Dimensional Analysis: Unit Conversion and Temperature Scales - Prof. Andy R. Kidwell, Study notes of Chemistry

Download Dimensional Analysis: Unit Conversion and Temperature Scales - Prof. Andy R. Kidwell and more Study notes Chemistry in PDF only on Docsity! Dimensional Analysis Conversion of a given result from one system of units to another In science, we often use unit factors to convert to different units Some examples: 16 oz./1 lb. another orientation is 1 lb./16 oz. 1 in./2.54 cm an alternative orientation is 2.54 cm/1 in. These factors do not change the number (measurement) only the unit Things to remember when converting units: 1) Use unit factors that relate the given unit to the desired unit 2) Derive the orientation of the unit factor by looking at the given unit and the desired unit 3) Perform the mathematical operation necessary (make sure appropriate units cancel) 4) Check the sig. figs. and the units 5) Does the answer make sense? How many miles would you walk if you had to walk 10.0 km? You need to know: 1 km = 1000 m 1 m = 100 cm 1 in = 2.54 cm 5280 ft = 1 mile 12 in = 1 ft Temperature There are three commonly used scales: 1) Kelvin Both used commonly in science 2) Celsius (or Centigrade) 3) Fahrenheit More common in Engineering Two reminders: 1) When written or typed there is always a space between the number and its unit 2) For Celsius and Fahrenheit we write them as degree F (ºF) or degree C (ºC). For the Kelvin scale we write it as Kelvin (K), there is no degree to this scale. How do we convert between the three scales? 1) Kelvin ↔ Celsius TK = TC + 273.15 or TC = TK – 273.15 Why 273.15? This is the difference in the two zero points. 2) Fahrenheit ↔ Celsius These scales are related using water as the standard. The boiling (condensing) point of water in Fahrenheit is 212 ºF The boiling (condensing) point of water in Celsius is 100 ºC The melting (freezing) point of water in Fahrenheit is 32 ºF The melting (freezing) point of water in Celsius is 0 ºC