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Offline butterwings

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vapor question
« on: October 28, 2009, 07:08:48 PM »
Which of the following are true statements ?

a) Volatiltiy of a liquid decreases with increasing temperature

b) The equilibrium vapor pressure of a liquid results from equal rates of evaporation and condensation

c) The equilibrium vapor pressure of a liquid changes with temperature

d) The vapor pressure of a liquid at its normal boiling point is strongly affected by the type of molecules the liquid consists of

please help me, I know that bd is correct. but i;m not too sure about a, someone told me it's true, and other said it's false. . i put abcd n it's incorrect, then i tried bcd and then i tried abc. please help me :[ thank you so much!
« Last Edit: October 28, 2009, 07:45:03 PM by butterwings »

Offline Dan

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Re: vapor question
« Reply #1 on: October 29, 2009, 08:38:06 AM »
i;m not too sure about a, someone told me it's true, and other said it's false. .

Here's a hint: When you take your clothes out of the washing machine and hang them out to dry, will they dry faster on a hot day or a cold day? So is the water more volatile at higher temperature or lower temperature?

I agree that b) is true.

Are you sure statement d) is correct?

Do you think c) is true or false (and why)?
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Offline jylxox

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Re: vapor question
« Reply #2 on: October 30, 2009, 01:07:11 AM »
Alight, so:
 A is correct b/c increasing temperature increases the amount of volatile liquid which vaporizes
 B is correct b/c an equilibrium is defined as the case where the "forward rate" is equal to the "reverse rate", since they are equal the statement is true.
 C is false b/c vapor pressure is a function of T. Increases in T result in increases in vapor pressure?  --> not sure if this is right
 Shouldn't D be correct though? boiling point is affected by the intermolecular attraction between the molecules and that depends on the molecules themselves.

however, as I plugged a,b,d it came out to be wrong. =/ Not sure whats wrong, b/c I tried different combinations already.

Offline Dan

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Re: vapor question
« Reply #3 on: October 30, 2009, 07:24:46 AM »
Quote
Which of the following are true statements ?

a) Volatiltiy of a liquid decreases with increasing temperature
Alight, so:
 A is correct b/c increasing temperature increases the amount of volatile liquid which vaporizes

Read the question carefully!

Also, increasing temperature increases the volatility of a liquid NOT the amount of liquid. Matter cannot be created or destroyed.

Quote
B is correct b/c an equilibrium is defined as the case where the "forward rate" is equal to the "reverse rate", since they are equal the statement is true.

Yes

Quote
c) The equilibrium vapor pressure of a liquid changes with temperature
Quote
C is false b/c vapor pressure is a function of T. Increases in T result in increases in vapor pressure?  --> not sure if this is right

Again, READ THE QUESTION.

Quote
Shouldn't D be correct though? boiling point is affected by the intermolecular attraction between the molecules and that depends on the molecules themselves.

Start by looking up the definition of "normal boiling point".
My research: Google Scholar and Researchgate

Offline typhoon2028

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Re: vapor question
« Reply #4 on: October 30, 2009, 11:48:09 AM »
"Here's a hint: When you take your clothes out of the washing machine and hang them out to dry, will they dry faster on a hot day or a cold day? So is the water more volatile at higher temperature or lower temperature?"

This is not always true, you did not include your assumptions about humidity.

d) The vapor pressure of a liquid at its normal boiling point is strongly affected by the type of molecules the liquid consists of

If you have three liquids each at their normal boiling point temperatures, they will exert the same vapor pressure.  At 760 mmHg, water boils at 100 C.  At 100 C the vapor pressure of water = 760 mmHg.

Offline Dan

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Re: vapor question
« Reply #5 on: October 30, 2009, 12:55:56 PM »
This is not always true, you did not include your assumptions about humidity.

True, it was a simplified example. I was assuming constant humidity, wind speed, pressure, amount of water on the wet clothes etc. etc. The only variable I intended in the example was temperature.
My research: Google Scholar and Researchgate

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