Multiple Choice
A sample of gas is collected over water at atmospheric pressure (patm = 1.00 atm). If the vapor pressure of water at the experimental temperature is 0.030 atm, what is the pressure of the dry gas (pgas)?
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7. Gases
The Ideal Gas Law Applications
Multiple Choice
Which of the following gases will absorb in the IR spectrum?
A
CO_2
B
N_2
C
H_2O
D
O_2
Verified step by step guidance1
Understand that for a molecule to absorb infrared (IR) radiation, it must have a changing dipole moment during its vibrational motions. This means the molecule must be IR active.
Recognize that diatomic molecules like N_2 and O_2 are homonuclear (consist of two identical atoms) and have no permanent dipole moment. Their vibrations do not change the dipole moment, so they are IR inactive.
Consider CO_2, which is a linear triatomic molecule. Although it is overall nonpolar, some vibrational modes (like the asymmetric stretch) cause a change in dipole moment, making CO_2 IR active.
Look at H_2O, a bent molecule with a permanent dipole moment. Its vibrational modes cause changes in dipole moment, so it strongly absorbs IR radiation.
Conclude that among the given gases, CO_2 and H_2O absorb in the IR spectrum due to their molecular structure and vibrational properties, while N_2 and O_2 do not.
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