AIM # 2: How does temperature affect the vapor pressure of a liquid?

Vaporization: Liquid to Gas

Condensation: Gas to Liquid

1. DYNAMIC EQUILIBRIUM FIGURE # 1 FIGURE #2 FIGURE # 3

Molecules are constantly changing phase: “Dynamic” Rate of Vaporization = Rate of Condensation Molecules are constantly changing phase: “Dynamic” The amount of liquid and vapor remains constant: “Equilibrium”

2. The gas that is above the liquid is called its vapor and it creates a pressure called vapor pressure.

3. The boiling Point of a Liquid The boiling point (bp) is the temperature at which the vapor pressure of the liquid is just equals the atmospheric pressure. VAPOR PRESSURE = ATMOSPHERIC PRESSURE

4. See Table A: Units for Pressure at STP

5. Factors That Affect Equilibrium Vapor Pressure (Table H) A. Temperature B. Intermolecular forces

A. The vapor pressure of a liquid varies with its temperature

  The vapor pressure is relatively high when the evaporation rate is high. As the temperature of a given liquid increases, so does its rate of evaporation and so does its vapor pressure

B. The stronger the forces between the particles the higher the boiling point.

In CO2(s) the intermolecular forces are weak In CO2(s) the intermolecular forces are weak. Therefore, vapor pressure is high

Nonburning Dollar Bill

See Table H Intermolecular attraction are strongest in ethanoic acid (acetic acid), next strongest in water, third strongest in ethanol and weakest in propanone. Thus, we can use vapor pressures as indications of relative strengths of the attractive forces in liquids.

In H2O (s) intermolecular forces are strong In H2O (s) intermolecular forces are strong. Therefore, vapor pressure is low

What property of ethyl alcohol makes it volatile? So ethanol is volatile, because it is a small and light molecule. The intermolecular forces are weak

Volatile (Table H) A liquid with a high vapor pressure at a given temperature is said to be volatile.

Volatile? Readily vaporizing at a relatively low temperature.

Why is the boiling point lower in Denver, CO than in San Francisco, CA??

Denver is at a higher altitude where the atmospheric pressure will be lower. Therefore the vapor pressure will be lower.

The liquid boils at lower temperature The normal boiling point of water is 100oC. The term normal refers to standard pressure 101.3 kPa. LOCATION PRESSURE BOILING POINT OF WATER SEA LEVEL 101.3 KPa 100 ºC MT. EVEREST 34 kPa 70 ºC The liquid boils at lower temperature

At high altitudes (up in the Mountains) the air pressure is less than at sea level. Thus, water will boil at a lower temperature (the vapor pressure needed to support a bubble is lower at high altitude). Therefore, cooking times are longer for things that need to be boiled (e.g. boiled eggs take longer to cook at high altitudes).

Changing the Boiling Point Raise the external pressure (Use a pressure cooker) Raises the vapor pressure needed. Harder to make bubbles Raises the boiling point. Food cooks faster.

Highest 10 Mountains in the world Mountain peak Range Location Height (m) Everest Himalayas Nepal/Tibet 8,850 K2 Karakoram Pakistan/China 8,611 Kanchenjunga India/Nepal 8.586 Lhotse I 8,516 Makalu I 8,463 Cho Oyu 8,201 Dhaulagiri Nepal 8,167 Manaslu I 8,163 Nanga Parbat Pakistan 8,125 Annapurna 8,091

END OF THE SHOW!