Chemistry Reading Supplemental Text Materials pages 173 185 Chemical Equations C O2 CO2 C s O2 g CO2 g Reactants on left products on right Each are balanced because same number of atoms of reactants as products Balancing Chemical Equations Molecules of reactants and products shown Cannot change the molecule Can change how many of them Cannot add or delete reactants or products Balanced equal number of same atoms on each side Water balancing Water balancing Water balancing Water balancing Rusting of Iron Fe O2 Fe2O3 not balanced start with oxygen Fe 3 O2 2 Fe2O3 next do iron 4 Fe 3 O2 2 Fe2O3 Problem 1 in class Balance the following equation on the sheet worksheet provided Put your name on the back of the sheet please N2 H2 NH3 N2 H2 NH3 N2 H2 NH3 fix hydrogen N2 3 H2 2 NH3 When H is fixed N is already done Combustion of methane CH4 O2 CO2 H2O fix hydrogen CH4 O2 CO2 2 H2O need more O reactants CH4 2 O2 CO2 2 H2O Now check to see if you are done Problem 2 in class Balance the following chemical equation the combustion of propane C3H8 O2 CO2 H2O C3H8 O2 CO2 H2O C3H8 O2 CO2 H2O fix carbon C3H8 O2 3 CO2 H2O Work on hydrogen C3H8 O2 3 CO2 4 H2O Now there are 10 oxygen on right C3H8 5 O2 3 CO2 4 H2O Poly atomic Groups SO4 is sulfate common 2 ionic group PO4 is Phosphate 3 ion OH is Hydroxyl 1 ion Combine with positive ions to balance charges to zero as a group Ca3 PO4 2 Ca is 2 Poly atomic Groups H2SO4 NaCN HCN Na2SO4 Fix sodium first H2SO4 2 NaCN HCN Na2SO4 Now Carbon and Nitrogen not balanced H2SO4 2 NaCN 2 HCN Na2SO4 This also fixes the Hydrogen SO4 is fine Poly atomic Groups H3PO4 Ca OH 2 Ca3 PO4 2 H2O H3 PO4 Ca OH 2 Ca3 PO4 2 H2O H3 PO4 3 Ca OH 2 Ca3 PO4 2 H2O 2H3 PO4 3 Ca OH 2 Ca3 PO4 2 H2O 2H3 PO4 3 Ca OH 2 Ca3 PO4 2 6H2O Volume Relationships Equal volumes of gases at the same temperature and pressure have the same number of molecules Gases react in small whole number quantities Avogadro s hypothesis chemicals react in consistent small whole number ratios Avogadro s hypothesis Combustion of propane C3H8 5 O2 3 CO2 4 H2O How much oxygen is needed to burn 0 556 L of propane Ratio of Oxygen molecules to propane molecules is 5 1 2 87 L Oxygen 0 556 L x 5 L O2 1 L Propane Problem 3 in class Combustion of propane C3H8 5 O2 3 CO2 4 H2O Calculate how much CO2 is produced when 2 L of propane is burned Combustion of propane C3H8 5 O2 3 CO2 4 H2O Ratio of CO2 to Propane 3 1 2 L Propane x 3 L CO2 1 L Propane 6 L CO2 Atomic vs Molecular Weight Atomic weight on periodic table is average of natural abundance of isotopes Atomic mass is the number of nucleons in a particular atom Molar mass is the mass of one mole of molecules One atomic mass number of grams 6 0221367x1023 molecules Calculate Molar Weight O atomic weight 15 9996 O 16 atomic mass 16 u Molecular oxygen O2 atomic mass 32 u Molecular O2 molar mass 32 g mole CO2 molar mass C 12 g mole O2 32 g mole CO2 12 32 44 g mole Problem 4 in class Calculate the molar mass of propane C3H8 assume molar mass of C 12 g mole assume molar mass of H 1 g mole Molar mass of propane C3H8 assume molar mass of C 12 g mole 3 C x 12 g mole 36 g mole assume molar mass of H 1 g mole 8 H x 1 g mole 8 g mole 8 36 44 g mole C3H8 Moles calculated from Grams Can find the molar mass of substance Na 23 g mole Multiply molar mass times moles 23 g mole x 0 250 moles 5 75 g Moles calculated from Grams Number of moles of 176 g of CO2 Molar mass of of CO2 44 g mole If you multiply you get a mess 176 g x 44 g mole results in units of g2 mole Alerts you that you made an error Moles calculated from Grams Number of moles of 176 g of CO2 Molar mass of of CO2 44 g mole Instead divide 176 g by 44 g mole Or look at it as 176 g x 1 mole 44 g 4 moles CO2 Problem 5 in class How many moles of Si 28 are there in 140 g of Si 28 Problem 5 in class How many moles of Si 28 are there in 140 g of Si 28 1 mole 140 g 28 g 5 moles Si
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