Within the metric system, the prefix relationship is used (see Table 3.3). It is expressed as a fraction. For instance, for 1 kg = 2.2 lb., the conversion factor is 1 kg/2.2 lb. or 2.2 lb./1 kg.

Table 3.3 Common Conversion Factors

Convert From to Solution
185 lbs. kg 185 lbs. * = 83.9 kg
4.0 ft. cm 4.0 ft.* = 120 cm
235 mL qt. 235 mL * = 0.249 qt.
256 kB GB 256 kB * = 2.56 * 10–4GB
    (B is a byte)
2 ft., 3.5 in.m 2'3" = 27.5 in.*
    = .699 m

Temperature

Temperature is the measure of thermal energy (the total energy of all the atoms and molecules) of a system. The SI unit for temperature is Kelvin, but most scientific thermometers use the centigrade (Celsius) scale. However, most are more familiar with the Fahrenheit scale. Because many chemical calculations require Kelvin temperature, scientists frequently convert from degrees Celsius to Kelvin and from Kelvin to degrees Celsius.

°F to °C: °C = (°F – 32)

°C to °F: °F = °C + 32

K to °C: °C = K – 273.15

°C to K: K = °C + 273.15

Example:

Room temperature is 70° F. What is 70° F in Celsius and Kelvin scales?

Solution:

°C = (°F – 32)= (70 – 32) = 21.11 = 21° C

K = °C + 273.15 = 21.11 + 273.15 = 294.26 = 294 K

 

Practice problems for these concepts can be found at -  Measurement and Units Practice Questions

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