08_thermodynamicsII_s11

08_thermodynamicsII_s11 - Page 3 Thermal Equilibrium A Q B...

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Thermal Equilibrium if Q=0 then we are in “thermal equilibrium” T A = T B A B Q
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Heat Transfer Three methods Conduction •Transfer Of Energy Through Matter •Air Is A Poor Conductor - Metal is a good one •Only important at the earth's surface Convection •Transfer of energy by movement of mass •Can only take place in liquids & gases - e.g. Air •Convection on a global scale creates worldwide atmospheric circulation Radiation Proportional to the 4th power of the temperature How we get energy from the sun Why it gets cold on a clear night
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The First Law of Thermodynamics – Energy Conservation Many statements: - Energy is conserved - Heat is a form of energy - The energy of an isolated system (e.g. the universe) is constant - Energy is conserved during any change in state. Speci±cally: - Heat absorbed by a system + work done on the system = change in internal energy of the system Mathematically: Δ Q+W= Δ U Q is heat, W is work and U is internal energy
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Latent Heat Latent heat of fusion - Take 1kg of ice at -10 o C and add heat at a rate of 1kcal/min - The Ice will warm up at 2 o C/min - (why 2)? - Once it hits 0 o C - (after 5 min) the ice will start to melt - It will take 80 minutes to melt the ice - So the latent heat of fusion of ice is 80kcal/kg
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Does the 1st law prohibit a lake from freezing on a warm day? 1. Yes 2. No 3. Doesn’t apply
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The 2nd Law of Thermodynamics Many formulations: - It is impossible to convert heat completely into work. -
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08_thermodynamicsII_s11 - Page 3 Thermal Equilibrium A Q B...

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