Vapor Pressure Examples: Common Substances and Their Vapor Pressures

📚 Quick Study Guide

• 🌡️ Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system.
• 📈 Vapor pressure increases with temperature. The relationship is described by the Clausius-Clapeyron equation: $\ln(P_2/P_1) = -\frac{\Delta H_{vap}}{R}(\frac{1}{T_2} - \frac{1}{T_1})$, where $P$ is pressure, $T$ is temperature, $\Delta H_{vap}$ is the enthalpy of vaporization, and $R$ is the ideal gas constant.
• 💧 Substances with high vapor pressures at room temperature are considered volatile (e.g., diethyl ether). Substances with low vapor pressures are non-volatile (e.g., ionic compounds).
• 🍶 Examples: Water (H₂O), Ethanol (C₂H₅OH), Diethyl Ether (C₄H₁₀O).
• 🌐 Standard pressure is defined as 100 kPa (kilopascals) or 1 atmosphere (atm).
• 🔢 Boiling point is the temperature at which the vapor pressure of a liquid equals the surrounding pressure. Normal boiling point is measured at standard pressure.

🧪 Practice Quiz

1. Which of the following substances has the highest vapor pressure at 25°C?
   1. A. Water
   2. B. Ethanol
   3. C. Diethyl Ether
   4. D. Acetic Acid


2. What happens to the vapor pressure of a liquid as its temperature increases?
   1. A. It decreases.
   2. B. It remains constant.
   3. C. It increases.
   4. D. It fluctuates randomly.


3. Which equation describes the relationship between vapor pressure and temperature?
   1. A. Boyle's Law
   2. B. Charles's Law
   3. C. Clausius-Clapeyron Equation
   4. D. Ideal Gas Law


4. A substance with a high vapor pressure is considered:
   1. A. Non-volatile
   2. B. Highly viscous
   3. C. Volatile
   4. D. Highly ionic


5. What is the standard pressure at which normal boiling point is measured?
   1. A. 50 kPa
   2. B. 200 kPa
   3. C. 100 kPa
   4. D. 150 kPa


6. Which of the following factors does NOT directly affect vapor pressure?
   1. A. Temperature
   2. B. Intermolecular forces
   3. C. Volume of liquid
   4. D. Type of liquid


7. Which substance would you expect to have the LOWEST vapor pressure at room temperature?
   1. A. Hexane
   2. B. Water
   3. C. Mercury
   4. D. Sodium Chloride