Kotz 4 Equa_Stoi lecture

Kotz 4 Equa_Stoi lecture - Writing and Balancing Chemical...

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1 Chemical Equations and Stoichiometry Topics: Equation Writing and Balancing Stoichiometry Coefficients Mass-Mole Relationships Limiting Reagents Percent Yield Quantitative Analysis Combustion (Revisited) Titration / Mineral Analysis Reactants Products (e.g. A + B C + D) Mass must be conserved in the chemical reaction (Conservation of Mass – Antoine Lavoisier) The number and type of atoms on each side of the reaction equation must be balanced. Chemical equations MUST be balanced by coefficients. Once the chemical formulas for the reactants and products are determined you MUST NOT change any subscripts, nor can you balance the equation by putting coefficients in the MIDDLE of a compound. Writing and Balancing Chemical Equations Formation of a Molecular Compound Formation of an Ionic Compound Coefficients multiply through to every element in the compounds. Ex. CaO (s) + 2NH 4 Cl (s) 2NH 3(g) + H 2 O (g) + CaCl 2(s) In the product, the 2 in front of NH 3 affects both the N and the H; i.e. 2 N and 6 H Coefficients tell you the mole ratio NOT mass ratio of the reaction components. Ex. In the equation above; 1 mole of CaO reacts with 2 moles of NH 4 Cl to produce 2 moles of NH 3 , and 1 mole each of H 2 O and CaCl 2 All masses must be converted to moles before setting up mole ratios It is a good idea to take inventory on the elements in the reaction. The symbols (aq), (l), (g), (s) are used to designate aqueous, liquid, gas and solid, respectively. Practice Problems: Balance the Following Reactions ____BaCl 2(aq) + ____AgNO 3(aq) ____AgCl (s) + ____Ba(NO 3 ) 2(aq) ____SO 2(g) + ____CaCO 3(s) + ____O 2(g) ____CaSO 4(s) + ____CO 2(g) ___NiCO 3(s) + ___HNO 3(aq) ___Ni(NO 3 ) 2(aq) + ___ CO 2(g) + ____H 2 O (l) 2 2 2 2 2 2 2
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2 Often you may have to translate a description of the reaction into a chemical reaction equation before balancing. Sample Problems: Write and balance the following reactions 1. Sodium phosphate reacts with calcium chloride to yield calcium phosphate and sodium chloride. 2. Copper and sulfuric acid react to yield cupric sulfate, water and sulfur dioxide. 2Na 3 PO 4 + 3CaCl 2 Ca 3 (PO 4 ) 2 + 6NaCl Cu + 2H 2 SO 4 CuSO 4 + 2H 2 O + SO 2 Stoichiometry: Mole-Mass Relationships Chemical reaction equations are written in terms of mole ratios. In order to solve quantitative problems using these equations,
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Kotz 4 Equa_Stoi lecture - Writing and Balancing Chemical...

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