ch 7 - Chem 100 Chapter 7 Chemical Reactions Evidence a...

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Anna Toy-Palmer 1 Chem 100 Chapter 7 – Chemical Reactions Evidence a chemical reaction Chemical equations and balancing them Solubility Precipitation reactions Molecular, Complete Ionic, and Net Ionic Equations Acid-base and Gas evolution reactions Oxidation-reduction reactions Classifying chemical reactions
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Anna Toy-Palmer 2 Chem 100 Evidence of a chemical reaction Precipitation reactions Gas formation Heat absorption or emission Light emission Color change Neutralizations that aren’t directly observable
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Anna Toy-Palmer 3 Chem 100 The chemical equation Represents a chemical reaction Consider this reaction: natural gas also known as methane reacts with oxygen when burning at a stove to form carbon dioxide and water. Molecular formulas: CH 4 , O 2 , CO 2 and H 2 O Arrow designates reaction Left side molecules are reactants (CH 4 and O 2 ) Right side molecules are products (CO 2 and H 2 O)
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Anna Toy-Palmer 4 Chem 100 Natural gas, methane, reacts with oxygen when burning at a stove, to form carbon dioxide and water. CH 4 (g) + O 2 (g) CO 2 (g) + H 2 O (g) We also need to designate the physical state of the reactants and products in a reaction (g) designates that the molecules are in gas form
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Anna Toy-Palmer 5 Chem 100 Abbreviations for states (g) gas (l) liquid (s) solid (aq) aqueous (water solution)
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Anna Toy-Palmer 6 Chem 100 Balancing the chemical equation CH 4 (g) + O 2 (g) CO 2 (g) + H 2 O (g) Number of atoms number of atoms 1 C 1 C 4 H 2 H 2 O 3 O Number of atoms is NOT balanced. Remember the Law of Conservation of Matter! Equation needs to be balanced
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Anna Toy-Palmer 7 Chem 100 CH 4 (g) + O 2 (g) CO 2 (g) + H 2 O (g) Equation needs to be balanced NEVER Change subscripts – this changes the compound Use Coefficients (changes the number of molecules)
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Anna Toy-Palmer 8 Chem 100 CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (g) Number of atoms number of atoms 1 C 1 C 4 H 4 H 4 O 4 O
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Anna Toy-Palmer 9 Chem 100 Another Example: 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + x O 2 Number of atoms number of atoms 6 C 6 C 12 H 12 H 18 O 6 O + x(2) Carbons and hydrogens are balanced To balance oxygen, we need x(2) = 12 x = 6
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10 Chem 100 Steps to balance a chemical equation 1. Write the skeletal equation 2. If an element occurs in only one compound on both sides of the equation, balance that first. If more than one, balance metals first, then nonmetals. 3. If an element occurs as a free element, do this one last. 4. If there are coefficient fractions, multiply by the appropriate factor to clear these out. 5.
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ch 7 - Chem 100 Chapter 7 Chemical Reactions Evidence a...

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