stoichiometry - used to find quantitative information about the substances in reactions
- based on law of conservation of mass (discovered by Antoine Lavoisier)
- atoms are neither created/destroyed in chemical reactions
- atoms are only rearranged
chemical equations - represents chemical reactions
- reactants >> products
- reaction must have same number of each atom on both sides to be balanced
- balanced equation - Cl2 + O >> Cl2O
- unbalanced equation - H2 + O2 >> H2O
- use only coefficients to balance the equation (don't change subscripts)
- best to always balance the elements that appear in the fewest formulas on each side
combination reaction - 2+ substances react to form 1 product
- metal/nonmetal combine to form ionic solids
- A + B >> C
- C + O2 >> CO2
- CaO + H2O >> Ca(OH)2
decomposition reaction - 1 substance reacts to produce 2+ substances
- usually involves heating
- C >> A + B
- CaCO3 >> CaO + CO2
- 2KClO3 >> 2KCl + 3O2
combustion reaction - rapid reactions that produce a flame
- usually involves O
- usually forms water and carbon dioxide when hydrocarbons are burned
- C3H8 + 5O2 >> 3CO2 + 4H2O
- 2CH3OH + 3O2 >> 2CO2 + 4H2O
formula weight - sum of the atomic weights in each chemical formula
- equal to atomic weight if finding the weight of an element
- aka molecular weight if finding the weight of a compound
- formula units - represents the chemical formulas of substances; useful to describe ionic compounds (formula unit of ionic compounds same as its empirical formula)
- percent composition - percentage of mass of each element in a substance; equal to number of atoms times atomic weight divided by formula weight
- Find the percent composition of carbon in C2H2 (acetylene)
- 2(12) / (2 x 12 + 2 x 1) = 24 / 26 = 0.92 = 92%
- Find the percent composition of oxygen in C6H8O6 (ascorbic acid)
- 6(16) / (6 x 12 + 8 x 1 + 6 x 16) = 96 / 176 = 0.55 = 55%
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