I was asked to find delta Grxn for the equation I2+Cl2--->2ICl. Was given information to solve for Q (PICl= 2.55atm, PI2=0.315, PCl2=0.216), i ended up with 4.4588. Then I solved for the standard G rxn by: Delta G= (-10.9*2)- (19.3+0)= -41.1.
I used the equation: delta G=delta G standard rxn + RTlnQ. Temperature was 298K.
I ended up with -152221 kj. However, it said it was wrong. Perhaps my standard free energy for ICl was wrong. Couldn't find it in the text so computed it by using delta G=-RTlnK. K being 81.9.
Somebody please help me find what it is i did wrong. Thank you!!
To determine what went wrong, let's go through the steps one by one:
1. Calculate Q: You correctly calculated the value of Q as 4.4588 using the partial pressures given for PICl, PI2, and PCl2.
2. Calculate standard ΔG for the reaction: You correctly used the equation ΔG = ΔG° + RTlnQ. Given that you know the value of Q and ΔG (ΔG°) = -41.1 kJ, you can rearrange the equation as follows:
-41.1 kJ = ΔG° + (8.314 J/(mol·K) * 298 K) * ln(4.4588)
By plugging in the values, you should obtain ΔG° ≈ -54.46 kJ/mol (remember to convert kJ to J).
3. Calculate ΔG for the reaction: To calculate ΔG, you need to use the equation ΔG = ΔG° + RTlnK, not -RTlnK as you mentioned. Given that the temperature is 298 K and the value of K is 81.9, you can substitute these values into the equation:
ΔG = -54.46 kJ/mol + (8.314 J/(mol·K) * 298 K) * ln(81.9)
By plugging in the values, you should obtain ΔG ≈ -152.18 kJ/mol (again, remember to convert J to kJ).
Based on the calculations, it seems that you made a mistake in the sign while converting J to kJ in step 2. The correct value for ΔG should be approximately -152.18 kJ/mol, not -152,221 kJ/mol.
Please double-check your calculations and make sure to convert the units correctly. Let me know if you need further assistance.
To find the standard free energy change for the reaction, ΔG˚, you need to use the equation:
ΔG˚ = -RTlnK
Where R is the ideal gas constant (8.314 J/mol·K), T is the temperature in Kelvin (298 K in this case), and K is the equilibrium constant.
In your case, you found K to be 81.9. Plugging in these values, you should get:
ΔG˚ = - (8.314 J/mol·K) * (298 K) * ln(81.9)
ΔG˚ ≈ -8.314 * 298 * ln(81.9) ≈ -18887 J/mol
However, it seems that you calculated the value of ΔG using the incorrect sign. The negative sign is necessary to indicate that the reaction is exothermic and that it favors the formation of products. Therefore, the correct value for ΔG˚ should be approximately 18887 J/mol.
Note: The unit for ΔG should be Joules per mol, not kilojoules per mol.