1. Lecture 0301 Chemical Equations and Reaction Types
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2. Law of Conservation of Mass
“We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends.”
--Antoine Lavoisier, 1789
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3. Practice Exercise 3.1
In the following diagram, the white spheres represent hydrogen atoms, and the blue spheres represent nitrogen atoms. To be consistent with the law of conservation of mass, how many NH3 molecules should be shown in the right box?
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4. Chemical Equations
Chemical equations are concise representations of chemical reactions, a Chemist’s Shorthand.
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5. Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
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6. Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Reactants appear on the left side of the equation.
© 2009, Prentice-Hall, Inc.

7. Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Products appear on the right side of the equation.
© 2009, Prentice-Hall, Inc.

8. Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
The states of the reactants and products are written in parentheses to the right of each compound.
© 2009, Prentice-Hall, Inc.

9. Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Coefficients are inserted to balance the equation.
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10. Subscripts and Coefficients Give Different Information
Subscripts tell the number of atoms of each element in a molecule.
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11. Subscripts and Coefficients Give Different Information
Subscripts tell the number of atoms of each element in a molecule
Coefficients tell the number of molecules.
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12. Practice Exercise 3.2
Balance the following equations by providing the missing coefficients:
(a) _Fe(s) + _O2(g) → _Fe2O3(s)
(b) _C2H4(g) + _O2(g) → _CO2(g) + _H2O(g)
(c) _Al(s) + _HCl(aq) → _AlCl3(aq) + _H2(g)
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13. Practice Exercise 3.2
Balance the following equations by providing the missing coefficients:
(a) _4Fe(s) + _3O2(g) → 2_Fe2O3(s)
(b) _1C2H4(g) + _3O2(g) → _2CO2(g) + 2_H2O(g)
(c) 2_Al(s) + 6HCl(aq) → 2_AlCl3(aq) + _3H2(g)
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