Chemistry 101 Chapter 2 Notes
Chemistry 101 Chapter 2 Notes CHEM 101
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This 2 page Class Notes was uploaded by Erryn Trottier on Wednesday January 27, 2016. The Class Notes belongs to CHEM 101 at University of Alabama - Tuscaloosa taught by Professor John McDuffie in Spring 2016. Since its upload, it has received 190 views. For similar materials see Generl Chemistry 1 in Chemistry at University of Alabama - Tuscaloosa.
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Date Created: 01/27/16
Chapter 2 Measurement, Problem Solving and The Mole Concept 01/25/2016 Measurement, Problem Solving and the Mole concept Units are quantities used to specify measurements which are critical in chemistry The two most common units are the Metric system (most common) and English system (US) Scientists use the International System of Units (SI), which is based on the metric system Reliability of Measurements Accuracy: refers to how close the measured value is to the actual value Precision: refers to how close a series of measurements are to one another or how reproducible they are Measurements are said to be o Precise if they are consistent with one another; o Accurate only if they are close to the actual value Ex: the first 3 digits are certain and they last digit is estimated : 5.213 Significant Figures o Numbers used to reflect precision o The precision of a measurement depends on instrument used o Exact numbers have an unlimited number of significant figures Density = mass/volume (d)=m/V o An intensive physical property : it does not depend on the amount of substance o The physical properties of mass and volume that determine a substance’s density are extensive: they are dependent on amount o Densities of liquids and gases are affected by temperature Energy o The capacity to do work o Work is defined as the action of a force through a distance ▯ ▯ Energy Kinetic energy- energy of motion Potential energy- energy associated with the position or composition of an object Thermal energy – energy of temperature (a type of kinetic energy) Energy Units- SI unit joule (J) o English unit (cal) o The dietary unit is the calorie (Cal), which is equal to 1000 calories or 1 kilocalorie (kCal) An exothermic process releases energy from the system to the surroundings (-) An endothermic process takes in energy from the surroundings into the system (+) ▯ Calculations and Solving Chemical Problems Unit conversion problems Using units as a guide to solve problems is called dimensional analysis Units should always be included in calculations Dimensional Analysis A unit equation is a statement of two equivalent quantities such as: o 2.54 cm= 1 inch What is a Mole? A mole is a scientist’s “baker dozen” A mole (mol) of anything contains 6.02214 x 10^23 pieces o EX: 1 mol of marbles corresponds to 6.022 x 10^23 marbles 6.022 x 10^23 is Avagadro’s Number The value of the mole is equal to the number of atoms in exactly 12 grams of pure C-12 o 12 g C= 1 mol= 6.022 x 10^23 Mole Conversions 1 mol atom/ 6.022 x 10^23 or 6.022 x 10^23 / 1 mol atom The mass of 1 mol of atoms of an element is the molar mass Ex: 26.98 g Al= 1 mol Al = 6.022 x 10^23 atoms Al o 12.01 g C= 1 mol C = 6.022 x 1-^23 atoms C ▯ ▯ ▯ ▯
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