Chemistry - Ch 3

Question 1

Stoichiometry

Answer 1

Area of study that examines the quantities of substances consumed and produced in chemical reactions (from the Greek, stocheion “element” & metron “measure”)

Question 2

Chemical equations

Answer 2

way to represent chemical reactions concisely

Question 3

Reactants

Answer 3

starting substances in a chemical reaction

Question 4

Products

Answer 4

substances produced in a chemical reaction

Question 5

Coefficients

Answer 5

Numbers in front of a chemical formula

Question 6

Combination reactions

Answer 6

2 or more substances react to form one product

Question 7

Decomposition reaction

Answer 7

One substance undergoes a reaction to produce 2 or more other substances; common when heated

Question 8

Combustion reactions

Answer 8

rapid reactions that produce a flame

Question 9

Oxidation reactions

Answer 9

reactions that involve intermediate steps (like in the human body)

Question 10

Quantitative significance

Answer 10

numbers in chemical formulas and chemical equations represent precise quantities

Question 11

Formula weight

Answer 11

sum of the atomic weights of each atom in its chemical formula

Question 12

Molecular weight

Answer 12

another name for formula weight if the chemical formula is that of a molecule

Question 13

Formula units

Answer 13

because ionic substances exist as 3D arrays of ions, it’s inappropriate to call molecules; represented by the chemical formula of the substance (Ex. NaCl = 1 formula unit)

Question 14

Percentage composition

Answer 14

percentage by mass contributed by each element in the substance; % element = (# atoms of that element)(atomic weight of each element)/(formula weight of the compound) x 100%

Question 15

Mole (mol)

Answer 15

amount of matter that contains as many objects as the number of atoms in exactly 12g of isotopically pure Carbon12 (6.0221421 x 10^23)

Question 16

Avogadro’s number (N subscript A)

Answer 16

6.0221421 x 10^23 (rounded = 6.02 x 10^23)

Question 17

The mass of a single atom of an element (in amu) is numerically _____ to the mass (in grams) of 1mol of that element

Answer 17

equal

Question 18

Molar mass

Answer 18

the mass in grams of one mole of a substance; the molar mass (in g/mol) of any substance is always numerically equal to its formula weight (in amu)

Question 19

The ratio of the number of moles in each element in a compound gives the _____ in a compound’s empirical formula

Answer 19

subscripts; percent to mass, mass to mole, divide by small (divide by smallest number of moles to find whole numbers), multiply til whole (mass % elements –> (assume 100g sample) grams of each element –> use molar mass to figure moles of each element –> calculate mole ratio (finds empirical formula)

Question 20

Whole number multiple formula

Answer 20

molecular weight/empirical formula weight

Question 21

Empirical

Answer 21

“based on observation and experiment”

Question 22

The coefficients in a balanced chemical equation indicate both the relative number of _____ in the reaction & the relative number of _______.

Answer 22

Molecules (formula units); moles

Question 22

Combustion analysis

Answer 22

experimental technique to determine empirical formulas; commonly used for compounds principally containing carbon and hydrogen as their component elements

Question 23

Limiting reactant/reagent

Answer 23

Reactant that is completely consumed in a reaction; limits the amount of product formed

Question 24

Theoretical yield

Answer 24

Quantity of product that is calculated to form when all of the limiting reactant reacts

Question 25

Actual yield

Answer 25

Amount of product obtained in a reaction

Question 26

Percent yield

Answer 26

Actual yield compared to theoretical; % yield = actual yield/theoretical yield x 100%