Unit 8 - liquids and solutions

Phases of Matter Phases of Matter? Temperature dependence? Phase Diagram - P vs T Triple point – point where all 3 phases are present (in equilibrium) critical point – point at which no increase in pressure will condense the gas normal bp & mp ( at 1 atm)

Phase Diagrams

Phase Diagram water

Phase Diagram carbon dioxide

Supercritical CO2 Video water gas to solid - triple point Video

Heating Curve

Energy Changes Heating Curve Molar heat of fusion – amount of energy needed to melt 1 mole of a substance Heat of vaporization – amount of energy needed to vaporize 1 mole of a substance Specific heat, Cp, – the amount of heat needed to raise 1 gram of a substance 1 oC Q = m x Cp x DT

Intra vs Intermolecular Forces - why molecules stick together - and/or under what conditions Intermolecular forces are those between molecules. Chemical bonds are intramolecular (within a molecule) forces. Intermolecular forces are as much as 5% of a chemical bond. These forces determine what state of matter exists at room temperature. What types of compounds are solids? liquids? gases?

Intermolecular forces What can cause molecules to stick to each other? Molecules have what type of bonding? Covalent bonding has atoms _____ electrons. Do atoms share electrons equally? What are molecules with unequally shared electrons? Polar molecules have permanent dipoles.

Intermolecular forces - 3 types Hydrogen bonding is strongest (actually just a special case of the dipole-dipole attraction. Dipole-dipole attraction - polar molecules are attracted to each other, the positive charge of one molecule to the negative charge of another molecule London Dispersion force is the weakest - non-polar molecules can have temporary dipoles

London dispersion force Balloon demo - Occurs in all molecules! But only important in nonpolar molecules. Caused by the motion of electrons. The more electrons the larger the force. F2 < Cl2 < Br2 < I2 The motion of e- s makes a non-uniform distribution - a temporary dipole. This then induces a dipole on another molecule - and they are attracted to each other. Balloon demo

dipole-dipole attraction

Hydrogen bonding in water

Hydrogen bonding in ice

Hydrogen bonding series graph

Evaporation & Vapor Pressure Intermolecular forces have what affect on Vapor Pressure?

much higher, ionic are solids Summary Chapter 14 Intermolecular Forces (why molecules stick to each other)   Type type of bonding boiling / melting point phase examples London-dispersion (LD) weakest no permanent charge nonpolar covalent very low gas H2 Cl2 dipole-dipole (DD) partial charge polar covalent a little higher than LD gas or liquid NO CF Hydrogen bonding strongest extreme polar covalent higher than dipole usually liquid HO HN Ionic - much stronger (not really intermolecular, but emphasizes importance of charge) full charges on ions ionic much higher, ionic are solids solid NaCl K2O