Phases of Matter & Thermodynamics

Line D represents water. If the atmospheric pressure in a flask is lowered to 70 kPa, water would boil at what temperature?

Phases of Matter & Thermodynamics Ms. Besal 3/23/2006

What are the States of Matter? Gases Liquids Plasma Solids

Gases How can we define E X P A N D A B L E Diffusible... Low Density L E T T I S O ! O D D R A R

Liquids How can we define Close together Definite Volume No Definite Shape R D S E S M I E O D R O

Solids How can we define VERY Close together Definite Shape Definite Volume O R D E R !

What determines phase of matter? Measured by temperature – a measure of the average kinetic energy of a group of particles. HEAT Intermolecular Forces The attraction between molecules; increases as the amount of heat in a system decreases.

What types of Intermolecular Forces are there? Creates a temporary polar area in the particle which is attracted to temporary polar areas in other particles. Dispersion Forces A.K.A. “Van der Waals forces” Attraction between oppositely charged ends of different polar particles Dipole-Dipole Hydrogen Bonding H is bonded to N, O, or F

Beginning State Ending State Process of Change How do substances change state? Solid Liquid Melting Solid Gas Subliming Liquid Solid Freezing Liquid Gas Evaporating/Boiling Gas Solid Deposition Gas Liquid Condensing

Location Altitude (ft) Pressure Boiling Point Boiling Points • The temperature at which a substance turns from liquid to vapor • Thought question: • Is the boiling point of a liquid the same in every location? NO! Boiling point is directly related to atmospheric pressure, and indirectly related to altitude! Sea Level 0 760 mmHg 100 ºC (373 K) Mt. Everest 29,028 240 mmHg 70 ºC (343 K)

Boiling vs. Evaporation Evaporation Occurs below the boiling point, only at the surface of the liquid. Occurs at the boiling point, throughout the entire liquid. Boiling Normal Boiling Point: the temperature at which vapor pressure of a liquid is equal to atmospheric pressure. Heat of vaporization: the amount of heat required to vaporize a liquid.

Line D represents water. If the atmospheric pressure in a flask is lowered to 70 kPa, water would boil at what temperature? 92ºC

Freezing and Melting Points At what temperature does water freeze? SAME! 0 ºC (Freezing point) At what temperature does ice melt? 0 ºC (Melting point) Heat of Fusion: the amount of heat required to melt a solid to liquid

Particles are Always in Motion Kinetic-Molecular Theory GASES • Gases are composed of tiny particles • Particles are in constant motion • Elastic collisions occur between particles • There are no attractive forces between particles • Kinetic Energy increases when temperature increases. Ideal Gases!

Particles are Always in Motion Kinetic-Molecular Theory LIQUIDS • Viscosity: the friction or resistance to motion that exists between the molecules of a liquid • Surface Tension: the imbalance of forces at the surface of a liquid

Particles are Always in Motion Kinetic-Molecular Theory SOLIDS • Particles are “locked” in position and can only vibrate • Can be classified by three main characteristics: • Hardness • Electrical Conductivity • Melting Point

How do we classify solids? • Crystalline Solids: • organized, definite, repetitive, sharp melting point • metallic: conduct electricity well • molecular: soft, low melting point • ionic: hard, brittle • covalent-network: conduct electricity at high temperatures • Amorphous Solids: • not “true” solids because molecules do move some • high viscosities make them appear solid • they soften before melting

I D O R E Entropy (S): how much is in the system R D S Thermodynamics Enthalpy (H): how much heat is in a system. Used to determine whether a reaction is endothermic or exothermic. kJ J/K Gibb’s Free Energy (G): is the reaction spontaneous? kJ

How do we use Enthalpy? For any given reaction, heat is either used or given off. ENDOTHERMIC EXOTHERMIC We can use enthalpy to calculate heat transfer DH: the amount of heat it takes to form a certain substance. This information can be found on the chart of standard enthalpies. DHtotal = DHproducts - DHreactants

Reaction Coordinates EXOTHERMIC ENDOTHERMIC R EX P EN = = P R

Let’s see how Enthalpy works: 2 H2 (g) + O2 (g) 2 H2O (l) DHtotal = DHproducts - DHreactants DHtotal = 2 mol(-285.83 kJ/mol) - [2 mol (0 kJ/mol) + 1 mol (0 kJ/mol)] DHtotal = -571.66 kJ

Practice with Enthalpy Calculate DH for the following reactions: 2 KBr (s) + I2 (g) 2 KI (s) + Br2 (g) DHtotal = [2mol (-327.9 kJ/mol) + 1mol (0 kJ/mol)] - [2mol (-393.8 kJ/mol) + 1mol (0 kJ/mol)] DHtotal = 131.8 kJ ENDOTHERMIC 2 HCl (g) + 2 Ag 2 AgCl (s) + H2 (g) DHtotal = [2mol (-127.01 kJ/mol) + 1mol (0 kJ/mol)] - [2mol (- 92.31kJ/mol) + 2mol (0 kJ/mol)] DHtotal = -69.40 kJ EXOTHERMIC

Entropy and Gibb’s Free Energy They work the same way!! “PRODUCTS – REACTANTS” DStotal = DSproducts - DSreactants DS > 0, entropy increases (more disorder) DS < 0, entropy decreases (less disorder) DGtotal = DGproducts - DGreactants DG > 0, not spontaneous DG < 0, spontaneous DG = 0, equilibrium

How do H, S, and G Relate? DG = DH - TDS Potassium bromide reacts with iodine at 345K. Will this reaction occur spontaneously? 2 KBr (s) + I2 (g) 2 KI (s) + Br2 (g) DHtotal = [2mol (-327.9 kJ/mol) + 1mol (0 kJ/mol)] - [2mol (-393.8 kJ/mol) + 1mol (0 kJ/mol)] DHtotal = 131.8 kJ [2mol (106.3 J/mol K) + 1mol (152.21 J/mol K)] - DStotal = [2mol(95.9 J/mol K) + 1mol (116.14 J/mol K)] DStotal = 56.87 J/ K

How do H, S, and G Relate? DG = DH - TDS Potassium bromide reacts with iodine at 345K. Will this reaction occur spontaneously? 2 KBr (s) + I2 (g) 2 KI (s) + Br2 (g) DHtotal = 131.8 kJ = 131,800 J DStotal = 56.87 J/ K DG = 131,800 J – (345K)(56.87 J/K) DG = 131800 J – 112179.85 J DG = 19620.15 J  19600 J = 19.6 kJ

For Next Class: • Complete homework page of packet.

Phases of Matter & Thermodynamics