The equilibrium constant at $\pu{227 °C}$ for the equation

$$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$

is $K_p = \pu{4.50E3 bar}.$ Calculate the value of $Δ_\mathrm{rxn}G^\circ$ at $\pu{227 °C}$.

With the temperature at $\pu{227 °C}$ and the partial pressures of the gases of $p(\ce{PCl3}) = \pu{0.286 bar},$ $p(\ce{Cl2}) = \pu{0.713 bar},$ and $p(\ce{PCl5}) = \pu{3.06E-6 bar},$ calculate the value of $Δ_\mathrm{rxn}G.$

I calculated $Δ_\mathrm{rxn}G^\circ$ to be $\pu{-34.97 kJ mol-1}.$ Wouldn't it just be

$$Δ_\mathrm{rxn}G^\circ = -\pu{0.0083145 kJ mol-1 K-1} × \pu{500 K} × \ln(\pu{4.5E3})?$$

For the second part of the question I got $\pu{11.20 kJ mol-1},$ but apparently this is also wrong, no doubt because I got the first part wrong.

Would someone care to explain to me?

  • $\begingroup$ What makes you think the first answer is wrong? $\endgroup$ – andselisk Oct 20 '19 at 5:06
  • $\begingroup$ The website we submit the answer to (Sapling) claims it is wrong. $\endgroup$ – Denise Oct 20 '19 at 15:42
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    $\begingroup$ It's like a HW platform. I've tried different sig figs and units are already provided. They don't provide an answer unless you either solve it correctly or press "Give Up". $\endgroup$ – Denise Oct 20 '19 at 16:10
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    $\begingroup$ So I ended up pressing "Give Up". Apparently it wanted only 1 Sig Fig, but no where in the question did it ask for it. $\endgroup$ – Denise Oct 20 '19 at 18:47
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    $\begingroup$ Thank you!!!! :) $\endgroup$ – Denise Oct 20 '19 at 20:43

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