应用化学专业英语 教学课件 ppt 作者 黄忠 谢普会 付颖 主编lesson 24-25 chemical reactions and calculations.ppt

应用化学专业英语 教学课件 ppt 作者 黄忠 谢普会 付颖 主编lesson 24-25 chemical reactions and calculations.ppt

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Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O2(g) --- 2 Al2O3(s) The numbers in the front are called stoichiometric coefficients The letters (s), (g), and (l) are the physical states of compounds. Chemical Equations 4 Al(s) + 3 O2(g) --- 2 Al2O3(s) This equation means 4 Al atoms + 3 O2 molecules ---give--- 2 molecules of Al2O3 4 moles of Al + 3 moles of O2 ---give--- 2 moles of Al2O3 Chemical Equations Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change. The Law of the Conservation of Matter Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Balancing Equations ___ Al(s) + ___ Br2(liq) --- ___ Al2Br6(s) Balancing Equations ____C3H8(g) + _____ O2(g) ---- _____CO2(g) + _____ H2O(g) STOICHIOMETRY - the study of the quantitative aspects of chemical reactions. STOICHIOMETRY It rests on the principle of the conservation of matter. PROBLEM: If 454 g of NH4NO3 decomposes, how much N2O and H2O are formed? What is the theoretical yield of products? STEP 1 Write the balanced chemical equation NH4NO3 --- N2O + 2 H2O 454 g of NH4NO3 -- N2O + 2 H2O STEP 2 Convert mass reactant (454 g) -- moles 454 g of NH4NO3 -- N2O + 2 H2O STEP 3 Convert moles reactant -- moles product Relate moles NH4NO3 to moles product expected. 1 mol NH4NO3 -- 2 mol H2O Express this relation as the STOICHIOMETRIC FACTOR. 454 g of NH4NO3 -- N2O + 2 H2O = 11.4 mol H2O produced 454 g of NH4NO3 -- N2O + 2 H2O GENERAL PLAN FOR STOICHIOMETRY CALCULATIONS 454 g of NH4NO3 -- N2O + 2 H2O STEP 5 How much N2O is formed? Total mass of reactants = total mass of products 454 g NH4NO3 = ___ g N2O + 204 g H2O mass of N2O = 250. g 454 g of NH4NO3 -- N2O + 2 H2O STEP 6 Calcu

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