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Gen Chem (4)
| Question | Answer |
|---|---|
| What is a mole? | The SI unit for amount of substance; 1 mole = 6.022 × 10²³ particles (Avogadro's number) |
| How is molar mass defined? | The sum of atomic masses of all atoms in one mole of a substance, expressed in g·mol⁻¹ |
| What is percent composition? | % composition = (mass of element / mass of compound) × 100% |
| What is the difference between empirical and molecular formula? | Molecular formula = exact number of atoms; empirical formula = simplest whole-number ratio of atoms |
| How do you find the empirical formula from a molecular formula? | Divide all subscripts by their greatest common factor |
| How do you find the molecular formula from an empirical formula? | Divide molecular molar mass by empirical molar mass; multiply empirical subscripts by that factor |
| How do you find the empirical formula from percent composition? | Assume 100 g sample → convert % to grams → divide by atomic mass → divide all by smallest mole value → multiply to get whole numbers if needed |
| What are the 3 steps for mass-to-mass stoichiometry? | 1. Convert given mass to moles 2. Use molar ratio to find moles of desired substance 3. Convert moles to the required unit |
| How do you identify the limiting reagent? | Convert all reactants to moles; use molar ratios to determine which reactant runs out first |
| Density of water and its significance | ~1 g·mL⁻¹; substances denser than water sink, less dense substances float |
| Formula for percent yield | Percent Yield = (Actual Yield / Theoretical Yield) × 100% |
| Why is percent yield typically less than 100%? | Perfect reactions are unrealistic — product is lost to side reactions, incomplete reactions, or experimental error |
| What is a synthesis reaction? | Two or more substances combine to form one product; usually releases energy (A + B → AB) |
| What is a decomposition reaction? | One compound breaks into two or more products; usually requires energy input (AB → A + B) |
| What is a single displacement reaction? | One element replaces another in a compound (A + BC → AC + B) |
| What is a double displacement reaction? | Two compounds exchange bonding partners (AB + CD → AD + CB); includes neutralization and precipitation |
| What is a combustion reaction? | A substance reacts with O₂ to produce heat and light; complete combustion of hydrocarbons always yields CO₂ and H₂O |
| What is the law of constant composition? | Elements in a compound always combine in a fixed proportion by mass (e.g., H₂O is always 2H : 1O) |
Created by:
smurtab