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Chapter 7. Chemical Reactions: An Introduction 7.1 Evidence for a Chemical Reaction Color change Formation of a solid Formation of a gas Change in temperature. 7.2 Chemical Equations Chemical Reaction - a chemical change occurs Chemical Equation Reactants Products
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Chapter 7. Chemical Reactions: An Introduction 7.1 Evidence for a Chemical Reaction Color change Formation of a solid Formation of a gas Change in temperature
7.2 Chemical Equations Chemical Reaction- a chemical change occurs Chemical Equation Reactants Products Law of Conservation of Matter (therefore, must balance) Example: hydrogen and oxygen make water Indicate physical states of reactants & products Solid (s) Liquid (l) Gas (g) Aqueous (aq) dissolved in water
Figure 7.4:The reaction between methane and oxygen. CH4 + O2 CO2 + H2O
7.3 Balancing Chemical Equations • Formulas must be written correctly FIRST! • (Don’t forget diatomic molecules!) • 2. You may not change subscripts on formulas in order to balance equations • 3. Use coefficients; it multiplies everything in the formula. • 3O2 = 6 O atoms total • 4NaOH = 4 Na atoms, 4 O atoms, 4 H atoms • ___N2 + ___H2 ___NH3 • ___C2H6 + ___O2 ___CO2 + ___H2O • ___H2 + ___O2 ___H2O • ___O2 ___O3 • ___Cl2 + ___NaBr ___NaCl + ___Br2