Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Mimic on June 01, 2019, 03:32:30 PM
-
For the reaction
[tex]\ce{CO2 (g) + H2 = CO (g) + H2O (g)}[/tex]
he equilibrium constant [itex]K_p[/itex] has a value of 0.534 at [itex]{960 K}[/itex] and [itex]{1.571 K}[/itex]. Calculate the variation of the standard reaction enthalpy, assumed constant in the temperature range considered. Also calculate the [itex]K_p[/itex] value of the above reaction at standard conditions at [itex]{25 ^\circ C}[/itex].
My procedure:
[tex]K_c = K_p(RT)^{\Delta \nu (g)} = K_p(RT)^{0} = K_p \cdot 1 = K_P[/tex]
from the van't Hoff equation
[tex]\ln K_2 - \ln K_1 = - \dfrac{\Delta H^{°}_{r}}{R} \left[\dfrac{1}{T_2} - \dfrac{1}{T_1}\right][/tex]
[tex]\Delta H^{°}_{r} = + 36.177 \dfrac{kJ}{mol}[/tex]
Now, for [itex]K_p[/itex] at [itex]{25 ^\circ C}[/itex]
[tex]K_p = \exp^{-\dfrac{\Delta G^{°}_{r}}{RT}}[/tex]
which of the two equations should I use to calculate [itex]\Delta G^{°}_{r}[/itex]?
[tex]\Delta G^{°}_{r} = \Delta H^{°}_{r} - T\Delta S^{°}_{r}[/tex]
or
[tex]\Delta G^{°}_{r} = \sum_{products} \nu \Delta G^{°}_{f} - \sum_{reagents} \nu \Delta G^{°}_{f}[/tex]
Can you help me?
Thank you in advance
-
What do you mean by
Kp has a value of 0.534 at 960K and 1.571K.
Do you mean a value of 0.534 at 960K and a value of 1.571 at some other temperature?
which of the two equations should I use to calculate ΔGr°?
Well, which do you have the information for?
Note that this is not as simple as it may appear (though, as a homework question, they may be expecting you to use the over-simplified approach). Over this range of temperature (950 to 298K), ΔH and ΔS will not be constant. Also, the standard state of water at 298K is liquid, not gas.