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4. Chemical reactions

physical change: substance undergoes a change in properties but not a change in composition
examples
changes in the phase of a substance (solid, liquid, gas)
formation/separation of mixtures and substances
chemical change: substances are transformed into new substances, typically with different compositions
possible evidence
production of heat or light
formation of a gas
formation of a precipitate
color change
chemical equations
balanced: contains equal numbers of atoms of every element before and after the change occurred (mass and charge are conserved)
balanced molecular equation: represents the overall reaction stoichiometry (not necessarily the actual forms in solution)
complete ionic equation: represents as ions all products and reactants that are strong electrolytes
net ionic equation: represents only the components undergoing change
can be translated into symbolic particulate representations
classifying changes
chemical changes: involve the breaking and/or formation of chemical bonds
physical changes: only changes in intermolecular interactions (e.g. phase changes)
physical process sometimes involve breaking of chemical bonds (e.g. dissolving salt in water can be defined as either physical or chemical)
stoichiometry
it is possible to calculate product amounts by using known reactant amounts, or vice versa
coefficients: proportions of substances involved in the reaction
can be used in calculations involving moles
can be combined with ideal gas law and molarity calculations to quantitatively study gases and solutions
titrations: used to determine the amount of an analyte in solution
titrant: has a known concentration of a species that reacts specifically and quantitatively with the analyte
equivalence point: when the analyte is totally consumed by the reacting species in the titrant
often indicated (endpoint) by a change in property (e.g. color)
types of chemical reactions
acid-base reaction: transfer of one or more protons (H⁺ ions) between chemical species
oxidation-reduction/redox reaction: transfer of one or more electrons between chemical species
indicated by changes in oxidation numbers of the involved species
combustion: hydrocarbon reacts with oxygen gas to produce carbon dioxide and water
elements are transferred from the species that is oxidized to the species that is reduced
oxidation numbers
atom: 0
monatomic ion: charge
fluorine: -1
oxygen: -2
hydrogen: +1
precipitation reaction: mixing ions in aqueous solution to produce an insoluble or sparingly soluble ionic compound
salts soluble in water: sodium (Na⁺), potassium (K⁺), ammonium (NH₄⁺), nitrate (NO₃⁻)
acid-base reactions
Brønsted-Lowry acid: proton donor
Brønsted-Lowry base: proton acceptor
aqueous solutions: water can both accept and donate protons
when an acid or base ionizes in water, the conjugate acid-base pairs can be identified and their relative strengths compared
oxidation-reduction (redox) reactions: can be balanced from half-reactions
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