notes4 - Unit 4 Chemical Reactions Physical change: a...

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Unit 4 – Chemical Reactions Physical change: a change is a substance that does not change the identity (composition) of the substance; a change in size, shape, mass, volume, phase, etc. Phase changes: Melting: solid liquid absorbs energy, +E Freezing: liquid solid releases energy, -E Vaporization: liquid gas absorbs energy, +E (boiling) Condensation: gas liquid releases energy, -E Sublimation: solid gas absorbs energy, +E (dry ice) Deposition: gas solid releases energy, -E (frost) Chemical change: a change in which a substance undergoes a change in identity (composition); burning, rusting, decomposing, etc Indicators of a chemical change Heat, light or sound are produced A change in odor or color A precipitate forms when two solutions are mixed Chemical reaction: a process in which new substances are created Chemical equation: a symbolic representation of chemical reactions Symbol or term Explanation Reactants Starting substances A + B C + D Products Substances formed A + B C + D yields, produces reversible reaction, equilibrium (s) solid (l) liquid (g) gas (aq) aqueous (dissolved in water) coefficient number in front of a substance that indicates moles or units subscript number in a formula that indicates # of atoms (or polyatomic ions) heat is used in a reaction
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notes4 - Unit 4 Chemical Reactions Physical change: a...

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