Latest post: 18/04/2005, 9:23 p.m.

Hello all, I block a small question over a range of temperature which we interesson, changes in the saturation vapor pressure of p1 * Tolunę with the temperature steam viscosity T can be reprsentes realtion by: ln (P1 *) = 11.93- (4544 / T) => Can considrer the molar vaporization enthalpy of Tolunę is constant over the range of temperature considr ? If so, how determine its value? thank you in advance for your help
Join Date October 2009
I would tend to say that we must look at the critical point, and so far it is a must be good. (You have to remember that this phase change enthalpy becomes zero at the critical point).
Formula is used Clapeyron: Lv = T (Vv - V liq) dP / dt avev Vv: molar volume of steam Vliq: molar volume of liquid Approximations: Steam ideal gas Vv = RT / PV liq = 0 Lv = T * RT / P * dP / dT is Lv = RT ^ 2 * dLnP / dT .... we almost finished ...
Well as I have the solution today (and yes prof is not nerv) I give you a. We start with a balanced liquid steam viscosity (L) - Steam (G) So we can write L = G constant steam viscosity of this equilibrium is K = a (G) / a (L) (as has the activity ) The activity of the liquid is 1 (assuming pure liquid) and that of the vapor is: P / P the pressure P is actually Psat the saturated vapor pressure. d (LNK) / dT = (Delta (r) H) / (RT) here was a spray so our Delta (r) will be a Delta H (vap) H. It rearranges the words in d (LNK) = (Delta (vap) H.dT) / (RT) We must now integrate. For this it is necessary to know the limits. We must therefore take terminals that allow a simplification of the expression. For intgrale d (LNK) will be taken between 1 and Psat and dT / T on and T take between Teb. Let me explain! The temperature of boiling pressure must be connected (we know that the water does not boil at the same temperature of the mother and it comes from the altitude diff ence in pressure between steam viscosity the two places.). steam viscosity It was therefore the temperature of boiling worth Teb when one is P. If we refer in K = a (G) / a (L) = P / P are obtained for K = 1 P = P. Voil for the explanation of the First Point. The SECOND in dcoule: a temperature T will combines Psat saturation vapor pressure. By integrating, we obtain: LNPS = [(1 / T b) - (1 / T)]. Delta (vap) H / R We dduit the coefficient "above T" (ln (p1 *) = 11.93- (4544 / T)) is saying 4544 is Delta (vap) H / R (just dvelopper steam viscosity and identify Member member). D'o Delta (vap) H = 4544.R = 37.7 kJ / mol Voil for that matter. I guess the rest of the year intressera others so do not hesitate. Sincerely Coulonval
just for those who have seen the Clapeyron formula can end the year: dlnp / dt = 4544 / T ^ 2 so Lv = RT ^ 2 dlnp / dt = R * 4544 J / mol but the solution proposed is also applies, of course!
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Latest post: 18/04/2005, 9:23 p.m.