Introduction to Chemistry 121 Week 4 Notes
Introduction to Chemistry 121 Week 4 Notes CHEM121A
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This 4 page Class Notes was uploaded by Lindsey Notetaker on Sunday September 25, 2016. The Class Notes belongs to CHEM121A at University of Nevada - Las Vegas taught by Dr. Berg in Fall 2016. Since its upload, it has received 27 views. For similar materials see General Chemistry 1 in Chemistry at University of Nevada - Las Vegas.
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Date Created: 09/25/16
Introduction to Chemistry I-Week 4 Notes (September 19, 2016) Chapter 3: Chemical Reactions and Reaction Stoichiometry Key to my notes: all notes that are taken from the lecture will be the first section, notes I take from the textbook will be the second section, and the vocabulary words from the chapter with definitions will be the last sections! (: Lecture Notes Amu is the atomic mass unit o also called a Dalton o 1 amu is equal to 1.66053 X 10^24 grams Molar mass is in grams Moles are in units o To find the number of atoms, use Avogadro’s number 6.02217 X 10^23 amu Percent composition is 100 X [(how many of element)(atomic mass of element)/(total mass of compound)] o A quick check that you did this correctly is when you add up your answers for all of the elements, you get 100% When finding the empirical formula when you’re only given the percentages, the best thing to do is imagine that the sample size is 100 grams and the percent numbers become the number of grams o Then convert the grams to moles for each element o Divide all the moles by the smallest one o The whole numbers at the end represent the subscripts of the elements If you need to find the molecular formula when you’re only given the molar mass and the empirical formula you do these steps: o First find the empirical mass o Divide the molar mass by the empirical formula o Answer from the division you multiply the subscripts by the answer Reactants (what goes in to a chemical formula) yields products (final result) When balancing equations, the coefficients in front of a compound show how many of that compound there are since the number of atoms in the reactants MUST EQUAL the number of atoms in the products Always make sure that chemical equations are balanced o Place coefficients in front of compounds to ensure that the reactants and products have the number of each element since matter cannot be created nor destroyed o This also helps to gain the mole ratio of compounds Introduction to Chemistry I-Week 4 Notes (September 19, 2016) Mole ratios are the coefficients that allow you in stoichiometry to figure out if you have an amount of one compound, how much of another you can make It also makes comparing easier to figure out what the limiting reactant is Limiting reactant is when ALL of the compound is used in a reaction and other ones have some left, so the one that is consumed entirely is what limits how much of the other compounds are used Textbook Notes In a chemical formula the + is read as “reacts with” and the arrow as “produces” To find the number of atoms in an equation, you multiply the coefficient by the subscripts Coefficients in a reaction tells how many molecules there are o Subscripts tell identity of the compound When balancing an equation, NEVER change subscripts because then you change the compound Sometimes chemical equations tell what state the compound is in o ggas o lliquid o ssolid o aqaqueous solution meaning it is dissolved in water There are three types of patterns with chemical reactions that are seen the most often o Combination reactions This is when two or more substances react to form one product A + B C o Decomposition reactions This is when one substance undergoes a reaction to form two or more substances C A + B o Combustion reaction This is when it is a rapid reaction that produces flames One of the reactants are almost ALWAYS oxygen gas from the air and the other is either a hydrocarbon or a derivatives of hydrocarbons with oxygen When finding the mass of compounds, you use the atomic mass of each element that it is made of and multiple by the amount of each element Since atoms are so small in chemistry we talk about things in moles Introduction to Chemistry I-Week 4 Notes (September 19, 2016) o 1 mole is equal to 6.022 X 10^23 atoms/molecules/ or whatever you are comparing That number is called Avogadro’s number The atomic weight of an element in atomic mass units is numerically equal to the mass in grams of 1 mole of that element When labeling anything , need to be specific so the numbers are not confused with the wrong compound Use mole ratios to find the empirical formula o Make it the lowest whole number ratios To find the molecular formula you divide the molecular weight by the empirical formula weight and then multiple the subscripts by that whole number The limiting reactant is what stops a reaction because there is no longer any more to react with Theoretical yield is the number of products that can be consumed by the limiting reactant\ o The actual yield is almost never the same It is always smaller than the theoretical yield but never bigger This is typically because some reactants might not react the way they are suppose to Percent yield is the comparison of the actual yield of a reaction to the theoretical yield o To find the percent yield you divide the actual yield by the theoretical yield and multiply it by 100 Vocabulary Words Note: These are in order as they showed up in the chapter, not in alphabetical Stoichiometry: the relationships among the quantities of reactants and products involved in chemical reactions Chemical Equation: a representation of a chemical reaction using the chemical formulas of the reactants and products; a balanced chemical equation contains equal number of atoms of each element on both sides of the equation Reactants: a starting substance in a chemical reaction; it appears to the left of the arrow in a chemical equation Products: a substance produced in a chemical reaction; it appears to the right of the arrow in a chemical equation Introduction to Chemistry I-Week 4 Notes (September 19, 2016) Combination Reaction: a chemical reaction in which two or more substances combine to form a single compound Decomposition Reaction: a chemical reaction in which a single compound reacts to give two or more products Combustion Reaction: a chemical reaction that proceeds with evolution of heat and usually also a flame; most combustion involves reaction with oxygen, as the burning of a match Formula Weight: the mass of the collection of atoms by a chemical formula. For example, the formula weight of NO2 (46.0 amu) is the sum of the masses of one nitrogen atom and two oxygen atoms Molecular Weight: the mass of the collection of atoms represented by the chemical formula for a molecule Mole: a collection of Avogadro’s number (6.022 X 10^23) of objects; for example, a mole of H2O is 6.022 X 10^23 H2O molecules Avogadro’s Number: the number of Carbon12 atoms in exactly 12 grams of carbon12; it equals 6.022 X 10^23 inverse mole Molar Mass: the mass of one mole of a substance in grams; it is numerically equal to the formula weight in atomic units Limiting Reactant (limiting reagent): the reactant present in the smallest stoichiometric quantity in a mixture of reactants; the amount of product that can form by the complete consumption of the limiting reactant Theoretical Yield: the quantity f product that is calculated to form when all of the limiting reagent reacts Percent Yield: the rate of the actual (experimental) yield of a product to its theoretical (calculated) yield, multiplied by 100
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