chapter 5 - chemical quantities & intro to chem reactions

chemical reaction/changes

  • transformation of elements/compounds into diff elements/compounds

  • existing bonds are broken, new ones are formed

5.1 the mole - counting & weighing matter

  • atoms are too small & numerous to count individually

    • avogadro’s number - 6.022 × 10^ 23

  • one mole of anything is the above units of that thing

  • weight of one mole of atoms changes for diff elements

mole & molar mass

  • molar mass

    • mass of 1 mole of the element expressed in grams

    • has same numerical value as its molecular mass, w units g/mol

5.2 writing & balancing equations

  • evidence of a chemical reaction

    • color change

    • emission of light

    • emission/absorption of heat

    • formation of a solid in a previously clear unclouded solution

    • formation of a gas when we add a substance to a solution

  • may occur without any obvious signs, yet chemical analysis may show a reaction has occurred

  • metabolic reactions

    • metabolism - produce compounds & transfer energy needed for living

      • movement

      • speech

      • breathing

      • growth

      • reproduction

writing a chemical equation

  • described by a chemical equation which conveys the identity of the reactants & products & their relative proportions

    • molar ratios of reactants & products are indicated using coefficients, whole numbers that preceded the formulas

  • law of conservation of mass

    • in all chemical reactions, atoms are neither created nor destroyed

  • + - separates 2 or more formulas

  • → - reacts to form products

  • → w triangle - reactants are heated

  • (s) - solid

  • (l) - liquid

  • (g) - gas

  • (aq) ←> aqueous

balancing a chemical equation

  • in a balanced equation

    • no atoms are lost or gained

    • number of atoms on reactant side is = number of atoms of product side for each element

  • combustion of glucose

    • C6H12O6 + 6O2 → 6CO2 + 6H20

stoichiometry calculations

  • balanced chem equation can be used to calculate the

    • max number of moles of product formed from a given number of moles of reactant

    • max mass of product formed from a given mass of reactant

  • mole to mole stoichiometry calculations

    • coefficients provide molar ratio between any 2 substances in the chem reaction

    • mol A → mol B

  • mass to mass stoichiometry calculations

    • mass A → mol A → mole B → mass B 

5.3 types of chemical reactions

  • based on how products differ from reactants

    • combination

      • A+B → AB

      • N2 + O2 → 2NO

    • decomposition

      • AB → A+B

      • 2NaN3(s) → 2 Na(s) + 3N2(s)

    • single replacement

      • A + BC → AC + B

      • Mg(s) + 2HCl(aq) → MgCl(aq) + H2(s)

    • double replacement

      • AB + CD → AD + CB

      • NaOh + HCl → NaCl(aq) + H2O(l)

  • based on important characteristics

    • oxidation-reduction (transfer of electrons) - redox reactions

      • combustion (reaction w elemental oxygen)

      • reactions of organic compounds

    • acid base (transfer of H)

    • precipitation (form a solid)

oxidation-reduction

  • electrons are transferred from one reactant to the other

    • reactant that loses electrons → oxidation

    • reactant that gains electrons → reduction