LiquidVapor Equilibrium Intermolecular Forces and Liquids and Solids

Liquid-Vapor Equilibrium (Intermolecular Forces and Liquids and Solids) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Write an equation for the equilibrium between liquid water and its vapor: Is evaporation an endothermic or exothermic process? Condensation Focus on Evaporation and Condensation Evaporation Least Order Greatest Order 11. 8

Before Evaporation At Equilibrium 11. 8

The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation H 2 O (l) H 2 O (g) Dynamic Equilibrium Rate of condensation = Rate of evaporation 11. 8

Factors affecting the vapor pressure • SURFACE AREA increasing surface area only means equilibrium is reached faster • TEMPERATURE

What is the name of this diagram? Why is it important? T 2 > T 1 11. 8

Vapor Pressure Versus Temperature Patterns? Why? 11. 8

Enthalpy of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid at its boiling point. Enthalpy of vaporization : physical process (phase change) as ___________: chemical reaction 11. 8

The relationship between vapor pressure and temperature can be expressed mathematically – NOT req’d by IB Clausius-Clapeyron Equation ln P = - DHvap RT + C P = (equilibrium) vapor pressure T = temperature (K) R = gas constant (8. 314 J/K • mol) C = integration constant Vapor Pressure Versus Temperature 11. 8

Heating Curve Why are there plateaus on this graph? 11. 8

The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure. The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm. 11. 8

What are three primary intermolecular forces? List in order of increasing strength.

The boiling point and enthalpy of vaporization are influenced by intermolecular forces… Compound Enthalpy of vaporization in k. J mol-1 Boiling Point in K 9. 0 109 methoxy methane 27. 2 248 ethanol 38. 6 352 methane CH 4 CH OCH 3 3 CH CH OH 3 2 Intermolecular Forces

State the relationship between intermolecular forces and enthalpy of vaporization. State the relationship between intermolecular forces and boiling point.

A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas. Phase Diagram of Water 11. 9

Effect of Increase in Pressure on the Melting Point of Ice and the Boiling Point of Water 11. 9