Investigating the Phase of High Entropy. Pressure

Transcription

1 Name: Investigating the Phase of High Entropy Do Now: Define atmosphere: What gases make up the atmosphere? What factors most strongly affect the weather? and Pressure A pressure gauge records a pressure of 450 kpa. Convert this measurement to atmospheres Practice Problems: Convert 2.6 atm into kilopascal.

2 Types of Pressures Atmospheric Pressure Vapor Pressure Gas Pressure Boiling Point Boiling Pt. at High Altitudes Boiling Pt. at Low Altitudes

3 Which liquid would evaporate first? Explain Why. Table H Vapor Pressure of Four Liquids An open glass of water left standing around will eventually evaporate even without being heated. When water evaporates, it changes from a liquid to a gas called water vapor. Water vapor takes up more space than an equal mass of liquid water. As a result, in a closed container, the vapor that forms can exert a significant amount of pressure. This pressure is known as vapor pressure. Even in an open container, the air pressing down on it confines the vapor. Some of it collects at the surface and exerts pressure. Occasional high-energy molecules at the water s surface escape. That is why the water eventually evaporates. But for water to expand and form vapor bubbles throughout the liquid as it does when it boils, the vapor has to exert as much pressure as the blanket of air confining it. As a liquid is heated, more of it turns into vapor and the vapor pressure increases. When the vapor pressure reaches atmospheric pressure, the liquid boils. Statement #1: Molecules remain as a liquid as long as the intermolecular forces between molecules are strong enough to hold them together and not let them escape the surface into the vapor phase. Questions 1. Which compounds, those with strong or weak intermolecular forces, are more likely to enter the vapor phase? 2. Which compounds, those with strong or weak intermolecular forces, will result in higher vapor pressure? 3. Which compound in Table H has the weakest intermolecular forces of attraction? 4. Which compound in Table H has the strongest intermolecular forces of attraction? 5. Explain, in terms of intermolecular forces, why ethanoic acid has a lower pressure than water.

4 6. Which unit is used to express the pressure of a gas? (1) mole (2) joule (3) kelvin (4) pascal 7. At 50. C and standard pressure, intermolecular forces of attraction are strongest in a sample of (1) ethanoic acid (2) ethanol (3) propanone (4) water 8. At standard pressure, CH4 boils at 112 K and H2O boils at 373 K. What accounts for the higher boiling point of H2O at standard pressure? (1) covalent bonding (2) hydrogen bonding (3) ionic bonding (4) metallic bonding Statement #2: Boiling occurs when the vapor pressure of a liquid equals the atmospheric pressure. Questions: 1. What is the value of standard pressure (atmospheric pressure at sea level) in units of kilopascal and atmospheres? kpa atm 2. At standard pressure (atmospheric pressure), what temperature does each of the four liquids boil? propanone water ethanol ethanoic acid 3. If the atmospheric pressure was reduced to 80 kpa, what temperature would each liquid boil at? propanone water ethanol ethanoic acid 4. Using your glossary, define the term volatile. 5. Which liquid on Table H would be described as most volatile? Explain why in terms of intermolecular forces of attraction.

5 State a general relationship between temperature and vapor pressure based on the diagram. Use Table H to answer the questions below. 1. Which of the four liquids have the lowest vapor pressure at 70 0 C? 2. Which liquid has the highest vapor pressure at 50 0 C? 3. At 65 0 C, which substance has a vapor pressure of 58kPa? 4. Which compound has a vapor pressure of 130kPa at a temperature of 64 0 C? 5. What is the vapor pressure of ethanoic acid at 90 0 C? 6. What is the vapor pressure of water at C? 7. Which of the four liquids has a boiling point of 79 0 C at standard pressure? 8. At what atmospheric pressure will propanone boil at 20 0 C? 9. At 70 kpa, determine the boiling point of each liquid: 0 C Propanone 0 C Ethanol 0 C Water 0 C Ethanoic Acid