m-xylene (MXY) has an atmospheric boiling point of 410 K. Calculate the vapour p

Question

m-xylene (MXY) has an atmospheric boiling point of 410 K. Calculate the vapour pressure of m-xylene at 300K. Assume that delta H_vap is independent of temperature. Delta H degree_t(MXY_y I) = -24.0 kJ/mol, delta H degree/t(MXY_g) = +18.0 kJ/mol Calculate the entropy changes, delta S, for the following process. Data: delta H degree_f(H_2O, liq) = -285 kJ/mol; C_p, m(H_2O, liq) = 75 J/K.mol; delta H degree_f(H_2O, gas) = -242 kJ/mol; C_p, m(H_2O, gas) = 34 J/K.mol a) 2.5 mol H_2O(liq) is heated from 20 degree C to 100 degree C. Assume C_p is independent of temperature b) 2.5 mol of H_2O(liq) is evaporated reversibly at its atmospheric boiling point, p = 1 atm, T = 373K

Explanation / Answer

Q3.

first, get Hvap

Hvap = Hgas - Hliquid = 18 - -24 = 42kJ = 42000 J

now

this is at T1 = 300 K P = 1

we need T2 = 410; P2 = ?

so

ln(P2/P1) = dHvap/R*(1/T1-1/T2)

ln(P2/1) = 42000 /8.314*(1/300-1/410)

Solve for P2

P2 = exp(42000 /8.314*(1/300-1/410))

P2 = 91.633 atm

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