chapter 3: equations, the mole, and chemical formulas Flashcards Preview

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Flashcards in chapter 3: equations, the mole, and chemical formulas Deck (97):
1

stochiometry: the study of .... relationships involving the

quantitative; substances in chemical reactions

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knowledge of ... is central to chemistry

how different substances react

3

equations compactly describe

chemical changes

4

Reactants are the substances that are

consumed

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product is the substance/substances that are

formed

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chemical equation describes the .. and ... of ... and ... in a chemical reaction

identities; relative amounts; reactants; products

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balanced equation is consistent with the

law of conservation of mass

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coefficient represents the number of ...

units of each substance involved in the equation

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use the lowest possible

coefficients when balancing

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do not alter the subscripts in any of the substances when

balancing equations

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fractional coefficients are generally avoided because a

fraction of a molecule cannot exist

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(symbols) s

solid

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(symbols) l

liquid

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(symbols) g

gas

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(symbols) aq

substances dissolved in water (aqueous solution)

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polyatomic ions behave as a ... on both sides of the reaction, and are balanced as a ...

single unit; single unit

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three types of reactions:

neutralization, combustion of organic compounds, oxidation-reduction

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the fourth common type of reaction is

precipitation

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(acids and bases) simplest definition of an acid: any substance that dissolves in water and

yields the hydrogen cation

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(acids and bases) acids are generally ...., but when they dissolve in water they ...

molecular compounds; ionize

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(acids and bases) ionization: when molecular compounds

separate into ions in solution

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(acids and bases) the hydrogen cation can also be written as

H3O+ (hydronium ion)

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(acids and bases) writing the hydronium ion indicates that the hydrogen cation is associted with a ..., and that bare H+ ions are not ....

water molecule; present in solution

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(acids and bases) in reaction stoichiometry, the ... representation is preferred becaue it ...

H+; simplifies equations

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(acids and bases) the simplest definition of a base: any substance that produces

hydroxide anion in water

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(acids and bases) the most common bases are the hydroxides of elements in groups

1 and 2

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(acids and bases) the eequtions for acids and bases dissolving in water show

charged species

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(acids and bases) when you write an equation that contains charged species, the sume of the charges on each side of the equation

must be the same, along with the number of atoms

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(acid-base reactions: neutralization) neutralization: the reaction of an acid with a base yields

water and the respective salt

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(acid-base reactions: neutralization) a salt is an ionic compound composed of a

cation from a base and an anion from an acid

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(acid-base reactions: neutralization) the number of hydrogen ions contributed by the acid and the number of hydroxide ions contributed by the base are equal to ... and to the ...

each other; number of water molecules formed

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(combustion reactions) combustion reaction is the process of ..., typically involves reaction with ...

burning; oxygen

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(combustion reactions) assume that the products of the combustion of organic compounds that contain only carbon, hydrogen, and oxygen are always

CO2 and H2O

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(combustion reactions) depending on how the reaction is carried ou, the water molecules could be in either the

gas of the liquid state

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(oxidation-reduction reactions) combustion reactions are a special class of chemical reactions known as

oxidation-reduction reactions

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(oxidation-reduction reactions) oxidation refers to the ... of electrons by a substance

loss

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(oxidation-reduction reactions) reduction refers to the ... of electrons by a substance

gain

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(oxidation-reduction reactions) oxidation-reduction reaction is one in which electrons are

transferred from one species to another

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(oxidation-reduction reactions) in all oxidation-reduction reations, some atoms are .. and some are ..

oxidized; reduced

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(oxidation-reduction reactions) we often need to identify which compounds are oxidized and which are reduced to understand the ... of the reaction, and to help ... complicated reactions

chemistry; balance

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(oxidation-reduction reactions) oxidation numbers are a bookkeeping method. They are ... numbers assigned to ... based on a set of rules

integer; atoms in molecules or ions

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(oxidation-reduction reactions) an atom in its elemental state has an oxidation number of

zero

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(oxidation-reduction reactions) monatomic ionis in ionic compounds have an oxidation number equal to the

charge of the ion

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(oxidation-reduction reactions) fluorine always has the ox number

-1

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(oxidation-reduction reactions) oxygen is generally

-2

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(oxidation-reduction reactions) hydrogen combined with a nonmetal is generally... and ... when combined with metals

+1; -1

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(oxidation-reduction reactions) halogens are generally

-1

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(oxidation-reduction reactions) all other atoms are assigned oxidation numbers so that the sum of the oxidation numbers for all of the atoms in a species is equal to the

charge of the species

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(oxidation-reduction reactions) to determine which species are oxidized/reduced, wee always start with

assigning oxidation numbers

50

one mole is equal to the number of atoms in exactly

12 grams of the carbon-12

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the mole is the ... of the quantity "amount of a substance"

unit

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the number of atoms in 12 g of carbon-12 was experimentally measured and found to be

