Chemistry

Consider the following reaction:
CaCO3(s)→CaO(s)+CO2(g).
Estimate ΔG∘ for this reaction at each of the following temperatures. (Assume that ΔH∘ and ΔS∘ do not change too much within the given temperature range.)

for 310K,1070,1470

this is what i did
dH (kJ/mol)dS (J/moleK)
CO2(g) (-393.51) (213.6)
CaCO3(s) (-1206.9)(92.9)
CaO(s) (-635.1)(39.8)

CO2(g) +CaO(s) -CaCO3(s)
dH = -393.51 + (-635.1) - (-1206.9) = 178.29
dS = 213.6 + (39.8) - (92.9) = 160.5

dG = dH - TdS =
dG = 178.29 - 310 x 0.1605 = 130
dG = 178.29 - 1070 x 0.1605 = 6.55
dG = 178.29 - 1470 x 0.1605 = -57.65

However only 310 is correct i don't know what i am doing wrong for the other two

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asked by Ty
  1. I don't know. I looked up the numbers in my text. Although they are slightly different I obtained essentially the same values you did; i.e., 128.2, 6.05, and -58.2 all in kJ/mol.
    I also looked up dGo in the same text and it was 130.4 at T = 298 and using
    dG = dH - TdS I obtained 130.1 which tells me the formula is ok.
    In previous instances like this, where it seems everything is ok but the data base says you're wrong, it has been a case of significant figures (too many or too few). I suggest you look at that closely.

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