C+ 2CO. 4.5 The equilibrium constant for the reaction H2 + I2 = 2HI is 45.6 at 7
ID: 1036275 • Letter: C
Question
C+ 2CO. 4.5 The equilibrium constant for the reaction H2 + I2 = 2HI is 45.6 at 764 K and 60.8 at 667 K. Estimate the enthalpy change which accom- panies 1 mole of the forward reaction. 4.6. The enthalpy of vaporization of water at 373 K and 1 bar is 40.7 kJ mol-1. Estimate the vapour pressure of water at 368 K. 4.7. In the Handbook of Chemistry and Physics the following data are given for the vapour pressure of mercury Temp/°C 0 4 Pressure/mmHg 0.000185 0.000276 0.000406 0.000588 Calculate the entropy and enthalpy changes accompanying vaporiza- tion at 1 bar and the Gibbs energy change accompanying vaporization at 273 K and at the boiling point of mercury. 12Explanation / Answer
4.5) From Van 't Hoff equation
ln(K2/K1) = -?Ho/R (1/T2 - 1/T1)
ln(60.8/45.6) = -(?Ho/8.314) x (1/667 - 1/764)
0.288 = -(?Ho/8.314) x (1.90 x 10-4)
Therefore ?Ho = -12579.11 kJ/mol
4.6) The Clausius- Clapeyron equation. If P1 and P2 are the pressures at two temperatures T1 and T2, the equation has the form:
ln(P1/P2) = ?Hvap/R (1/T2 - 1/T1)
P1 = 1bar = 0.99 atm T1 = 373k
P2 = ? atm T2 = 368k
?Hvap = 40.7 kJ/mol = 40700 J/mol
ln(0.99/P2) = 40700/8.314 (1/368 - 1/373)
ln(0.99/P2) = 0.178
0.99/P2 = exp(0.178) = 1.19
Therefore P2 = 0.99/1.19 = 0.83 atm
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