Ch. 4: Compounds and Stoichiometry Flashcards
what are the two laws of conservation that must be followed when balancing chemical equations?
- law of conservation of mass
- law of conservation of charge
the number of atoms of each element on the reactant side equals the number of atoms of that element on the product side
what do stoichiometric coefficients indicate?
these are the numbers placed in front of each compound
used to indicate the relative number of moles of a given species involved in the reaction
what are the steps to balancing a chemical reaction?
see p. 138
defn: molecule
a combination of two or more atoms held together by covalent bonds
ionic compounds do not form true molecules because of the way in which the oppositely charged ions arrange themselves in the solid state = technically a formula unit with a formula weight
defn + unit: molecular weight
the sum of the atomic weights of all the atoms in a molecule
units are atomic mass units (amu) per molecule
defn + unit: formula weight
of an ionic compound
the sum of the atomic weights of the constituent ions according to its empirical formula
units: amu per molecule
defn: mole
a quantity of any substance equal to the number of particles that are found in 12 grams of carbon-12 (Avogadro’s number)
one mole of a compound has a mass in grams equal to the molecular or formula weight of the compound in amu
defn: Avogadro’s number
6.022 x 10^23 mol^-1
defn + unit: molar mass
the mass of one mole of a compound
unit: g/mol
defn: equivalents
how many moles of the thing we are interested in (protons, hydroxide ions, electrons, or ions) will one mole of a given compound produce?
defn + eqn: gram equivalent weight
the amount of a compound (in grams) that produces one equivalent of the particle of interest
gram equivalent weight = molar mass/n
where n is the number of particles of interest produced or consumed per molecule of the compound in the reaction
eqn: if the amount of a compound is known and we need to determine how many equivalents are present:
equivalents = mass of compound (g)/gram equivalent weight (g)
defn: normality (N)
a measure of concentration given in the units equivalents/L
always assume that a reaction will proceed to completion
eqn: conversion from normality to molarity of a given solute
Molarity = Normality/n
where n is the number of protons, hydroxide ions, electrons, or ions produced or consume by the solute
defn: structural formulas
skeletal representations of compounds that show the various bonds between the constituent atoms of a compound
defn: law of constant composition
any pure sample of a given compound will contain the same elements in an identical mass ratio
defn: empirical formula vs. molecular formula
EMPIRICAL = gives the simplest whole-number ratio of the elements in the compound
MOLECULAR = gives the exact number of atoms of each element in the compound (is a multiple of the empirical formula)
defn + eqn: percent composition
percent composition of an element (by mass) = the percent of a specific compound that is made up of a given element
percent composition = mass of element in formula/molar mass x 100%
can use empirical or molecular formula
defn: combination reaction
has two or more reactants forming one product
A + B –> C
defn: decomposition reaction
the opposite of a combination reaction
a single reactant breaks down into two or more products, usually as a result of heating, high-frequency radiation, or electrolysis
A –> B + C
what does the delta sign over a reaction arrow represent?
the addition of heat
defn: combustion reaction
a special type of reaction that involves fuel (usually a hydrocarbon) and an oxidant (normally oxygen)
in the most common form: these reactants form the two products of carbon dioxide and water
defn: single-displacement reaction
an atom or ion in a compound is replaced by an atom or ion of another element
ex: Cu (s) + AgNO3 (aq) –> Ag (s) + CuNO3 (aq)
defn: double-displacement reactions (metathesis reactions)
elements from two different compounds swap places with each other to form two new compounds
occurs when one of the products is removed from the solution as a precipitate or gas when two of the original combine to form a weak electrolyte that remains undissociated in solution
ex: CaCl2 (aq) + 2 AgNO3 (aq) –> Ca(NO3)2 (aq) + 2 AgCl (s)
defn: neutralization reactions
a specific type of double-displacement reaction in which an acid reacts with a base to produce a salt (and usually water)
ex: HCl (aq) + NaOH (aq) –> NaCl (aq) + H2O (l)
when balancing equations, should you focus on the least represented elements first or the most represented elements first?
LEAST then work your way to the most
defn: limiting reagent/reactant
the reactant that is used up or consumed first in a reaction
it limits the amount of product that can be formed in the reaction
defn: excess reagents (reactants)
the reactants that remain after all the limiting reagent is used up
what are the 2 principles to keep in mind when determining the limiting reagent?
- all comparisons of reactants must be done in units of moles (gram-to-gram comparisons will be useless or misleading)
- it is not the absolute mole quantities of the reactants that determine which reactant is the limiting reagent –> instead the rate at which the reactants are consumed (the stoichiometric ratios of the reactants), combined with the absolute mole quantities determines which reactant is the limiting reagent
defn: theoretical yield vs. actual yield
THEORETICAL = the maximum amount of product that can be generated as predicted from the balanced equation, assuming that all of the limiting reactant is consumed, no side reactions have occurred, and the entire product has been collected
ACTUAL = the amount of product one actually obtains during the reaction
defn + eqn: percent yield
the ratio of the actual yield to the theoretical yield, multiplied by 100
percent yield = actual yield/theoretical yield x 100%
defn: ferrous vs. ferric
cuprous vs. cupric
FERROUS = Fe2+
FERRIC = Fe3+
CUPROUS = Cu+
CUPRIC = Cu2+
how are monatomic anions named?
by dropping the ending of the name of the element and adding -ide
H- = hydride
F- = fluoride
O2- = oxide
S2-= sulfide
N3- = nitride
P3- = phosphide
how are polyatomic anions that contain oxygen (oxyanions) named?
when an element forms two oxyanions, the name of the one with less oxygen ends in -ite, and the one with more oxygen ends in -ate
NO2- = nitrite
NO3- = nitrate
SO32- = sulfite
SO42- = sulfate
mnemonic: oxyanions
the lITEst anions have the fewest oxygens
the heaviest anions ATE the most oxygens
defn: hypo- and per- (ionic compound nomenclature)
hypo- = less oxygen
per- = more oxygen
ClO- = hypochlorite
ClO2- = chlorite
ClO3- = chlorate
ClO4- = perchlorate
how are polyatomic anions that gain one or more H+ ions to form anions of lower charge named?
by adding the word hydrogen or dihydrogen to the front of the anion’s name
HCO3- = hydrogen carbonate OR bicarbonate
HSO4- = hydrogen sulfate OR bisulfate
H2PO4- = dihydrogen phosphate
why are ionic compounds good conductors of electricity in aqueous solutions?
the lattice arrangement is disrupted by the ion-dipole interactions between the ionic components and the water molecules
the cations and anions are now free to move and the solution of ions is able to conduct electricity
defn: electrolytes
solutes that enable solutions to carry currents
the electrical conductivity of aqueous solutions is governed by the presence and concentration of ions in the solution
defn: strong electrolyte vs. weak electrolyte vs. nonelectrolyte
a solute is considered a strong electrolyte if it dissociates completely into its constituent ions
weak electrolyte: ionizes or hydrolyzes incompletely in aqueous solution and only some of the solute is dissolved into its ionic constituents
nonelectrolyte = compounds that do not ionize at all in water, retaining their molecular structure in solution
