3.020 Lecture 2 1. Scope of thermodynamics (a) states of matter: have well-deﬁned response to – squeezing – heating – adding more stuﬀ – diﬀerent stuﬀ – applying ﬁelds (b) Transformations between states • Starting/ﬁnal states described with certainty e.g. phase diagrams • Process is abstract • Kinetics is not described ⇒ no time in thermo ⇒ Thermo describes the why, only hints at the how. 2. Use of thermodynamics • Predict & Control matter • Transfer Knowledge e.g. phase diagrams 1 3. Systems in thermodynamics • Characterized by : – Temperature – Pressure – Volume – Composition • Draw boundaries out of convenience e.g. adding sugar to a glass of water and stir • System: H2 O Sugar Glass atmosphere stirring stick • Boundaries: open/closed rigid/not rigid adiabatic/diathermal 2 4. Types of systems: Classiﬁcations (I) Uniary=one component e.g. H2 O v.s. e.g. H2 O + C12 H22 O11 MultiComponent (I) Homogeneous = one phase e.g. sodium acetate solu. v.s. Heterogeneous = more than one phase e.g. sodium acetate solu.+solid sodium acetate (I) Closed = no mass exchange with surroundings Open = can exchange mass 5. e.g. closed soda bottle e.g. open soda bottle State functions/variables • Characterize a system • Independent of history Common state functions found in 3.020: 6. • temperature (T) • composition (c.t.%) • pressure (P) • mole # (N) • entropy (S) • Gibbs free energy (G) • volume (V) • etc. Equations of state e.g. P V = N RT PV P a · m3 N · m3 N ·m J R= ∝ = 2 = = NT #·K m ·K K K 3 7. Thermodynamic properties • Compressibility β = − V1 � ∂V � ∂lnV = − ∂P T ∂P T � � • Thermal expanstion α = V1 ∂V = ∂lnV ∂T P ∂T P e.g. Compressing an ideal gas at ﬁxed temperature Vi (Pi ) → Vf (Pf ) 1 ∂ N RT N RT N RT 1 1 β=− = = = 2 V ∂P P VP VP P P T simple for ideal gas Z Pf Vf = Vi + Z 8. N RT N RT + Pf Pi Z Pf dP (−V β) = Vi − dV = Vi + Pi = Vi − Pf Pi dP Pi N RT 1 P P trivial for ideal gas Intensive v.s. extensive properties • Intensive: Can be deﬁned at any point in a system e.g. temperature, density, composition, pressure, compressibility • Extensive: Depends on extent of system, scales with system size e.g. energy, volume, moles, entropy, mass 4 9. Phases of matter • Phase = region of space within which all (intensive) properties are uniform e.g. solid sucrose, pure water, sugar, sugar water, pure copper, pure zinc, brass • Phase boundaries classiﬁed similarly to system boundaries e.g. sugar + sugar water. exchanging volume, heat energy and mass across the phase boundary 5

Lecture 2 Notes: Scope and Use of Thermodynamics

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