CHEM 121 module 2 study guide Latest Update
2025-2026 50 Questions and 100% Verified
Correct Answers Guaranteed A+
4 steps to solve stoichiometric calculations - CORRECT ANSWER: 1. obtain balanced
reaction
2. set up the form around the balanced reaction.
a. molecular weights above each formula
b. "moles" and "grams" written below each formula
3. put the given info from the problem in its correct place (under the substance it
belongs with - this is what we call the known substance since we have info given about
it
4. do the calculations using the following equations
---moles=grams/MW
---grams=moles*MW
---moles (unk)=(coeff unk/coeff kno)*moles kno
5 types of reactions - CORRECT ANSWER: 1. combination reactions
2. decomposition reactions
3. combustion reactions
4. double replacement reactions
5. single replacement reactions
balancing chemical equations - CORRECT ANSWER: 1. dont change the subscript #'s
2. balance oxygen last, hydrogen second to last, and other atoms first
3. coefficients can only be placed in front of formulas, and applies to all atoms in the
compound
4. when counting, total # of atoms of that element is equal to coefficient*element
subscript*parenthesis subscript
, combination (synthesis) reactions - CORRECT ANSWER: reaction in which single
product is formed from multiple reactants
combustion reaction - CORRECT ANSWER: reaction in which a hydrocarbon
(compound containing only C,H or C,H,O) is reacted with elemental oxygen (O2) to form
CO2 and H2O
concentrated vs dilute - CORRECT ANSWER: Concentrated: strong: lots of solute
Dilute: weak: less solute
Both: qualitative (subjective) measurements
concentration - CORRECT ANSWER: amount of solute present in solvent
concentration terms - CORRECT ANSWER: mass percent, molarity, molality
decomposition reaction - CORRECT ANSWER: reaction in which a single reactant is
converted to multiple products
double replacement reaction - CORRECT ANSWER: reaction in which 2 ionic
compounds exchange their ions to form a non-ionic (molecular) compound product
either as (1. a solid, insoluble precipitate) (2. a gas) (3. a molecular compound) the
formation of which drives the reaction to completion
electrolyte solutions - CORRECT ANSWER: solutions of electrolytes conduct electric
current.
empirical formula (how to find it %) - CORRECT ANSWER: 1. divide each element % by
the atomic weight of the elem.
2025-2026 50 Questions and 100% Verified
Correct Answers Guaranteed A+
4 steps to solve stoichiometric calculations - CORRECT ANSWER: 1. obtain balanced
reaction
2. set up the form around the balanced reaction.
a. molecular weights above each formula
b. "moles" and "grams" written below each formula
3. put the given info from the problem in its correct place (under the substance it
belongs with - this is what we call the known substance since we have info given about
it
4. do the calculations using the following equations
---moles=grams/MW
---grams=moles*MW
---moles (unk)=(coeff unk/coeff kno)*moles kno
5 types of reactions - CORRECT ANSWER: 1. combination reactions
2. decomposition reactions
3. combustion reactions
4. double replacement reactions
5. single replacement reactions
balancing chemical equations - CORRECT ANSWER: 1. dont change the subscript #'s
2. balance oxygen last, hydrogen second to last, and other atoms first
3. coefficients can only be placed in front of formulas, and applies to all atoms in the
compound
4. when counting, total # of atoms of that element is equal to coefficient*element
subscript*parenthesis subscript
, combination (synthesis) reactions - CORRECT ANSWER: reaction in which single
product is formed from multiple reactants
combustion reaction - CORRECT ANSWER: reaction in which a hydrocarbon
(compound containing only C,H or C,H,O) is reacted with elemental oxygen (O2) to form
CO2 and H2O
concentrated vs dilute - CORRECT ANSWER: Concentrated: strong: lots of solute
Dilute: weak: less solute
Both: qualitative (subjective) measurements
concentration - CORRECT ANSWER: amount of solute present in solvent
concentration terms - CORRECT ANSWER: mass percent, molarity, molality
decomposition reaction - CORRECT ANSWER: reaction in which a single reactant is
converted to multiple products
double replacement reaction - CORRECT ANSWER: reaction in which 2 ionic
compounds exchange their ions to form a non-ionic (molecular) compound product
either as (1. a solid, insoluble precipitate) (2. a gas) (3. a molecular compound) the
formation of which drives the reaction to completion
electrolyte solutions - CORRECT ANSWER: solutions of electrolytes conduct electric
current.
empirical formula (how to find it %) - CORRECT ANSWER: 1. divide each element % by
the atomic weight of the elem.
