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Chemical Reactions. February 21, 2002. Evidence for Chemical Reactions. Color change Precipitation Gas production Changes in temperature Changes in properties. Chemical Equations. A shorter, easier way to showing chemical reactions using symbols instead of words
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Chemical Reactions February 21, 2002
Evidence for Chemical Reactions • Color change • Precipitation • Gas production • Changes in temperature • Changes in properties
Chemical Equations • A shorter, easier way to showing chemical reactions using symbols instead of words • Chemical Formula – shows the ratio of elements in a compound • H2O • NaCl • CO2
Structure of an Equation • Reactants – materials you start with • Products – materials you end with • Reactant + Reactant Product • H2 + O2 H2O2
Conservation of Mass • The amount of matter in a chemical reaction does not change, so the total mass of the reactants must equal the total mass of the products
Classifying Chemical Reactions • Synthesis • Decomposition • Single Replacement • Double Replacement
Synthesis • Two or more elements combine to form a more complex compound • A + B AB • Hand + kerchief handkerchief • Example: C + Cl2 CCl4
Decomposition • Breaks down compounds into simpler substances • AB A + B • Schoolbook school + book • Example: Al2O3 Al + O2
Replacement • A reaction in which one element replaces another in a compound, or two elements in different compounds trade places • AB + C AC + B (Single) • AB + CD AC + BD (Double) • T.V. screen + door knob T.V. knob + screen door • HCl + NaOH H2O + NaCl