1.13: SI Units
- Page ID
- 178203
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Base Units
The SI contains seven BASE UNITS that each represent a different kind of physical quantity. These are commonly used as a convention.
| PHYSICAL QUANTITY | NAME OF UNIT | ABBREVIATION |
|---|---|---|
| Mass | Kilogram | kg |
| Length | Meter | m |
| Time | Second | s |
| Temperature | Kelvin | K |
| Amount of Substance | Mole | mol |
| Electric Current | Ampere | A |
| Luminous Intensity | Candela | cd |
Derived Units
Derived Units are created by mathematical relationships between other Base Units and are expressed in a combination of fundamental and base quantities.
| DERIVED QUANTITY | NAME | ABBREVIATION |
|---|---|---|
| Area | Square Meter | m2 |
| Volume | Cubic Meter | m3 |
| Mass Density | Kilogram Per Cubic Meter | kg/m3 |
| Specific Volume | Cubic Meter Per Kilogram | m3/kg |
| Celsius Temperature | degree Celsius | oC |
Temperature
Temperature is usually measured in Celsius (although the U.S. still uses Fahrenheit), but is often converted to for the absolute Kelvin scale for many chemistry problems.
- For Fahrenheit to Celsius: \[F= \dfrac{9}{5} \times C+32 \nonumber \]
- For Celsius to Fahrenheit: \[C= \dfrac{5}{9} \times F - 32 \nonumber \]
- For Celsius to Kelvin: \[K=C+273.15 \nonumber \]
Reference Points:
- Melting Point of ice is 0° C = 32° F
- Boiling Point of water is 100° C = 212° F
The Kelvin scale does not use the degree symbol (°) and only K, which can only be positive since it is an absolute scale
Mass
Mass is usually measured by a sensitive balance machine
- 1 kilograms = 2.205 lbs.
- (Remember that 1 kg = 1000 grams)
Length
The U.S. usually makes measurements in inches and feet, but the SI system prefers meters as the unit for length.
- 1 meter = 3.281 feet.
- 1 inches = 2.54 centimeters
Volume
SI units commonly uses derived units for Volume such as meters cubed to liters.
- 1 cm3 (centimeter cubed) = 1 mL (mililiter)
- 1000 cm3 = 1 L = 1 dm3
Energy
- 1 calorie = 4.184 Joules
Amount of Substance
- 1 mole = 6.022 x 1023 molecules/atoms
- (Avogadro's number)
Problems
Convert to the appropriate SI Units:
- 1 Day 4 Hours and 20 Minutes
- 10.8 Lbs.
- 58.8 Ft.
- 10,288 grams
- 128,968,888 mL
- 1.4 Degrees Celcius
- 16.13 Cal
- 18,888,888 km
References
- Petrucci, Ralph H. General Chemistry. 9th ed. New Jersey: Pearson Prentice Hall, 2005.
- Ryamond, Kenneth W. General, Organic, & Biological Chemistry. 2nd Ed. Danvers, MA: John Wiley & Sons Inc., 2008.
Contributors and Attributions
- Christina Doan (UCD), Ryan Cheung (UCD)