6.022 x 10^23 atoms

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6.022 x 10^23 is known as

avogadro's number

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thus, 1 mol of anything has ... of those things

6.022 x 10^23

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balanced chemical euations are balanced in terms of ..., as well as molecules

moles

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the molar mass (M) of any atom, molecule, or compound is the mass in grams of

one mole of that substance

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thr molar mass of an element is numerically equal to the

atoic mass and molecular mass and formula mass

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the molar mass of a substance is used to convert between ...

mass (in grams) and amount (in moles)

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when a new compound is discovered, one of the first tests done may be to determine its

percent composition

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the mass percentage of each element ina compound is calculated from the

chemical formula and the atomic masses of each eelemtn

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the percentage composition of a compound can be based on its .... as well as on its ...

empiricial formula; molecular formula

62

by reversing the mass percentage calculation, chemists can calculate the ... of a newly prepared compound

empirical formula

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combustion analysis: determines the quantity of ... and ... in a sample of an

carbon; hydrogen; organic compound

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This process involves burning a sample in excess ...oxygen and determining the amount of ...and ...generated

oxygen; CO2; H2O

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The percentage of carbon and hydrogen in the sample can be calculated from the

measured masses of CO2 and H2O

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in combustioin nalysis, the msses of each of the elements present, is not determined

directly

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the first step in determining a molecular formula is to experimentally determine the

empirical formula

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the empirical formula can be determined from either the ... or ... of the elements in a sample

masses; mass percentages

69

this calculation yields only the empirical formula, because the composition by mass is based only on the relative number of ... of each element in the compound

atoms

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the empirical formula is usually al you need to describe the composition of a

ionnic comound

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dditional experimental information is needed tod etermine the correct formula of a

molecular compound

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to calculate the relative number of moles, we need to convr tthe mass of each element into the

moles of atoms of that eleemnt

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procss for determining the empirical formula: composition to moles of each element by using .... to the empricial formula by ...

the moar mass of elements; dividng by the smallest number

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empirical formulas are often determined from the results of experiments that provid

mass percentage composition

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if the composition is given as percentages, assum ethat a ... sample has been analyzed

100.0 g

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to calculate the molecular formula from the empirical formula, we must know the ... of the compound from experiment

molar mass

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the molecular formula must be a whole-number multiple of the ..., where n is the number of times the empirical formula occurs in the ..

empirical formula; molecular formula

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n is calculated as follows: n =

molar mass of compound/ molar mass of empirical formula

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chemical equations express ...

stoichiometry

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the coefficients of the balanced chemical equation relate amounts of each substance in the equation to any

other substance in the equation

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chemical equations quantitaively expres stochiometric relationships in both numbers of ... and in ...

molecules; moles

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(proedure for using an equation to calculate mass of product/reactnt in chemical reaction) write the balanced

hemical equation

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(proedure for using an equation to calculate mass of product/reactnt in chemical reaction) start with the given mass of one substance annd calculate ... of this substanc

the number of moles

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(proedure for using an equation to calculate mass of product/reactnt in chemical reaction) use the coefficients of the balaned equation to calculate the moles of the ... from the moles of the ...

desired substance; given substance

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(proedure for using an equation to calculate mass of product/reactnt in chemical reaction)calculate the mass of the ...

desired substance

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theoretical yield is the maximum quantity of product that can be obtained from a ..., based on the amounts of ...

chemical reaction; starting materials

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limiting reactant: the reactant that is completely ... when the chemical reaction occurs

consumed

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when we calculate the amount of product formed, the calculation must be based on the ..., not the reactants that are present in excess

limiting reactant

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the limiting reactant is the one that yields the .. of any one product

smallest amount

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sometimes ... occur and consume some starting material without forming the expeced product

side reactions

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actual yield: mass of product ... from a reaction, always .. than the theoretical yield

isolated; less

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percent yield =

actual yield/ theoretical yield x 100%

93

laboratory workers occasionally observe an actual yield that is greater than the theoretical yeield because the desired substance may be ... by other products or by ..

contaminated; excess reactants

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any time the actual yield exceeds the theoretical yield, further investigation must be done to

determine the source of error

95

sometimes the result of a chemical reactiondepends on an

excess of one or more reactants

96

an excess of one or more reactants can usually aoid

undesirable side products

97

in other cases, an excss of certain reactants may be needed to... or to ... it takes for the reaction to occur

increase the yield; shorten the length of time