Chem 116 Lecture 2

# Chem 116 Lecture 2 - STOICHIOMETRY the study of the...

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7/2/10 STOICHIOMETRY - the study of the quantitative aspects of chemical reactions.

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7/2/10 Mass reactant Stoichiometric factor Moles reactant Moles product Mass product General Plan for Stoichiometry Calculations
7/2/10 Molar mass (also called gram-molecular weight) Mass of 1 mole of chemical entities (atoms, ions, molecules, formula units) Described with units = g/mol Mass (g) = no. of moles x no. of grams 1 mol No. of moles = mass (g) x no. of grams 1 mol MASS(g) of element AMOUNT(mol) of element (g/mol) Interconverting Between Moles and Grams

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7/2/10 MASS(g) of element AMOUNT(mol) of element (g/mol) Interconverting Between Moles and Grams How many moles of H2O are in 42g of H2O? 1. Calculate molar mass of H2O. H = ______________________ O = Total = __________ 2. Calculate number of moles. ___________________= _________
7/2/10 Calculating amounts of reactants and products 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 + __ H2O

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7/2/10 454 g of NH4NO3 / N2O + 2 H2O STEP 2 Convert mass reactant (454 g) ° moles
7/2/10 454 g of NH4NO3 N2O + 2 H2O STEP 3 Convert moles reactant moles product Relate moles NH4NO3 to moles product expected. ______________________________________ Express this relation as the STOICHIOMETRIC FACTOR .

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7/2/10 454 g of NH4NO3 / N2O + 2 H2O = ______________________ STEP 3 Convert moles reactant ° moles product Use stoichiometric Factor
7/2/10 454 g of NH4NO3 / N2O + 2 H2O STEP 4 Convert moles product ° mass product Called the ___________________ ALWAYS FOLLOW THESE STEPS IN SOLVING STOICHIOMETRY PROBLEMS!

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7/2/10 454 g of NH4NO3° N2O + 2 H2O STEP 5 How much N2O is formed? Total mass of reactants = Total mass of products Note: Another way to solve is to convert moles of N2O formed to g
7/2/10 How many moles of oxygen are required to roast 10.0 mol of copper(I) sulfide?

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