Chem Exam Chapter 9

Stoichiometry

Stoichiometry

the study of the quantitative relationship between chemical formulas and chemical equations

element; measure

stoichiometry origins: stoicheion meaning , metron meaning_

composition stoichiometry

the mass relationship of elements in compounds

reaction stoichiometry

the mass relationship between reactants and products in a chemical reaction/change

mole

a counting unit in science which is equivalent to 6.022*10^23 molecules, particles, formula units, or atoms of a substance

given/known

information within an analytical problem with both known number values/quantities and known units

unknown/find

information within an analytical problem that is expected to be determined with unknown numbers/values but known units

Products

symbol (P); new substances formed from change; found after the arrow symbol; formed when new bonds are formed

reactants

symbol (R); original substances that undergo change; found before the change arrow; have bonds broken

law of conservation of mass

matter can neither be created nor destroyed, but is conserved

coefficients

small whole numbers placed in front of each substance in a chemical equation to balance the products and reactants

mole ratio

a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction

Antoine Laurent Lavoisier

considered the father of modern chemistry; helped establish chemistry as a science; emphasized the importance of quantitative analysis

composition stoichiometry equation

Moles(compound) → moles(elements)

reaction stoichiometry equation

? mole x → ? mole y

molar mass

symbol :Mx; the total mass of a mole of substance

molar mass equation

? g x = 1 mole x

Given

G in GUESS method

Unknown

U in GUESS method

Equation

E in GUESS method

Setup

1st S in GUESS method

Solution

2nd S in GUESS method

Ideal stoichiometric condition

assumption within stoichiometry where all reactants are completely converted into products

Limiting reagent

symbol: L.R.; reactant substance that is completely consumed in a chemical reaction

limiting reagent importance

determines or limits the amount of products formed

excess reagent

symbol: E.R. or EXR; reactant substance that remains after completion of chemical reaction or reactant substance that is partially consumed

consumed excess reactant

reactant amount used or rearranged or consumed by the chemical reaction

original excess reactant

reactant amount at the beginning before any chemical reaction has occured

theoretical yield

symbol TY; the maximum amount of a product that can be possibly produced from a given amount of reactant when all of this reactant is consumed

actual yield

symbol AY; the measured amount of a product obtained from a reaction that is collected in the lab

AY importance

can never be greater than the TY

percent yield

symbol PY; the ratio of actual yield to theoretical yield multiplied by 100

PY=AY/TY*100

PY equation

AY=(PY)(TY)/100

AY equation

TY=AY/PY*100

TY euation

80-95%

ideal PY

PY importance

the higher the PY, the more effective the chemical reaction

over 100% PY

___ means possible contamination; possible impurity from unused [unreacted] reactant(will be on test); means the AY is larger than the TY, which is impossible unless something went wrong

better technique; better equipment; larger reaction/sample size

How can the PY of a chemical reaction be improved?

Standard stoichiometry

one given, one unknown, no mention of L.R. or E.R.; use the DiAn to determine how many steps within mole map

Stoichiometry with pre-identified L.R.

given L.R., TY is unknown; convert the units of limiting reagent into the units of the specified product, the result is the TY

stoichiometry with unidentified L.R.

multiple givens; label all the reactants and products, convert all given reactants into units of a chosen product(multiple setups), compare the product when all units are the same

the lowest product is the TY, the higher product is false

how to identify the TY with two values

percent yield stoichiometry

asks for PY, AY, or TY

remaining excess reagent stoichiometry

unknown is how much excess; identify the L.R. and E.R. reactants, use Di An and convert L.R. units into excess reagent units, subtract consumed

Original-consumed=remaining

remaining excess reagent equation