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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
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
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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