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AP CHEM CHAPTER TEN LIQUIDS AND SOLIDS

Submitted by lp71223 on Mon, 09/24/2012 - 21:57

Iodine, like most substances, exhibits only three phases; solid, liquid, and vapor. The triple point of iodine is at 90 torr and 115 degrees Celcius. Which of the following statements concerning liquid I2 must be true? Explain your answer.

a.) I2 (l) is more dense than I2 (g).

b.) I2 (l) cannot exist above 115 degrees Celcius.

c.) I2 (l) cannot exist at 1 atmosphere pressure.

d.) I2 (l) cannot have a vapor pressure greater than 90 torr.

e.) I2 (l) cannot exist at a pressure of 10 torr.


look at this phase diagram for CO2 but you can get fair idea. 
http://cwx.prenhall.com/petrucci/mediali…

you may replace  -56.7 on the x-axis with 115°C and 5.1 atm on the y-axis with 90 torr .


Triple point is marked "O" on the graph and indicates the point where all three phases are present.

for part (a) below 90 torr, there is no liquid phase regardless of temperature ,either  you have solid or gas. the curve between the solid and gas phases is where the substance undergoes "sublimation" or "deposition" which actually depends on the direction. So 'TRUE'!

(b) look at any point in the gas phase that has temperature > 115°C. basically, look at the curve from O to C and move horizontally right. You'll see pressure can be > 90torr. So this statement is FALSE

(c)The liquid phase exists vertically upward of that curve from O to C and right of OD curve and left of the verticle line showing supercritical fluid. Notice it still exists as pressure increases.So, saying that I2(l) cannot exist at 760torr (1atm)  is FALSE


(d).True as gases are ALWAYS less dense than liquids.

(e) The melting point of iodine is 113.7°C and boiling point is 184.3°C. those are "normal" mp and bp and that means they are measured at 1atm pressure. ie.. at temps between 113.7°C and 184.3°C and P = 1atm, I2 is in the liquid phase.This is FALSE. see my answer to (c).


the correct choices are A and D