Download Ch. 11: Gas Stoichiometry

Gay Lussac’s law of combining
volumes of gases
• When gases combine, they combine in
simple whole number ratios.
• These simple numbers are the coefficients
of the balanced equation.
N2 + 3H2
2NH3
• 3 volumes of hydrogen will produce 2
volumes of ammonia
Mullis
1
Avogadro’s Law and Molar Volume of Gases
• Equal volumes of gases (at the same temp and
pressure) contain an equal number of
molecules.
In the equation for ammonia formation,
1 volume N2 = 1 molecule N2 = 1 mole N2
• One mole of any gas will occupy the same
volume as one mole of any other gas
• Standard molar volume of a gas is the
volume occupied by one mole of a gas at STP.
Standard molar volume of a gas is 22.4 L.
Mullis
2
Sample molar volume problem
• A chemical reaction produces 98.0 mL of sulfur
dioxide gas at STP. What was the mass, in
grams, of the gas produced?
***Turn mL to L first! (This way, you can can use 22.4 L)
98 mL 1 L
1000 mL
1 mol SO2 64.07g SO2 = 0.280g SO2
22.4 L
1 mol SO2
Mullis
3
Sample molar volume problem 2
What is the volume of 77.0 g of nitrogen dioxide
gas at STP?
77.0 g NO2 1 mol NO2
22.4 L
46.01g NO2 1 mol NO2
Mullis
= 37.5 L NO2
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Ideal Gas Law
• Mathematical relationship for PVT and number of
moles of gas
PV = nRT
n = number of moles
R = ideal gas constant
P = pressure
V = volume in L
T = Temperature in K
R = 0.0821 if pressure is in atm
R = 8.314 if pressure is in kPa
R = 62.4 if pressure is inMullis
mm Hg
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Sample Ideal Gas Law Problem
• What pressure in atm will 1.36 kg of N2O gas exert
when it is compressed in a 25.0 L cylinder and is
stored in an outdoor shed where the temperature can
reach 59°C in summer?
V = 25.0 L T = 59+273 = 332 K P = ?
R = 0.0821L-atm
n = 1.36 kg converted to moles
mol-K
• 1.36 kg N2O 1000 g 1 mol N2O = 30.90 mol N2O
1 kg
44.02 g N2O
• PV = nRT
• P = 30.90 mol x 0.0821 L-atm x 332 K = 33.7 atm
25.0 L
mol-K
Mullis
6
Volume-Volume Calculations
• Volume ratios for gases are expressed the
same way as mole ratios we used in other
stoichiometry problems.
N2 + 3H2
2NH3
Volume ratios are:
2 volumes NH3 3 volumes H2 2 volumes NH3
3 volumes H2 1 volume N2 1 volume N2
Mullis
7
Sample Volume-Volume Problem
• How many liters of oxygen are needed to
burn 100 L of carbon monoxide?
2CO + O2
2CO2
100 L CO 1 volume O2
2 volume CO
Mullis
= 50 L O2
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Sample Volume-Volume Problem 2
Ethanol burns according to the equation below.
At 2.26 atm and 40° C, 55.8 mL of oxygen are
used. What volume of CO2 is produced when
measured at STP?
C2H5OH + 3O2
2CO2 + 3H2O
Number moles oxygen under these conditions is?
PV = nRT: 2.26 atm(.0558L) = n = 0.0049 mol O2
(0.0821 L-atm)(313K)
mol-K
0.0049 mol O2 2 mol CO2 22.4 L =0.073 L CO 2
3 mol O2 1 mol CO2
Mullis
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