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# Vapor Pressure vs Temperature **Substances and Normal Boiling Points:** * diethylether: 34.6 °C * water: 100 °C * ethylene glycol: 197.3 °C **Observations:** * **Pressure Generated:** All three liquids generate pressure at 25°C. * **Highest Vapor Pressure:** Diethylether has the highest vapor...

# Vapor Pressure vs Temperature **Substances and Normal Boiling Points:** * diethylether: 34.6 °C * water: 100 °C * ethylene glycol: 197.3 °C **Observations:** * **Pressure Generated:** All three liquids generate pressure at 25°C. * **Highest Vapor Pressure:** Diethylether has the highest vapor pressure, indicating weaker intermolecular interactions. **Functional Form of the Curves:** * **Question:** What is the functional form of the curves? * **Answer:** The curves are exponential. They can be linearized by taking the natural logarithm (ln). **Clausius-Clapeyron Equation:** The relationship between vapor pressure and temperature is described by the Clausius-Clapeyron equation: $\ln P_{vap} = -\frac{\Delta H_{vap}}{RT} + C$ Where: * $P_{vap}$ is the vapor pressure * $\Delta H_{vap}$ is the enthalpy of vaporization * $R$ is the ideal gas constant (8.31451 J/K⋅mol) * $T$ is the temperature in Kelvin * $C$ is a constant **Determining Enthalpy of Vaporization:** * Enthalpy of vaporization ($\Delta H_{vap}$) can be determined by measuring vapor pressure as a function of temperature. * This relationship is related to bond energy and describes the transition from the molecular to bulk level. **Important Note:** The image indicates that temperature ($T$) needs to be in Kelvin for the Clausius-Clapeyron equation.