Chapter 3_May11 - CHAPTER3 STOICHIOMETRY:...

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CHAPTER 3 STOICHIOMETRY: CALCULATIONS OF CHEMICAL  FORMULAS AND EQUATIONS
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CONTENTS 3.1 Chemical Equations 3.2 Chemical Reactivity 3.3 Atomic and Molecular Weights 3.4 The Mole 3.5 Empirical Formulas from Analyses 3.6 Quantitative Information from Balanced Equation 3.7 Limiting Reactants
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Learning Outcomes Able to calculate the molecular weight of any  given compound Able to calculate the amount of reactants or  products in mass or mole with information  given. To be able to identify the limiting reactant in a  given reaction formula of a compound from an analysis
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Introduction Stoichiometry – study of quantitative relationship between chemical formulas and chemical equations. The law of conservation of mass is observed : total mass of all substances present before the reaction (reactants) is the same as the total mass after the reaction (products).
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3.1 Chemical Equations Describe chemical reactions. Eg: 2H + O 2H 2 O This chemical equation shows that hydrogen
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Con’t: 3.1 Chemical Equations There are 2 types of number in a chemical equation: i. Stoichiometric coefficient - number in front of a chemical formula. ii. Subscripts – number of atoms of each element present in the chemical formula.
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Con’t: 3.1 Chemical Equations E.g: 2H 2 O: 2 water molecules present. H 2 O - there are 2H atoms in one molecule of water.
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3.1.1 Balancing Chemical Equations Formulas of the substances must be correctly written. The number of atoms of each type of element must be the same on both sides of the arrow. Only stoichiometric coefficients may be adjusted. Subscripts in chemical formulas must not be changed.
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Con’t: 3.1.1 Balancing Chemical Equations The sum of charges of ions on the left hand side of the arrow must be the same as on the right side. Balancing chemical equation requires some trial and error.
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Con’t: 3.1.1 Balancing Chemical Equations Eg. methane reacting with oxygen. CH 4 + O 2 CO 2 + H 2 O : this is unbalanced. o Firstly, balance the carbon and hydrogen atom without considering oxygen. CH 4 + O 2 CO 2 + 2H 2 O o Secondly, balance the oxygen atom. CH 4 + 2O 2 CO 2 + 2H 2 O
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Con’t: 3.1.1 Balancing Chemical Equations Finally, the physical state of each chemical in chemical equation should be written down. Use the symbols: (g) for gas (l) for liquid (s) for solid (aq) for aqueous (water) solution Eg: CH 4 (g) + O 2 (g) CO 2 (g) + 2H 2 O(l)
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Exercise 3.1 Balance the following equations: a) HNO 3 (aq) + Na 2 CO 3 (s) NaNO 3 (aq) + H 2 O (l) + CO 2 (g) b) HCl (aq) + Al(OH) 3 (aq) H 2 O(l) + AlCl 3 (aq) c) ZnS(s) + O 2 (g) ZnO(s) + SO 2 (g)
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3.2 Chemical Reactivity 3.2.1 Using the Periodic Table The pattern of chemical reactivity of elements varies systematically, using the Periodic Table. Eg. All alkali metal react with water as follows:
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Chapter 3_May11 - CHAPTER3 STOICHIOMETRY:...

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