TOPIC: Predicting amounts of reagents needed or

amounts of products made

Do Now:

Coefficients in Chemical Equations• Numbers in front ofin front of formulas called coefficients

– Microscopic: Coefficients represent numbers of individual atoms or molecules

– Macroscopic: Coefficients give mole ratios!– Moles connected to mass

Coefficients in Balanced EquationsMOLE-MOLE word problems: convert from

moles of one substance to moles of another substance

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

2 C2 C22HH66 + 7 O2 4 CO4 CO22 + 6 H2O

How much COCO22 will be produced if 4 moles of CC22HH66 are consumed?

4 moles C2H6= X moles CO2

X = 8 moles CO2

2 C2 C22HH66 + 7 O2 4 CO2 + 6 H6 H22OO

How much HH22OO will be produced in the combustion of 5 moles of CC22HH66?

5 moles C2H6= X moles H2O

X = 15 moles H2O

2 C2 C22HH66 + 7 O7 O22 4 CO2 + 6 H2O

How much oxygenoxygen will react with 5 moles of CC22HH66?

5 moles = X moles

X = 17.5 moles O2

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) doesn’t matter as long as

constant throughout

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

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

_________

15 L N2(g)=

X L H2(g)

_________

X = 45 L H2(g)

1

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

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

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

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

1.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