TOPIC: Predicting amounts of reagents needed or amounts of products made Do Now:

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TOPIC Predicting amounts of reagents needed or
amounts of products madeDo Now
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Coefficients in Chemical Equations

• Numbers in front of formulas called coefficients
  
• Microscopic Coefficients represent numbers of
  individual atoms or molecules
• Macroscopic Coefficients give mole ratios!
• Moles ? connected to mass

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Coefficients in Balanced Equations

• MOLE-MOLE word problems convert from moles of
  one substance to moles of another substance

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2 C2H6 7 O2 ? 4 CO2 6 H2O

• How much CO2 will be produced if 4 moles of C2H6
  are consumed?

1) Start with balanced chemical equation
2) Problem will ask how many moles/liters given
will yield certain amount something else
3) Use a proportion to compare old mole/liter
amounts to the new mole/liter amounts
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2 C2H6 7 O2 ? 4 CO2 6 H2O

• How much CO2 will be produced if 4 moles of C2H6
  are consumed?

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2 C2H6 7 O2 ? 4 CO2 6 H2O

• How much H2O will be produced in the combustion
  of 5 moles of C2H6?

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2 C2H6 7 O2 ? 4 CO2 6 H2O

• How much oxygen will react with 5 moles of C2H6?

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Gas-Phase Equations

• coefficients in equations represent
• ratio of volumes of gases involved in rxn
• volume-volume word problems
• rxns where ALL reactants products are gases
• volume unit (liter/milliliter) doesnt matter as
  long as constant throughout

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N2(g) 3 H2(g) ? 2 NH3(g)

• How much hydrogen gas will react with 15 liters
  of nitrogen gas?

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Mass-Volume Problems

• REMINDER 1 mole any gas occupies same volume as
  any other gas (At STP 22.4 L/mol)
• REMINDER 1 mole gram formula mass
• CO2 12 16 16 44 g/mol

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What volume of Cl2(g) measured at STP is produced
when 7.65g HCl (aq) reacts with MnO2

• MnO2(s) 4HCl(aq) ? MnCl2(aq) Cl2(g) 2H2O(l)
• 1. CONVERT TO MOLES
• 7.65g HCl mol .2125 mols HCl
• 36 g HCl
• 2. Set up ratio 4 1 .053125 mols Cl2
• .2125 X
• 3. Convert Moles to Liters
• .053125 mols Cl2 22.4 L 1.19 L
  
• 1 mol

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What mass of NH3(g) is produced when 2.15L of
H2(g) measured at STP reacts?

• 3H2(g) N2(g) ? 2NH3(g)
• Set up Ratio 3 2 1.43 L NH3
• 2.15 X

2. Convert L to Moles 1.43 L mol
.064 mol NH3 22.4 L
3. Convert Moles to grams .064 mol 17
g 1.09 g mol