Chapter 3

Question 1

Define chemical Stoichiometry

Answer 1

Area of study where the quantities if materials consumed and produced in chemical reactions are considered

Question 2

If you know the __ __ of objects, the objects behave as they were all __

Answer 2

Average mass; Identical

Question 3

To count atoms, determine the # of __ in a sample by finding its __

Answer 3

Atoms; Mass

Question 4

Modern system of atomic masses is based in __ as the standard

Answer 4

12C

Question 5

__ is assigned a mass of exactly __ atomic mass units (amu)

Answer 5

12C; 12

Question 6

Define mass spectrometer

Answer 6

An instrument used to determine the relative masses of atoms or the isotopic composition of a natural element by the deflection of their ions on a magnetic field

Question 7

Accelerating ions produce own __ __, interacts with applied __ __, which tends to change the path of the __ (most massive __ are deflected the __ & separate)

Answer 7

Magnetic field; Magnetic field; Ion; Ions; Least

Question 8

Masses of atoms are called __ __; atomic mass of _ is an average value of isotopes

Answer 8

Atomic weight; C

Question 9

Define mole

Answer 9

Number equal to the number of carbon atoms in exactly 12 grams of pure 12C

Question 10

Define average atomic mass

Answer 10

Average mass of an element

Question 11

Define molar mass (molecular weight)

Answer 11

Mass in grams of one mole of the compound

Question 12

Define Avogadro’a number

Answer 12

6.022 • 10^23; number of units of a substance in one mole of it

Question 13

Mass of 1 mole of an element is equal to its __ __ in __; 6.022 • 10^23 __ = 1 _

Answer 13

Atomic mass; Grams; Amu; g

Question 14

To find the molar mass, sum the masses of the __ __

Answer 14

Component atoms

Question 15

2 common ways to describe the composition of atoms

Answer 15

of atomsPercentage of elements

Question 16

Define mass percent (weight percent)

Answer 16

Percent by mass of a given element in a compound ((mass of element in 1 mole of compound / total mass of 1 mole of compound) x 100)

Question 17

To determine the formula of a compound, most often a __ sample of the compound is either __ into its component elements or __ with oxygen to produce substances that are than __ and __

Answer 17

Weighed; Decomposed; Reacted; Collected; Weighed

Question 18

Since the formula of a compound indicates the number of __ in the compound, masses of the elements must be converted to number of __ (easiest way is to use __ g)

Answer 18

Atoms; Atoms; 100.00

Question 19

Numbers very close to whole numbers should be rounded to __ numbers for the integers

Answer 19

Whole

Question 20

Define empirical formula

Answer 20

Simplest whole number ratio of atoms in a compound

Question 21

Define molecular formula

Answer 21

Exact formula of a molecule, giving types of atoms and the number of each type

Question 22

Molecular formula determination method 1 (4)

Answer 22

1) Obtain empirical formula2) compute the mass corresponding to the empirical formula 3) calculate the ratio (molar mass / empirical formula mass) 4) multiply the empirical formula by this integer to get the molecular formula

Question 23

Empirical formula determination (4)

Answer 23

1) base calculations in 100g, each percent will then represent the mass in grams of that element2) determine number of moles of each element present in 100g of compound using atomic masses 3) divide each value of number of moles by the smallest values 4) multiply each number by an integer so the results are whole numbers

Question 24

Define chemical equation

Answer 24

A representation of a chemical reaction showing the relative numbers of reactant and product molecules, and the nature of the reactants

Question 25

Molecular formula determination method 2 (3)

Answer 25

1) Using mass %s and the molar mass, determine the mass of each element present in one mole of compound 2) determine the # of moles of each element present in one mole of compound 3) integers represent subscripts in the molecular formula

Question 26

Define reactants

Answer 26

Starting substance in a chemical reaction; on left side of chemical equation

Question 27

Chemical equations give the __ __ of the reactants and products

Answer 27

Physical states

Question 28

Define products

Answer 28

Substance resulting from a chemical reaction; on right side of chemical equation

Question 29

Define balancing a chemical equation

Answer 29

Making sure atoms are neither created not destroyed and all atoms present in the reactants must be accounted for among the products

Question 30

Numbers if reactants & products are indicated by the __

Answer 30

Coefficients

Question 31

Writing and balancing equations (3)

Answer 31

1) Determine reaction occurring (reactants, products, physical states) 2) write the unbalanced equation 3) balance the equation by starting with the most complicated molecules, determine coefficients necessary so the same number of each type of atom appears in both reactant and product sides, do not change formula of any compound

Question 32

Define mole ratio

Answer 32

Ratio of moles of a substance to moles of another substance in balanced equations

Question 33

Define haber process

Answer 33

The manufacture of ammonia from nitrogen & hydrogen, carried out at high pressure & high temperature with the aid of a catalyst

Question 34

Calculating masses of reactants and products in chemical reactions (5)

Answer 34

1) balance equation2) convert known mass of reactant or product to moles of that substance 3) use balanced equation to set up mole ratios4) use mole ratios to calculate number of moles of desired reactant or product 5) convert from moles back to grams if necessary

Question 35

Define Stoichiometric quantities

Answer 35

Quantities of reactants mixed in exactly the correct amounts so that all are used up at the same time

Question 36

Always determine which reactant is __ to correctly calculate amounts of product form

Answer 36

Limiting

Question 37

Define limiting reactant (limiting reagent)

Answer 37

Reactant that is completely consumed when a reaction is run to completion, and limits the amount of products that can be formed

Question 38

Define theoretical yield

Answer 38

The maximum amount of a given product that can be formed when the limiting reactant is completely consumed

Question 39

Define percent yield

Answer 39

Actual yield of a product as a percentage of the theoretical yield

Question 40

Solving a Stoichiometry problem involving masses of reactants & products (5)

Answer 40

1) write & balance the equation for the reaction2) convert the known masses of substances to moles3) determine which reactant is limiting4) using the amount of the limiting reactant and the appropriate mole ratios, compute the number of moles of the desired product 5) convert from moles to grams, using the molar mass

Question 41

Percent yield = (__ yield in g / __ yield in g) x 100%

Answer 41

Actual; Theoretical

Question 42

Percent yield can indicate the __ of a particular __ or __ reaction

Answer 42

Efficiency; Laboratory; Industrial