Chapter 3 from Chem 1303

Avogadro’s Number
6.022 x 10^23

1 mole= 6.022 x 10^23 units

chemical formula
A chemical formula shows the ratio by atoms and by moles of elements in the formula
Molar mass of an element
atomic mass in grams of 1 mole or 6.022 x 10^23 atoms of an element
molecular mass
sum of all atomic masses of elements in a formula

“formula weight” and “molecular weight” are often used instead

Mass spectrometer
an instrumental technique used to determine atomic mass or molecular mass
3 types of chemical formulas
1. empirical formula: shows the simplest ratio of the elements present
2. molecular formula: shows the actual number of atoms in one molecule
3. structural formula: shows how the atoms are connected
Percentage Composition
mass % of elements in a compound

theoretical % composition–from given formula

%= (n x molar mass of element)/molar mass of compound x 100%
-where n= number of moles of element (from formula)

chemical reaction
a process in which a substance (or substances) is changed into one or more new substances
chemical equation
uses chemical symbols to show what happens during a chemical reaction
quantitative study of reactants and products


Limiting Reactant Calculations
-one reagent is excess and some is left over
– other quantity “limits” how much product can be made
-analogous to baking brownies when the mix calls for two eggs and you only have one. Thus you use only half the bag of mix
– the limiting reactant is the one that is completely consumed. It determines the maximum amount (yield) of the products
-whenever quantities of both reactants are given, the limiting reactant must be determined!
actual yield
amount of product actually obtained experimentally
theoretical yield
amount of product predicted by balanced equation and limiting reagent
percentage yield
percentage yield = (actual yield/theoretical yield) x 100%

NOTE: the % yield can never be more than 100%

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