CHEM 1040 Lecture Notes - Lecture 4: Triple Point, Phase Diagram

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26 Aug 2016

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Definition: temperature at which the vapor pressure is equal to the atmospheric pressure. Normal boiling point: the boiling point a 1 atmosphere. Ex: the boiling point in the mountains is lower than the boiling point on plain fields because the atmospheric pressure decreases as altitude increases. Critical temperature: the temperature above which its gas cannot be liquefied. Critical pressure: the minimum pressure needed to liquefy a substance at its critical temperature. Phase diagram: (see text book for picture) Co2 cannot exist in the liquid phase below 5. 2 atmosphere. Triple point: combination of pressure and temperature where three phase of a substance exist in equilibrium.

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Question 14

The vapor pressure of a substance describes how readily molecules at the surface of the substance enter the gaseous phase. At the boiling point of a liquid, the liquid's vapor pressure is equal to or greater than the atmospheric pressure exerted on the surface of the liquid. Since the atmospheric pressure at higher elevations is lower than at sea level, the boiling point of water decreases as the elevation increases. The atmospheric pressure at sea level is 760 mmHg. This pressure decreases by 19.8 mmHg for every 1000-ft increase in elevation.

Elevation Pressure 0 ft 760 mmHg

1000 ft 740.2 mmHg

2000 ft 720.4 mmHg

The boiling point of water decreases 0.05âC for every 1 mmHg drop in atmospheric pressure.

Question:

What is the boiling point of water at an elevation of 1.50Ã10⁴ ft ?

Express your answer with the appropriate units using three significant figures.

Â±Exercise 11.76 with feedback - PMM The vapor pressure of nitrogen at several different temperatures is shown below. Temperature (K) Pressure (torr) 65 130.5 85 1718 You may want to reference ( pages 499 - 509) Section 11.5 while completing this problem. Part A Use the data to determine the heat of vaporization, ÎHvap , of nitrogen using the two point form of the van't Hoff equation. This equation is known as the Clausius-Clapeyron equation when applied to the vaporization "reaction" of liquid phases. For this problem, the vaporization reaction is: N2(l)âN2(g) Express your answer in kilojoules per mole. ÎH = kJ/mol SubmitMy AnswersGive Up Part B Determine the normal boiling point of nitrogen. Remember that boiling points are temperatures, so you're finding the temperature at which the vapor pressure is equal to the atmospheric pressure which is the condition that must be met for boiling to occur. The normal boiling point defines atmospheric pressure to be 760 torr. So, you're finding the temperature at which the vapor pressure is equal to 760 torr. Express your answer in kelvins. T =

Which of the following statements is false?

The viscosity of a liquid decreases as temperature increases.

The vapor pressure of a substance increases as temperature increases.

The vapor pressure of a substance with strong intermolecular forces is greater than that of a substance with weak intermolecular forces (at the same temperature).

A substance boils when its vapor pressure is equal to the atmospheric pressure.

The boiling point of water increases as atmospheric pressure increases.

The half-life for a reaction that is first-order in A is 15 minutes. How long will it take for the concentration of A to change from 0.16 M to 0.040 M?

A(g) â B(g) + C(g)

		60 min
		45 min
		30 min
		23 min
		15 min

CHEM 1040 Lecture Notes - Lecture 4: Triple Point, Phase Diagram

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