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# 10.2 - First law of Thermodynamics and PV graphs

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### Transcript

• 1. Pressure Law Pressure and Temperature aredirectly proportional as long as the temperature ismeasured in Kelvins
• 2. Boyle&#x2019;s LawEach line represents an experiment done at adifferent temperature
• 3. Pistons Wd = P.A.&#x394;d Wd = P. &#x394;V
• 4. Wd = P. &#x394;VAs long as there is an AREA under the line thenyou can see that work is done (and calculate it)
• 5. First Law of ThermodynamicsIt just says that if you add Heat to a gas it must beequal to the Work Done by the gas + any change inInternal Energy This is mainly difficult because: 1. Heat can be gained or lost 2. Internal Energy can rise or fall 3. Work can be done &#x2018;on the gas&#x2019; or &#x2018;by the gas&#x2019;
• 6. 1. Isobaric Constant Pressure1. The gas is expanding &#x2013; doing Work (Work is +ve)2. The temperature is increasing so &#x394;U is increasing (&#x394;U is +ve)3. &#x394;Q = &#x394;U + W so Q must be +ve4. Heat must have been added
• 7. 2. Isovolumetric / Isochoric Constant Volume1. The gas isn&#x2019;t expanding or contracting. No Work is done. &#x394;W=02. Because the Pressure is increasing the temperature must be rising so &#x394;U is +ve3. Q = &#x394;U + W so Q = &#x394;U so heat is +ve4. Heat must have been added
• 8. 3. Isothermic Constant Temperature1. The gas is expanding &#x2013; doing Work (Work is +ve)2. The temperature is constant so &#x394;U is 03. Q = &#x394;U + W so Q =W4. Heat must have been added to enable the gas to do work
• 9. 4. AdiabaticNo Heat is being exchanged &#x2013; perfectly insulated.1. No heat is exchanged so Q = 02. Volume is reducing so Work is being done ON THE GAS (W= -ve)3. Q = &#x394;U + W so 0 = &#x394;U - W4. &#x394;U = W so work done on the gas increases the Internal energy of the gas Adiabatic lines are always steeper than Isotherms
• 10. A Heat Cycle A-B Isochoric / Isovolumetric Temperature rise B-C Isobaric Expansion C-D Isochoric / Isovolumetric Temperature drop D-A Isobaric Contraction
• 11. The Carnot Cycle
• 12. Forward Carnot Cycle
• 13. Reverse Carnot Cycle D