Chapter 3 - Chapter 3 Molecules, Moles, and Chemical...

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Chapter 3 Molecules, Moles, and Chemical Equations Dr. Manuel P. Soriaga Department of Chemistry The Language of Chemistry Chemical Symbols: Alphabets Chemical Formulas: Words Chemical Equations: Sentences Chemical Formulas and Equations Chemical formulas provide a concise way to represent chemical compounds. Chemical equations build upon chemical formulas to concisely represent a chemical reaction. Reactants are the original materials written on the left hand side of the equation: E.g.: C (s) + O 2(g) Products are the newly formed compounds written on the right hand side of the equation: E.g.: CO 2(g) Composition Stoichiometry: Relates elemental quantities in Chemical Formulas E.g.: H 2 O. H 2 O 2 Reaction Stoichiometry: Relates quantities of elements or compounds in Chemical Equations E.g.: 2H 2 + O 2 2H 2 O Stoichiometry The Hydrogen-Oxygen Reaction Chemical Equation: 2H 2(g) + O 2(g) 2H 2 O (g) Balancing Chemical Equations The Law of Conservation of Matter must be obeyed: The number of atoms of a given element on the reactant side must equal that on the product side. The chemical formulas of the reactants and products must be correct The subscripts in the formulas of reactants and products cannot be changed to balance the equations The numbers and kinds of atoms, and the charges must be conserved
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Balanced Chemical Equation Reactants Products Balanced Chemical Equation Balanced with respect to mass Balanced with respect to charge Numbers used to balance: stoichiometric coefficients Reactants Products 8H + (aq) + 3C 2 H 5 OH (l) + Cr 2 O 7 2– (aq) 2Cr 3+ (aq) + 3C 2 H 4 O (l) + 7H 2 O (aq) Balancing Chemical Equations: An Example Al + HCl AlCl 3 + H 2 Al + 3HCl AlCl 3 + H 2 Al + 3HCl AlCl 3 + 3 / 2 H 2 Balanced equation: 2Al + 6HCl 2AlCl 3 + 3H 2 Balancing Chemical Equations for Combustion Reactions For combustion reactions involving hydrocarbons, it is best to balance the C atoms first, then the H atoms, followed by the O atoms C 2 H 6 + O 2 CO 2 + H 2 O C 2 H 6 + O 2 2CO 2 + 3H 2 O C 2 H 6 + 7 / 2 O 2 2CO 2 + 3H 2 O 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O Treat polyatomic ion as a whole unit; do not break it up into its constituent atoms AgNO 3 + BaCl 2 Ba(NO 3 ) 2 + AgCl 2AgNO 3 + BaCl 2 Ba(NO 3 ) 2 + 2AgCl Balanced equation: 2AgNO 3 + BaCl 2 Ba(NO 3 ) 2 + 2AgCl Balancing Chemical Equations Involving Ionic Compounds Interpretation of Balanced Chemical Equations CH 4(g) + 2O 2(g) CO 2(g) + 2H 2 O (g) 1 molecule of methane (CH 4 ) reacts with 2 molecules of oxygen (O 2 ) to produce one molecule of carbon dioxide (CO 2 ) and 2 molecules of water (H 2 O) N A molecules of CH 4 reacts with 2 N A molecules of O 2 to produce N
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Chapter 3 - Chapter 3 Molecules, Moles, and Chemical...

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