Boiling Questions

[PeterPesto]

1. Vapor pressure is directly related to temperature, however values are recorded under a vacuum. When raising the temperature of water required for boiling, is the vapor pressure of water increasing with its temperature?

2. Also, the reason temperature stays constant is because the gas particiles carry away energy, and heat must be continually added to compensate. Is this correct?

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[Rabolisk]

For 1, yes.

 

[TXKnight]

1. Vapor pressure is directly related to temperature, however values are recorded under a vacuum. When raising the temperature of water required for boiling, is the vapor pressure of water increasing with its temperature?

2. Also, the reason temperature stays constant is because the gas particiles carry away energy, and heat must be continually added to compensate. Is this correct?

1-boiling point is when atmopheric pressure =vapor pressure. boiling points are recorded at 1 atm. so yes, vapor pressure increases w/ temp.

2-the energy transfer to the liquid is being used to break intermolecular forces by increasing the KE of the molecules (vibrational,rotational motion). I don't think vapor particles "carry away" any energy per se.

 

[NYR56]

2-the energy transfer to the liquid is being used to break intermolecular forces by increasing the KE of the molecules (vibrational,rotational motion). I don't think vapor particles "carry away" any energy per se.

I'm pretty sure that KE does NOT increase during a phase change, since the temperature does not change. The added energy is used to break bonds, not necessarily to increase the KE.

 

[Rabolisk]

Temperature as a measure of the average kinetic energy is really only valid for ideal gases. Not to mention there is some debate about what "kinetic energy" is (translational? rotational?). What we know is that temperature does not increase during phase changes.

 

[NYR56]

Temperature as a measure of the average kinetic energy is really only valid for ideal gases. Not to mention there is some debate about what "kinetic energy" is (translational? rotational?). What we know is that temperature does not increase during phase changes.

That may be true in reality, but for the MCAT, I'm pretty sure what I posted is what you should base your answers off of. The MCAT will make no distinction between KE for ideal gases and for other substances. Also, I believe answering that KE increases during a phase change will get you the wrong answer. Remember, the MCAT tests basic science knowledge, not controversial theories/topics, so keep it simple.