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The equation
CaCO3  CaO + CO2

Gives the decomposition of CaCO3 during heat.
We know that ,  :delta:G=  :delta:H-T :delta:S
However, my book claims that if  :delta:G= 0 i.e., at equlibrium.
This means that the Vapour pressure of CO2 is 1atm if surrounding is 1 atm.  -----------1
How about for solution, what will happen if  :delta:G= 0?-------------------------------2
Concentration = 1 mol dm ^-3???


Please give me some advice on both.
Cheers