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Unformatted text preview: FNTs from DL 15 FNT 2) What is the physical basis for the difference in measured values of C p and C v for a gas? The physical reason why C p and C v have different values is that C v is measured when our volume is constant and unchanging, so no work is done on or by the system. Heat capacity is equal to the heat gained or lost by the system, divided by the change in temperature [ C = Q/(change in T) ]. When no work is done, our change in internal energy (delta U) is equal to the heat. When we calculate C p , our system remains at constant pressure but our volume can change. So whenever we add Q (and increase T), our volume changes (PV = nRT), which means work is done ( W = -P *(change in Volume)). In this case, our heat is equal to our change in internal energy minus whatever energy changes are due to work. Using PV = nRT and W = - P*(delta V) and p(delta V) = nR (delta T) , we can find the relationship between C p and C v to be: C p = C v + nR so C p > C v always 3) (I) Q =0 (II) change in internal energy =0 (III) W=0 a)An isochoric (constant volume) process: I I I b/c of Thermodynamic model [W = - P(change in V)] b)An isobaric (constant pressure) process: None of these are necessarily...
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This note was uploaded on 05/12/2010 for the course PHY 7 taught by Professor Staff during the Spring '08 term at UC Davis.
- Spring '08