chapter 12 stoichiometry goal 4 calculate quantities of reactants and products needed in chemical...
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Chapter 12
Stoichiometry
Goal Calculate quantities of reactants and
products needed in chemical rxns using balanced chemical equations.
Using an Equation as a Recipe
Ingredients: Frame, Seat, Wheels, Handlebar, Pedals
Balanced equation:
1F + 1S + 2W + 1H + 2P 1 FSW2HP2
How many pedals are needed to make 128 bicycles?
= 256 pedals128 FSW2HP2
1 FSW2HP2
2P
1F + 1S + 2W + 1H + 2P 1 FSW2HP2
Examining a Balanced Chemical Equation
2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(g) 2 moles of H2S reacts with 3 moles of O2 to
produce 2 moles of SO2 and 2 moles of H2O.
4 moles of H2S reacts with ___moles of O2
____ moles of O2 are needed to produce 7 moles of H2O
How to solve these is on the next slide.
610.5
= 6 mol O2
4 mol H2S
2 mol H2S
3 mole O2
Mole-Mole Ratio Problems
= 10.5 mol O2
7mol H2O
2 mol H2O
3 mole O2
The mol-mol ratio comes from the coefficients in the balanced equation. In the balance equation, O2 has a coefficient of 3, H2O has a coefficient of 2, and H2S has a coefficient of 2.
Mass-Mass Calculation
Write the balanced chemical equationLabel above the equation what you are
given and what you are trying to find.Convert grams of your given to moles using
molar massMultiply by the mole-mole ratio from the
balanced chemical equationConvert moles of unknown to grams
Bringing It All Together
How many grams of ammonia ( ) should be produced when 6.00g nitrogen react with excess hydrogen?
Solve: Write the balanced equation with the information labeled above it.
6.00 g excess ? g
N2 + 3H2 2 NH3
NH3
Bringing It All Together
Convert given to moles:
Multiply by the mole ratio:
= 0.428 mol NH3
= 0.214 mol N2
6.00g N2
28 g N2
1 mole N2
0.214 mol N2
1 mol N2
2 mol NH3
Wrapping It Up
Convert moles of unknown to grams:
= 7.28g NH3
Summary:When 6.00g of nitrogen(N2) reacts with an excess of Hydrogen (H2), 7.28g of ammonia (NH3)should be produced.
0.428 mol NH3
1 mol NH3
17g NH3
Now You Try!
What mass of aluminum is required to
completely react with 7.80g oxygen in a
synthesis reaction?
Write the balanced equation
4Al + 3O2 2Al2O3
Label your given and unknown information
4Al + 3O2 2Al2O3
7.80 g
Since you were not given info aboutthis compound,don’t worry about itand don’t use it.
NEXT?...
Convert given to moles:
Multiply by the mole ratio:
7.80g O2
32g O2
1 mol O2 = 0.244mol O2
0.244mol O2
3 mol O2
4 mol Al= 0.325 mol Al
AND FINALLY!!
Convert moles of unknown to grams:
0.325 mol Al
1 mol Al
27g Al= 8.78g Al
8.78g of aluminum (Al) should be required to react completely with7.80g of oxygen (O2) in the synthesis of aluminum oxide (Al2O3).
Mass-Volume Calculation Write the balanced chemical equation Label above the equation what you are given and
what you are trying to find. Convert grams of your given to moles using molar
mass Multiply by the mole-mole ratio from the balanced
chemical equation Convert moles of unknown to liters (a.k.a dm3)
using molar volume (22.4L/ 1mol)
Bringing It All Together
How many liters of oxygen are necessary for the combustion of 134g of magnesium, assuming the reactions occurs at STP?
Solve: Write the balanced equation with the information labeled above it.
134 g ? L
2Mg + O2 2 MgO
Bringing It All Together
Convert given to moles:
Multiply by the mole ratio:
= 5.514 mol Mg
= 2.757 mol O2
134g Mg
24.3 g Mg
1 mole Mg
5.514 mol Mg
2 mol Mg
1 mol O2
Wrapping It Up
Convert moles of unknown to liters:
= 61.8 L O2
61.8 L of O2 are required to completely combust 134g Mg in the synthesis of MgO.
2.757 molO2
1 mol O2
22.4 LO2
Volume-Mass Calculation
Write the balanced chemical equation Label above the equation what you are
given and what you are trying to find. Convert liters of your given to moles using
molar volume Multiply by the mole-mole ratio from the
balanced chemical equation Convert moles of unknown to grams using
molar mass
Bringing It All Together
Find the mass of sulfur (S8) required to react with oxygen to produce 2.47L of sulfur dioxide gas at STP.
Solve: Write the balanced equation with the information labeled above it.
? g 2.47L
S8 + 8 O2 8 SO2
Bringing It All Together
Convert given to moles:
Multiply by the mole ratio:
= 0.1103 mol SO2
= 0.01378 mol S8
2.47L SO2
22.4 L SO2
1 mole SO2
0.1103 mol SO2
8 mol SO2
1 mol S8
Wrapping It Up
Convert moles of unknown to grams:
= 3.53 g S8
3.53g of sulfur (S8) are required to produce2.47 L of sulfur dioxide (SO2).
0.01378 mol S8
1 mol S8
256g S8
Volume-Volume Calculations Write the balanced chemical equation Label above the equation what you are
given and what you are trying to find. Convert liters of your given to moles using
molar volume (22.4L/1mol) Multiply by the mole-mole ratio from the
balanced chemical equation Convert moles of unknown to liters using
molar volume (22.4L/1 mol)
Bringing It All Together
What volume of H2S gas is needed to produce 14.2 L of water at STP?
Solve: Write the balanced equation with the information labeled above it.
?L 14.2L
2H2S + 3O2 2 SO2 + 2 H2O
Bringing It All Together
Convert given to moles:
Multiply by the mole ratio:
= 0.6339 mol H2O
= 0.6339 mol H2S
14.2 L H2O
22.4 L H2O
1 mole H2O
0.6339 mol H2O
2mol H2O
2 mol H2S
Wrapping It Up
Convert moles of unknown to liters:
= 14.2 L H2S
14.2 L of H2S are required to produce 14.2 L H2O.
0.6993 mol H2S
1 mol H2S
22.4 LH2S
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