Chapter_03-Stoichiometry - Chapter 3 Stoichiometry Chapter...

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Chapter 3. Stoichiometry Chapter 3. Stoichiometry Chemical Chemical equations equations 2H 2 + O 2 2H 2 O Chemical reaction Reactants Products Coefficient Example: burning of hydrogen in oxygen Chemical equation:
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Chapter 3. Stoichiometry Chapter 3. Stoichiometry Chemical Chemical equations equations Balancing chemical equations (simple cases) Balancing chemical equation means making the number of corresponding atoms equal from both sides. Example 1: burning of metane in oxygen: 1.CH 4 + O 2 CO 2 + H 2 O (unbalanced); 2.CH 4 + O 2 CO 2 + 2H 2 O (still unbalanced); 3.CH 4 + 2O 2 CO 2 + 2H 2 O (balanced). Result: One carbon, four hydrogen and four oxygen atoms are both among reactants (left side) and at products (right side). Example 2: oxydation of iron: 1. Fe + O 2 Fe 2 O 3 (unbalanced) 2. Fe + 3O 2 2Fe 2 O 3 (still unbalanced) 3. 4Fe + 3O 2 2Fe 2 O 3 (balanced) Result: Four iron and six oxygen atoms at both sides. Hint: It is good idea to start balancing those elements that are contained in the fewest number of formulas.
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Chapter 3. Stoichiometry Chapter 3. Stoichiometry Chemical Chemical equations equations Example: oxydation of butene by hydrogen peroxide 1.C 4 H 8 + H 2 O 2 CO 2 +H 2 O (unbalanced) 2.a*C 4 H 8 + b*H 2 O 2 c*CO 2 +d*H 2 O (balanced with unknown coefficients) Now we make several mathematical equations – balancing each element separately: For C: 4*a = c For H: 8*a + 2*b = 2*d For O: 2*b = 2*c + d …… Result: b=12*a; c=4*a; d=16*a; We arbitrary select the smallest coefficient a to be 1; Result of balancing: 3. C 4 H 8 + 12H 2 O 2 4CO 2 +16H 2 O (balanced) Balancing chemical equations (advanced)
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Chapter 3. Stoichiometry Chapter 3. Stoichiometry Chemical Chemical equations equations 1. Cu 2 O + 2CO 2 2CuO + CO 2. 2C 6 H 6 + 2HNO 3 + O 2 2C 6 H 5 NO 3 + 2H 2 O 3. 3 H 2 + 2N 2 2N H 3 Which reactions are not balanced?
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Chapter 3. Stoichiometry Chapter 3. Stoichiometry Chemical Chemical equations equations Possible states: Gas ( g ) Liquid ( lq ) Solid ( s ) Aqueous solution ( aq ) Indicating physical state in chemical equations Example: Precipitation of solid calcium carbonate: Na 2 CO 3 (aq) + CaCl 2 (aq) 2NaCl(aq) + CaCO 3 (s) Example: Release of carbon dioxide gas: Na 2 CO 3 ( aq ) + 2HCl( aq )
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