8987754
Description
Flashcards by Lauren Pollock, updated more than 1 year ago
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Created by Lauren Pollock
over 8 years ago
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| Question | Answer |
| First Order Phase Transition | The Gibbs potential is continuous from one phase to another but in a first order phase transition, the first derivatives of the Gibbs potential are discontinuous. This discontinuity originates from the difference in density and specific entropy between the two phases. |
| Second Order Phase Transition | The first derivative of the Gibbs potential is continuous but the second derivative is discontinuous. |
| Vapour Pressure | The pressure at which gas and liquid coexist at thermal equilibrium during the transition region |
| Latent Heat | The energy released or absorbed during a constant temperature process. The heat released during a phase transition is due to the differing entropies of coexisting phases. When a unit amount of phase 1 is converted into phase 2, an amount of latent heat is liberated: l = T_0(s_2-s_1) |
| Critical Point | The point at which gas and liquid have equal density and specific entropy. Phase transition becomes 2nd order. |
| Triple Point | The line along which the gas, liquid and solid can all coexist projects onto the triple point in the PT diagram. The temperature at which all 3 phases can coexist in equilibrium. |
| Critical Isotherm | A constant temperature line on the PT diagram which has an inflection point at the critical point. |
| Clayperon Equation | (∂Δg/∂T)_P * (∂T/∂P)_Δg * (∂P/∂Δg)_T = -1 In equilibrium Δg = 0 dP/dt = l/(TΔV) |
| Intermolecular Potential Energy | Dependent on the magnitude of the intermolecular forces and the position the molecules have relative to each other at any instant of time. 1. Repulsive core - due to the electrostatic repulsion between electron clouds 2. Attractive tail - due to the mutual electrostatic polarisation |
| Van der Waals Equation of State | 1. Hard core replusion leads to V_eff = V-b 2. Reduction due to attraction of neighbouring molecules P =Pkinetic - a/V^2 (V - b)(P + a/V^2) = RT |
| Virial Expansion | Expresses the pressure of a many particle system in equilibrium as a power series in the number density. PV/RT = 1 + 1/V(b - a/RT) |
| Van der Waals Isotherms | At T=T_c, the roots merge. At T<T_c 3 real roots. At T>T_c, one real root and one complex conjugate pair. |
| Isothermal Compressibility | Describes the behaviour of a solid or liquid when the external pressure is changed β_T = -1/V (∂V/∂P)_T |
| Metastable | The stability of a dynamical system in a configuration other than the systems state of least energy (all state defining parameters reach and maintain stationary values). Positive compressibility = Metastable Negative compressibility = Unstable |
| Cavitation | Formation of vapour cavities in a liquid (bubbles). |
| Spinodal Decomposition | Mechanism for the rapid separation of 2 phases into two coexisting phases - it is local and spontaneous |
| Nucleation | A physical process in which the change of state occurs around certain focal points known as nuclei |
| Condition for phase coexistence | In a 1st order transition, coexisting phases have the same P and T. Therefore the condition for equilibrium is therefore that the total Gibbs potential be minimum. G = g_1m_1 + g_2m+2 Condition for phase coexistence: Δg = g_1 - g_2 = 0 - i.e. coexisting phases must have equal chemical potential. |
| Maxwell Construction | VdW isotherm is a monotomic function of V for T>T_c. Below T_c, kink displaying negative compressibility - due to assumption density is uniform. 1st order transition actually involves break up in a mix of phase derivatives. |
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