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When a chemical reaction occurs, there is ALWAYS a change in properties AND energy
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Color change Heat change Gas produced Precipitate formed
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Chemical Reactions - 3 min
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There are 5 basic types of chemical reactions:
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Two simple substances combine to form a more complex one. element + element compound
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Examples: 2H 2 + O 2 2H 2 O 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2
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A complex substance breaks into simple substances. compound element + element
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Examples: 2H 2 O 2H 2 + O 2 2KClO 3 2KCl + 3O 2
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A single element replaces an element in a compound. element + compound
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Example: Zn + 2HCl H 2 + ZnCl 2
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Two different elements in two different compounds switch places. compound + compound
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Example: H 2 SO 4 + 2NaOH Na 2 SO 4 + 2HOH
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A hydrocarbon reacts with oxygen to form carbon dioxide and water.
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Example: CH 4 + O 2 CO 2 + H 2 O
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An acid and base react to form a salt and water acid + base salt + water
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Example: 2HCl + Mg(OH) 2 MgCl 2 + 2H 2 O
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Any reaction in which elements change oxidation number.
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Example: S + O 2 SO 2 0 0 -2
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Example: S + O 2 SO 2 0 0 -2 +4
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Aqueous reactions that involve the formation of a precipitate, an insoluble substance.
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Example: 2KI (aq) + Pb(NO 3 ) 2(aq) 2KNO 3(aq) + PbI 2(s) Physical State Symbols: (aq) = aqueous (g) = gas (s) = solid (cr) = crystal (l) = liquid
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Predicting Reaction Products
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Predicting Reaction Products
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Atoms can be neither created nor destroyed in ordinary chemical reactions...
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so there must be the same number of atoms on both sides of the equation.
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Subscripts represent the number of atoms in each molecule. 2H 2 O 2H 2 + O 2
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Coefficients represent the number of molecules. 2H 2 O 2H 2 + O 2
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To determine the total number of atoms, multiply the coefficient by the subscript. 2H 2 O 2H 2 + O 2
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H 2 SO 4 There are ___ atoms of hydrogen.
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H 2 SO 4 There are ___ atoms of hydrogen. 2
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H 2 SO 4 There are ___ atoms of oxygen.
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H 2 SO 4 There are ___ atoms of oxygen. 4
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Al 2 (SO 4 ) 3 There are ___ atoms of oxygen.
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There are ___ atoms of oxygen. 12 Al 2 (SO 4 ) 3
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2 Na 2 O 2 There are ___ atoms of sodium.
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There are ___ atoms of sodium. 4 2 Na 2 O 2
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2 Ca 3 (PO 4 ) 2 There are ___ atoms of phosphorus.
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4 2 Ca 3 (PO 4 ) 2 There are ___ atoms of phosphorus.
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2 Ca 3 (PO 4 ) 2 There are ___ atoms of oxygen.
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16 2 Ca 3 (PO 4 ) 2 There are ___ atoms of oxygen.
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6 CaSiO 3 There are ___ atoms of calcium.
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6 There are ___ atoms of calcium. 6 CaSiO 3
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Balancing equations by inspection
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The order in which these seven steps are performed is important.
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While there ARE shortcuts, and you will learn about one,...
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following these steps in order is the best way to be sure you are correct.
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Check for diatomic molecules. H 2 - N 2 - O 2 - F 2 - Cl 2 - Br 2 - I 2
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Balance the Metals DO NOT include H x
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Balance the Nonmetals DO NOT include O x
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Balance Oxygen
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Balance Hydrogen
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Recount All Atoms This is done to find any counting mistakes!
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Recount All Atoms If the atoms are NOT balanced, there is a problem somewhere. Work your way back up the steps, from bottom to top, until you find the problem and fix it.
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If every coefficient in the equation will reduce, rewrite the equation with reduced coefficients.
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If there is a coefficient of 1 - the equation cannot be reduced.
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Balancing Equations
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