[Ice-cream]

hey can any1 help me out?

At 900degrees C, Kp = 1.04 for the reaction
CaCO3 (s) --> CaO(s) + CO2(g)
At a low temperature, dryi ice (solid CO2), calcium oxide and calcium carbonate are introduced into a 50L reaction chamber. The temperature is raised to 900dgrees C, resulting in the dry ice converting to gaseous CO2. For the following mixtures, will the initial amount of calcium oxide increase, decrease or remain the same as the system moves toward equilibrium at 900degrees C?
a) 655g CaCO3, 95.0g CaO, P(CO2) = 2.55atm
b) 780g CaCO3, 1.00g CaO, P(CO2) = 1.04atm

I can do the rest (part  c and d) if i know how to do a) or b) so can any1 tell me how i'm meant to approach this question? i really don't know how to start it. for one thing, i realise that only gases would be participating in calculating the pressure equilibrium.

they say the answer is "decreases".

[Borek]

I am not quite sure if I understand the question properly:

655g CaCO3, 95.0g CaO, P(CO2) = 2.55atm

What P(CO2) = 2.55 atm stands for? Is this pressure just after heating, but before equilibrium is reached? If so, that's the simplest equlibrium question I have ever seen You know what the equlibrium CO2 pressure should be, so you know whether CO2 have to be asborbed by the CaO or produced from CaCO3. Case b is even simpler then simple  

[Ice-cream]

i don't get your explanation, can u please explain further becuase your talking about absorbing or producing CO2 but the question is asking about CaO so i don't the link between the two.

[Borek]

If the initial pressure of CO2 is larger than the equlibrium pressure CO2 will react with CaO to produce CaCO3. If the initial pressure is lower than equlibrium pressure, CaCO3 will decomopose (producing CaO and CO2) untill the CO2 pressure will reach equilibrium value. Thus looking at the pressure you can check whether it is too much or not enough CO2 and that translates directly into the changes in CaO amount.

[Ice-cream]

thanks Borek, i really wasn't thinking properly; i was making the Q more complicated than it really is!