Class Notes (838,375)
Chemistry (614)
CHEM 205 (63)
David Chen (27)
Lecture

# CHEM205 Thermodynamics.rtf

6 Pages
160 Views

Department
Chemistry
Course
CHEM 205
Professor
David Chen
Semester
Winter

Description
THERMODYNAMICS Laws of Thermodynamics: 0th Law: absolute temperature (0K = no movement/vibrations) 1st Law: conservation of energy - keeping track of energy changes and allow us to calculate the heat a reaction produces 2nd Law: why some rxns occur but others don’t by keeping track of changes of both enthalpy and entropy (system and surroundings) 3rd Law: defines absolute entropy for a pure substance Ideal Gas (IG): PV = nRT Combined Gas Law: P V /1 1 P1V /T2 2 2 Dalton’s Law of Partial Pressure: P(total) = P1 + P2 + P3... Kinetic Model of Gas: - continuous/random motion - infinitesimally small points - move in straight lines until collision - do not interact each other except for collisions (i.e. no repulsive/attractive forces) E(kinetic) = ΔU = (f/2)RT where f is the degrees of freedom; 3 for monoatomic, 5 for diatomic Degrees of freedom are based on translational and rotational Van der Waals Equation: (P+an^2/V^2)(V-nb) = nRT 1. Repulsive interaction (Size effect): IG are assumed to have no volume but in reality gases take up some amount of volume. So, V is replaced by V - nb, where b is the volume/mole occupied by the gas. 2. Attractive forces: Molecules spend more time with each other during a collision and as a result, they collide less with the wall. Compressibility factor: Real Gas: z = pV/nRT Ideal Gas: z = 1 Virial Equation of State: z = PV/nRT = 1 + B2p*P + B3p*P + … where B2p, B3p... are Virial coefficients Terminology: - Irreversible: System =/= Surroundings - Reversible: System = Surroundings Thermodynamic Processes: - Isothermal: T = constant - Isobaric: P = constant - Isochoric: V = constant - Adiabatic: q = 0 (no heat enters/leaves) - Exothermic: q < 0 - Endothermic: q > 0 Properties: - System - part of universe we’re interested in - Surrounding - rest of universe - Open: allows exchange of matter and energy - Closed: allows exchange of energy - Isolated: does not allow exchange of matter or energy - State function: A => B depends only initial and final state; independent of path - Extensive: proportional amount of materials (i.e. m, V, E) - Intensive: depends on nature of materials (i.e. density, T, P) The First Law of Thermodynamics: Conservation of energy 1. Heat Transfer 2. Work Closed system: ΔU = UB - UA = q + w q - heat supplied TO the system w - work done ON the system Reversible and Irreversible Isothermal Expansions: Reversible: follows PV=nRT graph What is reversible? 1. IG Expansion/Compression: P = nRT/V 2. Heating/Cooling a stable substance 3. Chemical reaction at equilibrium 4. Phase transition along phase boundary Work: Irreverisible/constant external pressure: w = -PexΔV Reversible (Pex = P): dw = -PexdV => w = -nRT ln (V2/V1) Vacuum (Pex = 0): w = 0 ΔV = 0: w = 0, ΔU = Δqv Enthalpy H≡U + PV Isobaric: ΔH = qp Calorimetry: Measurement of Heat Heat Capacity C - the energy required to increase the temperature by 1o q = CΔT C≡q/ΔT (J K-1) ΔU = ∫ n*Cv,m dT = 3/2nRΔT Isobaric: Cp = n*Cp,m = (dq/dT)p ΔH = ∫ n*Cp,m dT = 5/2nRΔT Relationship between Cp and Cv: Cp - Cv = nR **Molar heat capacity does not exist for mixtures The Second Law of Thermodynamics - the entropy of an isolated system increases in the course of any spontaneous change - Spontaneous change - a change happens naturally without being driven by an external force - Nonspontaneous change - a change with no natural tendency Entropy: Entropy S - a measure of disorder Influenced by... - Thermal disorder - increase T = increase thermal motion - Positional disorder - spread into greater volume/mixing Reversible: dS = dq /Trev ΔS = ∫dq /T OR ΔSrevC ln (T /T ) 2 1 Irreversible: make hypothetical reversible path Isothermal: ΔS = q /Trev-w /T =revln (V /V ) O2 Δ1 = nRln (P /P ) 1 2 Isochoric: dq rev= n*CvdT = dU => ΔS = n*Cv ln (T /T ) 2 1 Isobaric: ΔS = n*Cp ln (T /2 )1 Adiabatic: ΔS = 0 Phase Chan
More Less

Related notes for CHEM 205
Me

OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Join to view

OR

By registering, I agree to the Terms and Privacy Policies
Just a few more details

So we can recommend you notes for your school.

Get notes from the top students in your class.

Request Course
Submit