Week 1 Notes
Week 1 Notes CHEM 105A
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This 3 page Class Notes was uploaded by Emma Morrissey on Saturday August 27, 2016. The Class Notes belongs to CHEM 105A at University of Southern California taught by Thomas Michael Bertolini in Fall 2016. Since its upload, it has received 42 views. For similar materials see General Chemistry in Chemistry at University of Southern California.
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Date Created: 08/27/16
Chapter 1 ● Law- a statement summarizing an event simply through observation. ○ There are no exceptions ○ No explanation ○ Few accepted scientific laws ● Theory- an attempt to explain why an event occurred ○ Not always correct ● Chemistry ○ The study of matter, its properties, and its interactions ○ Comprises of everything in the universe except for space in a vacuum ● Matter is anything that has mass and occupies space ● Types of matter ○ Solid: definite shape, definite volume, not compressible ○ Liquid: no definite shape, definite volume, not very compressible ○ Gas: no definite shape, no definite volume, compressible ○ Others: glass, plasma, liquid crystal, supercritical fluid ● Composition of matter ○ Pure substances have constant composition ■ Examples: ● Elements (can only be broken apart through nuclear reactions) ● Compounds (can only be broken down through chemical reactions) ○ Impure substances are mixtures of elements and/or compounds with other elements and/or compounds ■ Types of mixtures ● Homogeneous mixtures (aka solutions); salt water ● Heterogeneous mixtures; cereal ● Physical and chemical changes ○ Physical changes are simple changes in form or state ■ Melting, freezing, bending ○ Chemical changes occur when the substance changes ■ Different chemical composition; burning, change in color ● SI units ○ Meter (m) ○ Kilogram (kg) ○ Second (s) ○ Kelvin (K) ○ Moles (mol) ○ Ampere (A) ○ Candela (cd) ● About the Kilogram ○ The International Prototype Kilogram (IPK) in France is the kilogram ○ Cylinder roughly 39 mm in height made of platinum and iridium ● Temperature ○ Commonly measured in degrees Celsius, but when performing calculations, we must use Kelvin in order to avoid negative values and zero. ● Derived units ○ Combine base SI units ■ Volume ■ Density ● Significant Figures ○ Used to measure uncertainty; indicates precision in measurement ○ Includes all certain digits plus one uncertain (estimated) digit at the end ● Counting and using sig figs ○ Non-zero digits are always significant ■ 123456789 ○ Captive zeros are always significant ■ 404, 300000003, 2030401 ○ Leading zeros are never significant ■ 0000003, 0.0004, 0.1 ○ Trailing zeros are significant if there is a decimal place ■ 300 (No), 3.00 (Yes) ○ Exact numbers have an infinite amount of significant figures and therefore have no effect on the calculation ■ Counted objects ● Six dogs ( you don’t count half a dog) ■ Defined amounts/constants/conversion factors ● 1000 m per km ■ Formula numbers ● 9.81 m/s^2 ● Adding and subtracting sig figs ○ The result has the same number of DECIMAL places as the least precise measurement in the calculation ■ 19.6 + 58.33 -4.794 = 73.0 ■ The least precise measurement had one decimal place, so the answer has one decimal place ■ 70.2 + 70.4 = 140.6 ■ 20.9 - 15.1 = 5.8 ● Multiplying and dividing sig figs ○ The result has the same amount of sig figs as the least precise measurement ■ 1.5 x 2.0000 = 3.0 ● Combined calculations ○ Do not round until the end ○ Evaluate the significant figures for intermediate calculations before changing from addition/subtraction to multiplication/division and vice versa ● Accuracy vs. Precision ○ Accuracy is how close a value is to the accepted value ■ Think of an arrow hitting the bullseye ○ Precision is a measure of how close several measurements are to each other ■ Think of several arrows consistently hitting the same spot, but not the bullseye ● Dimensional Analysis and Conversion Factors ○ Use unit conversions ○ Remember that units multiply/divide just like the numbers do ○ Values change with units ■ 1 foot is not the same as 1 meter ○ Establish a relationship between two units, then cancel them until you have your desired unit
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