Essential Ideas CHEM 1127Q 001
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This 4 page Class Notes was uploaded by Caitrín Hall on Tuesday January 26, 2016. The Class Notes belongs to CHEM 1127Q 001 at University of Connecticut taught by Fatma Selampinar (TC), Joseph Depasquale (PI) in Spring 2016. Since its upload, it has received 312 views. For similar materials see General Chemistry in Chemistry at University of Connecticut.
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Date Created: 01/26/16
Chapter 1: Essential Ideas 1.1 Chemistry in Context Chemistry – the study of the composition, interactions, and properties of matter “Central science” Based on observation and experimentation The scientific method – path of discovery that answers a question with experimental verification and modification 1. Question and observation 2. Hypothesis – tentative explanation of observations that guides experiment 3. Experimental verification 4. Theory – satisfactory, testable explanation of natural observation; can be modified! 1.2 Phases and Classification of Matter Phases of matter – occupies space and has mass Solid – rigid object with fixed shape and volume Liquid – variable shape that flows to fill container; fixed volume Gas – indefinite shape and volume expand and contract to fill container Plasma – gaseous state of matter with charged particles; high temp environment Law of conservation of matter – no matter is created nor destroyed during chemical reactions or phase changes Atoms & molecules: Atom – smallest particle of an element that retains its properties and can enter into chemical combinations; basic “building blocks” Molecule – two or more atoms joined by chemical bond; atoms can be identical or different Classifying matter: Pure substance – constant composition; can be either compounds or elements o Elements – cannot be broken down by chemical changes; see periodic table o Compounds – can be broken down by chemical changes; consist of two or more atoms of different elements Mixtures – composed of two or more types of matter present in varying amounts; can be separated by physical change o Heterogeneous – composition varies from point to point o Homogeneous (solution) – visibly but not chemically uniform throughout 1.3 Physical and Chemical Properties Properties make substances distinguishable Physical property – characteristic of matter not associated with change in chemical composition; ex) density, color, hardness, melting/boiling pts., conductivity o Physical change – change in state/properties of matter without accompanying change in chemical composition (identity of substances in the matter) Chemical property – change (or inability to change) from one type of matter into another; ex) flammability, toxicity, acidity, reactivity, heat of combustion o Chemical change – produces at least 1 type of matter different than original Extensive property – depends on & is directly proportional to amount of matter; ex) mass, volume, heat Intensive property – does not depend on amount of matter; ex) temperature 1.4 Measurements Provide macroscopic info included in hypotheses, theories, and laws that describe the behavior of matter and energy in macroscopic and microscopic chemistry 1. Magnitude (decimal or scientifically notated #) 2. Unit – standard of comparison SI Units 3. Indication of uncertainty SI base units: Length = meter (m) Mass = kilogram (kg) o Chem uses gram (g) or milligram (mg) o Measures amount of matter in object Temperature = kelvin (K) is most convenient; Celsius (degrees C) is allowed o 0 degrees Celsius = 273.15 kelvins o Temp in F = 1.8(temp in C) + 32 degrees Time = second (s) Derived SI units: Volume – measures amount of space occupied by object o Cubic meter (m^3) o Cubic decimeter = liter (L) o Cubic centimeter (cm^3) = milliliter (mL) Density – ratio of mass of substance to its volume o Intensive property o d = m/v o SI unit = kg/m^3 o In chem we use g/cm^3, g/mL, g/L 1.5 Measurement Uncertainty, Accuracy, and Precision Exact numbers and defined quantities can be counted and do not change during the counting process; free from uncertainty Numbers of measured quantities are not exact because they have uncertainty Significant figures – all digits in a measurement including the last uncertain digit o All nonzero numbers are significant o Captive zeros—between nonzero numbers—are significant o Leading zeros – NOT significant o Trailing zeros – NOT significant unless # is a decimal or in scientific notation Significant figures in calculations o Multiplication/division – result contains same # significant figures as does the factor with the least # significant figures o Addition/subtraction – result contains same # decimal places as the factor with the least # decimal places Accuracy – results are vey close to true or accepted value Precision – results are very similar to each other Round up only if the first insignificant figure is greater than or equal to 5, otherwise, don’t change the last significant figure 1.6 Mathematical Treatment of Measurement Results Dimensional analysis uses conversion factors—ratios of 2 equivalent quantities with different units—to cancel unnecessary units Tips: Begin with the initial unit Multiply by the conversion factor The desired unit should be the numerator of the conversion factor The unit of the initial quantity should be the denominator so it “cancels” *because any unit divided by itself equals 1*
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