Characteristics of Gases. Vapor = term for gases of substances that are often liquids/solids under ordinary conditions Unique gas properties Highly compressible Inverse pressure-volume relationship Form homogeneous mixtures with other gases. Pressures of Enclosed Gases and Manometers.
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* Alternative unit for atmospheric pressure is 1 bar = 105 Pa
Answer: sulfur dioxide due to relative polarity and mass.
V1P1 = V2P2
V1 = V2
T , V
P1 = P2
V1P1 = V2P2
V1P1 = V2P2 V1 = V2 P1 = P2 V1P1 = V2P2
T1 T2 T1 T2 T1 T2
N2 + 3H2 2NH3
In the equation for ammonia formation,
1 volume N2 = 1 molecule N2 = 1 mole N2
Standard molar volume of a gas is 22.4 L.
***Turn mL to L first! (This way, you can can use 22.4 L)
98 mL 1 L 1 mol SO2 64.07g SO2 = 0.280g SO2
1000 mL 22.4 L 1 mol SO2
What is the volume of 77.0 g of nitrogen dioxide gas at STP?
77.0 g NO2 1 mol NO2 22.4 L = 37.5 L NO2
46.01g NO2 1 mol NO2
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 in mm Hg
V = 25.0 L T = 59+273 = 332 K P = ?
R = 0.0821L-atm n = 1.36 kg converted to moles mol-K
1 kg 44.02 g N2O
25.0 L mol-K
N2 + 3H2 2NH3
Volume ratios are:
2 volumes NH33 volumes H2 2 volumes NH3
3 volumes H2 1 volume N2 1 volume N2
2CO + O2 2CO2
100 L CO 1 volume O2 = 50 L O2
2 volume CO
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
0.0049 mol O2 2 mol CO2 22.4 L =0.073 L CO 2
3 mol O2 1 mol CO2
PV = nRT
MPV = MnRT
MP/RT = nM/V
MP/RT = mol(mass/mol)/V
MP/RT = density
M = dRT
1.00 mole of gas occupies 27.0 L with a density of 1.41 g/L at a particular temperature and pressure. What is its molecular weight and what is its density at STP?
M.W. = 1.41 g |27.0 L = 38.1 g___
L |1.0 mol mol
M = dRT d= M P = 38.1 g (1 atm)______________ = 1.70 g/L
P RT mol (0.0821 L-atm )(273K)
( mol-K )
OR…AT STP: 38.1 g | 1 mol = 1.70 g/L
mol | 22.4 L
A 0.371 g sample of a pure gaseous compound occupies 310. mL at 100. º C and 750. torr. What is this compound’s molecular weight?
n=PV = (750 torr)(.360L) = 0.0116 mole
RT 62.4 L-torr(373 K)
MW = x g_= 0.371 g = 32.0 g/mol
mol 0.0116 mol
Pt = P1 + P2 + P3 + …. + Pn
Pt = (n1 + n2 + n3 +…)RT/V = ni RT/V
P1 = X1P1 where X1 is the mole fraction (n1/nt)
ε = ½ mu 2 where m = mass of molecule
*Average is of the energies of individual gas molecules.
Just for fun: Link to mathematical details: http://user.mc.net/~buckeroo/MXDF.html
Lighter gases have higher speeds than heavier ones, so diffusion and effusion are faster for lighter gases.
r1 = M2
r1/r2 = u1/u2
Find the root-mean square speed of hydrogen molecules in m/s at 20º C.
1 J = 1 kg-m2/s2 R = 8.314 J/mol-K
R = 8.314 kg-m2/mol-K-s2
u2= 3RT = 3(8.314 kg-m2/mol-K-s2)293K
M2.016 g |1 kg___
u2= 3.62 x 106 m2/s2
u = 1.90 x 103 m/s
An unknown gas composed of homonuclear diatomic molecules effuses at a rate that is only 0.355 times that of O2 at the same temperature. What is the unknown gas?
rx = MO2 0.355 = 32.0 g/mol
rO2Mx 1 Mx
Square both sides: 0.3552 = 32.0 g/mol
Mx = 32.0 g/mol = 254 g/mol Each atom is 127 g,
0.3552 so gas is I2
Where a and b are empirical constants.
P + n2a (V – nb) = nRT