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Thermo%202%202009(2)

Thermo%202%202009(2) - Mat E 510 Thermodynamics of Solids...

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Mat E 510 Thermodynamics of Solids Mat E 510 Thermodynamics of Solids Based on Prof. Roger Doherty’s course Lecture #2 Yury Gogotsi A.J. Drexel Nanotechnology Institute and Department of Materials Science & Engineering, Drexel University, Phil d l hi P l i USA Philadelphia, Pennsylvania, USA
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f Endothermic Definitions Exothermic Macroscopic state of the system Standard State Equation of state Enthalpy Enthalpy of fusion Enthalpy of vaporization Entropy
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First Law of Thermodynamics This is extension of the law of conservation of energy. Conservation of energy U Newton's Third Law Conservation of energy, - Newton s Third Law. Equal and opposite forces. Work done by the body: d w = f d l f – force, l - distance Also conservation of momentum d m ' = f d t . Potential Energy to Kinetic Energy: (Newton’s laws) work w = force x distance = mgh = mv 2 /2 Mechanical equivalent of heat. 4 154 J (Newton meter) = 1 Calorie 4.154 J (Newton-meter) 0.239 cal per joule – thermochemical calorie (rounded from 0.2389) 1 calorie (or 15º calorie) the heat to raise the temperature of 1 g of water from 14.5 to 15.5 °C Specific Heat, C p , of water is 4.154 J/g 4.154 kJ/kg (at P = 1 atm). Originally 1 cal/g. Work transforms to heat by viscosity or friction.
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Temperature and Energy Two ways of raising "temperature": By heat (drop in a heated copper ball - copper at higher temperature") or b mechanical ork Both raise the energ of the material or by mechanical work. Both raise the energy of the material. Heat – Energy flow by virtue of difference in “temperature” Work – Energy flow capable of raising a weight For infinitesimal change of state: d U = δ q - δ w Performance of the work decreases U Absorption of heat increases U This defines a change of internal energy, U q positive – endothermic process, heat flows out of a body q negative – exothermic process heat flows into a body negative exothermic process, heat flows into a body q zero – adiabatic process
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The First law (Conservation of Energy) We define Internal Energy, U , by: d U = δ q - δ w Can we measure the absolute value of the Internal Energy? How is it stored? Specific heat - increased atomic vibration M ki b ki f i b d Making or breaking of atomic bonds Latent heat Chemical Reaction Heat - breaking and remaking chemical bonds 2Mg + O 2 -> 2 MgO > 2 MgO Statement of First Law: Internal Energy is a State Function : U = f ( T , P ,…) The same amount of work, however it is performed (motion, electrical current, friction, etc.) brings about the same change of the system (means, change of state is path independent)
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Other Statements of the First Law Equivalent statements: The change Δ U AB Δ U AB = U B - U A = q - w is path independent . In the case of a cyclic process which returns the system to its initial state, the change of U is zero B A or cyclic integral Δ U = d U + d U = (U U ) + (U U ) = 0 B -U A ) + (U A -U B ) = 0 A B Or: Energy is conserved .
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