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I have read in my notes that seeing the slope of a process in a PV diagram and comparing it with the isothermal slope, we can predict that is the temperature increasing or decreasing at that point. But i haven't mentioned the reason or the result for that. Since i had taken up thermodynamics a long time ago i don't remember any explanation for this. Can anyone please help me confirm if this is true or not?

Also isothermal slope at that point be taken as P/V (just to clarify).

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Going from $A$ to $B$ the temperature is increasing.
You can compare the gradients and see that a less negative gradient than that of the isotherm will result in a higher temperature.

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  • $\begingroup$ Thank you very much. I don't know why i did not think that. $\endgroup$ – Nisarg joshi Nov 20 '16 at 11:11
  • $\begingroup$ Also is there a similar relation for heat( increasing or decresing) with the adiabatic slope at a point? $\endgroup$ – Nisarg joshi Nov 20 '16 at 11:12
  • $\begingroup$ Heat does not increase or decrease as it is either heat entering a system or heat leaving a system. The first law tells you that you can change the internal energy of a system by either doing work on a system or supplying heat to a system. $\endgroup$ – Farcher Nov 20 '16 at 12:40
  • $\begingroup$ Sorry i meant , is it possible to know if the heat is being absorbed or released by comparing the slope of graph with adiabatic slope at that point. $\endgroup$ – Nisarg joshi Nov 20 '16 at 12:45
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(P, V1) be any point in the first curve with T1; (P, V2) be the point in the next curve with T2; The process is isothermal; PV1=mRT1; PV2=mRT2; P(V2-V1) = mR(T2-T1). (actually it is an isobaric curve); if T2 is higher than T1 the Rhs is to be positive This implies the LHS is positive.ie V2-V1 is positive, V2>V1. hence The second curve is above the first one.

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