Intermolecular forces and phase diagrams Ms. Hoang ACP Chemistry

review Name three intermolecular forces in the order of strongest to weakest _________________________________ Intramolecular forces (aka chemical bonds) are stronger/weaker than intermolecular forces Intermolecular forces are responsible for the chemical/physical properties of a compound

Three phases Phases Solid: fixed shape and volume Liquid: fixed volume but takes shape of container Gas: no definite volume or shape

Phases

Phase changes What kind of process is this (hint: think energy) _____________: Solid  Liquid _____________: Liquid  Gas _____________: Solid  Gas _____________: Gas  Liquid _____________: Liquid  Solid _____________: Gas  Solid What kind of process is this (hint: think energy) __________________ What kind of process is this (hint: think energy) __________________

Dynamic equilibrium Rate of phase changes are all equal States of Matter PhET Rate of phase changes are all equal

Vapor Pressure Vapor Pressure: the pressure exerted by a vapor in equilibrium with its liquid phase at a certain temperature HIGH vapor pressure volatile weak/strong intermolecular forces?

Practice problems Which substance is MORE volatile? Why? H2O vs. H2S H2O vs NaCl CH4 vs HCl

Boiling point and vapor pressure What is happening when water boils? H2O molecules need enough energy to break intermolecular forces and go from liquid to gas Can water boil at temperature other than 100oC?

Vacuum pump demo Youtube video: https://www.youtube.com/watch?v=glLPMXq6yc0

Heating curve for water q=mc∆T Temperature

Phase/phase changes depends on two variables Summary Phase/phase changes depends on two variables ________________________

Phase diagram Graph showing Temperature and Pressure at which different phases are in equilibrium Label phases: Solid, Liquid, Gas Triple Point: where all three phases are in equilibrium Critical Point: where gas and liquid phases become indistinguishable Critical pressure: pressure above which the liquid phase of a substance cannot exist Critical temperature: temp above which gas cannot be liquified Normal freezing point: temperature at which substance changes phase to a solid at P=1atm Normal boiling point: temperature at which vapor pressure of liquid = atmospheric pressure (1atm)