CHEM 121 module 2 study guide Latest Update

CHEM 121 module 2 study guide Latest Update 2025-2026 50 Questions and 100% Verified Correct Answers Guaranteed A+

• steps to solve stoichiometric calculations - CORRECT ANSWER: 1. obtain balanced

reaction

• set up the form around the balanced reaction.
• molecular weights above each formula
• "moles" and "grams" written below each formula
• 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

• 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

• decomposition reactions
• combustion reactions
• double replacement reactions
• single replacement reactions

balancing chemical equations - CORRECT ANSWER: 1. dont change the subscript #'s

• balance oxygen last, hydrogen second to last, and other atoms first
• coefficients can only be placed in front of formulas, and applies to all atoms in the

compound

• when counting, total # of atoms of that element is equal to coefficient*element

subscript*parenthesis subscript 1 / 2

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.

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