What determines phase of matter? Measured by temperature – a measure of the average kinetic energy of a group of particles. 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. A.K.A. “Van der Waals forces” Attraction between oppositely charged ends of different polar particles H is bonded to N, O, or F
How do substances change state? Beginning StateEnding StateProcess of Change SolidLiquidMelting SolidGasSubliming LiquidSolidFreezing LiquidGasEvaporating/Boiling Gas Solid LiquidCondensing Deposition
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? Boiling point is directly related to atmospheric pressure, and indirectly related to altitude! LocationAltitude (ft)PressureBoiling Point Sea Level0760 mmHg100 ºC (373 K) Mt. Everest29,028240 mmHg70 ºC (343 K)
Boiling vs. Evaporation Occurs below the boiling point, only at the surface of the liquid. Occurs at the boiling point, throughout the entire liquid. Heat of vaporization: the amount of heat required to vaporize a liquid. Normal Boiling Point: the temperature at which vapor pressure of a liquid is equal to atmospheric pressure.
Line D represents water. If the atmospheric pressure in a flask is lowered to 70 kPa, water would boil at what temperature?
Freezing and Melting Points At what temperature does water freeze? At what temperature does ice melt? (Freezing point) (Melting point) Heat of Fusion: the amount of heat required to melt a solid to liquid
Particles are Always in Motion GASES 1.Gases are composed of tiny particles 2.Particles are in constant motion 3.Elastic collisions occur between particles 4.There are no attractive forces between particles 5.Kinetic Energy increases when temperature increases.
Particles are Always in Motion LIQUIDS 1.Viscosity: the friction or resistance to motion that exists between the molecules of a liquid 2.Surface Tension: the imbalance of forces at the surface of a liquid
Particles are Always in Motion SOLIDS 1.Particles are “locked” in position and can only vibrate 2.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
Thermodynamics Enthalpy (H): how much heat is in a system. Used to determine whether a reaction is endothermic or exothermic. Entropy (S): how much is in the system D I S OR D E R Gibb’s Free Energy (G): is the reaction spontaneous?
How do we use Enthalpy? For any given reaction, heat is either used or given off. ENDOTHERMICEXOTHERMIC We can use enthalpy to calculate heat transfer H: the amount of heat it takes to form a certain substance. This information can be found on the chart of standard enthalpies. H total = H products - H reactants
Reaction Coordinates EXOTHERMICENDOTHERMIC R P = EXP R = EN
Let’s see how Enthalpy works: 2 H 2 (g) + O 2 (g)2 H 2 O (l) H total = H products - H reactants H total = 2 mol(-285.83 kJ/mol) - H total = -571.66 kJ [2 mol (0 kJ/mol) + 1 mol (0 kJ/mol)]
Practice with Enthalpy Calculate H for the following reactions: 2 KBr (s) + I 2 (g)2 KI (s) + Br 2 (g) 2 HCl (g) + 2 Ag2 AgCl (s) + H 2 (g) H total = [2mol (-327.9 kJ/mol) + 1mol (0 kJ/mol)] - [2mol (-393.8 kJ/mol) + 1mol (0 kJ/mol)] H total = 131.8 kJ H total = [2mol (-127.01 kJ/mol) + 1mol (0 kJ/mol)] - [2mol (- 92.31kJ/mol) + 2mol (0 kJ/mol)] H total = -69.40 kJ ENDOTHERMIC EXOTHERMIC
Entropy and Gibb’s Free Energy They work the same way!! “PRODUCTS – REACTANTS” S total = S products - S reactants G total = G products - G reactants S > 0, entropy increases (more disorder) S < 0, entropy decreases (less disorder) G > 0, not spontaneous G < 0, spontaneous G = 0, equilibrium
How do H, S, and G Relate? G = H - T S Potassium bromide reacts with iodine at 345K. Will this reaction occur spontaneously? 2 KBr (s) + I 2 (g)2 KI (s) + Br 2 (g) H total = [2mol (-327.9 kJ/mol) + 1mol (0 kJ/mol)] - [2mol (-393.8 kJ/mol) + 1mol (0 kJ/mol)] H total = 131.8 kJ S total = [2mol (106.3 J/mol K) + 1mol (152.21 J/mol K)] - [2mol(95.9 J/mol K) + 1mol (116.14 J/mol K)] S total = 56.87 J/ K
How do H, S, and G Relate? G = H - T S Potassium bromide reacts with iodine at 345K. Will this reaction occur spontaneously? 2 KBr (s) + I 2 (g)2 KI (s) + Br 2 (g) H total = 131.8 kJ S total = 56.87 J/ K G = 131,800 J – (345K)(56.87 J/K) = 131,800 J G = 131800 J – 112179.85 J G = 19620.15 J 19600 J = 19.6 kJ
For Next Class: Complete homework page of packet.