Lacey_Che131_S2012_Lect-2s

Lacey_Che131_S2012_Lect-2s - Lec ‐ 2 Measurements and...

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Unformatted text preview: Lec ‐ 2: Measurements and units http://www.chemreview.net/SB.htm 1 Roy A. Lacey, Stony Brook University; Che 131, Springl 2012 Module ‐ #3 Measurements ` Accurate measurements are essential for characterizing UNITS MATTER!! the physical and chemical properties of matter. ` Standardization of the units Standardization of the units of measurements is of measurements is essential. essential. ` Quantitative Quantitative ‐ easy to check ` Easy to agree upon, no personal bias ` The measuring instrument limits how good th t i 2 Roy A. Lacey, Stony Brook University; Che 131, Springl 2012 the measurement is. SI Units Quantity Base Unit Abbrev. Symbol Length meter m l Mass Tim kilogram secon kg m Time Temp second Kelvin s K t T Amount mole mol n 3 Roy A. Lacey, Stony Brook University; Che 131, Springl 2012 Prefixes for SI units 4 Roy A. Lacey, Stony Brook University; Che 131, Springl 2012 Scientific Notation 9 A simple way of writing numbers that accommodates values too large or small to be conveniently written in standard decimal notation b Sign Exponential 10 b a × μ 2 321 3 21 10 → × 1 1 10 10 b b x a y a = × = × i i f i d 3 4000 4 10 → × 321 3.21 10 → × 6 5720000 5 72 10 → × 1 1 1 10 b b xy a a a x + = × significand 5720000 5.72 10 → × 6 0.0000075 7.5 10 − → × 1 1 10 b b a x y a − = × 5 Roy A. Lacey, Stony Brook University; Che 131, Springl 2012 For addition and subtraction make all of the exponents the same Derived units Quantity Name Symbol Area square meter m 2 Volume cubic meter m 3 Force newton N =kg.m/s 2 2 Pressure pascal Pa = 1N/m 2 Energy joule J = 1 Kg.m 2 /s 2 Power watt W = J/s Electric charge coulomb C Electric charge coulomb C Current ampere A = C/s Voltage volt V = W/A = J/C Frequency hert H Frequency hertz Hz 6 Roy A. Lacey, Stony Brook University; Che 131, Springl 2012 How good are the measurements? We use two words to describe how good measurements are ` Accuracy ‐ how close the measurement is to the actual value ` Precision ‐ how well can the measurement be repeated All scientific measurements are subject to error. 9 These errors are reflected in the number of figures reported for the measurement....
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This note was uploaded on 03/29/2012 for the course CHE 131 taught by Professor Kerber during the Spring '08 term at SUNY Stony Brook.

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Lacey_Che131_S2012_Lect-2s - Lec ‐ 2 Measurements and...

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