Chem 131, Week 2 notes
Chem 131, Week 2 notes CHEM131
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This 3 page Class Notes was uploaded by Christina Notetaker on Friday September 9, 2016. The Class Notes belongs to CHEM131 at University of Maryland - College Park taught by John Ondov in Fall 2016. Since its upload, it has received 14 views. For similar materials see Chemistry I - Fundamentals of General Chemistry in Chemistry at University of Maryland - College Park.
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Date Created: 09/09/16
Chem 131 (9/2/16) Chapter 2: Measurements 2.1 ((Standard units are universal)) Scientific measurements report every digit as true except the estimated last digit, Eg. 3.141592, all numbers are accurate except for the last 2, which is estimated Significant figures depend on measuring device. 2.2 accuracy the measured values’ closeness to the actual value precision a series of measured values’ closeness to each other Measurement errors: random error error of being at either extreme caused by unpredictable changes systematic error consistent inaccuracies usually caused by a measurement device 2.3 weight ≠ density density a physical property measuring degree of consistency; commonly expressed as g/cm or 3 3 g/mc (1 cm = 1 mL) density = mass/volume weight = mass x gravity m 3 d = v (kg/m )* *SI derived unit Physical properties: intensive property independent of amount or size; used to identify types of substances eg. density, temperature, hardness extensive property depends on amount of substance eg. mass, volume, length 2.4 Fundamental Components of Universe: Mass and Energy energy capacity to do work work force exerted over a distance: Force F W = displacement = Δd (J) work = change in kinetic energy, aka workenergy theorem: W = KE −KE f i J) Types of energy: kinetic energy energy possessed while in motion, symbol KE: 1 2 KE = mv 2 (J) potential energy stored energy relative to an object’s position, symbol U (J); commonly expressed as kJ (1kJ=1000J) thermal energy energy associated with temperature; type of kinetic energy; generated by individual atoms’ or molecules’ motion heat process of transferring thermal energy between substances Energy Transformations Law of conservation of energy energy is neither created nor destroyed; total quantity of energy remains constant ***systems with high potential energy tend to be unstable until released to return to equilibrium U → KE or U → KE +E thermal Units of Energy calorie amount of energy required to increase temperature of 1g water by 1℃, symbol cal 6 1cal = 4.184J = 1.16 x 10 kWh Chemical processes: exothermic system loses energy to surroundings, (Δ) endothermic system gains energy from surroundings, (+Δ) 2.5 Unit Conversion dimensional analysis using units as a guide to solving problems conversion factor fractional quantity Given unit × desired unit = desired unit given unit 2.6 ProblemSolving Maneuvers 1) Identify the givens data and variables provided 2) Identify endpoint what to solve for 3) Use a conceptual plan or a visual outline Eg. 5g CO 2e produced from belching cows. How many CO atoms do co2 belch? Givens: 5g Carbon Unknown: ? CO ato2 (5g CO 2(12g/mol C + 2(18g/mol) O ) = 21041 mol CO 2 (0.1 mol CO ) x (6.022 x 10 ) = 6.3 x 10^22 CO atoms 2 2 2.7 mole abbrev. mol, amount of material consisting 6.022 x 10 particles: 23 (1 mol of atoms = 6.022 x 10 atoms) 23 Avogadro’s number 6.022 x 10 particles (memorize***) 1 mole = number of atoms in exactly 12 g pure Carbon12: [12g C = 1mol C atoms = 6.022 x 10 C atoms] 3 molar mass mass of 1mol of atoms of an element or chemical substance