Enthalpy and calcium carbonate?

Question

Ok, heres the questions:
How is the enthalpy of formation of calcium carbonate different from the enthalpy of decomposition of calcium carbonate?

What would the chemical equation for the enthalpy of formation of calcium carbonate be?

and...

What standard conditions are used to get the standard enthalpy of formation for calcium carbonate ?

Help please.... I'm really stuck, thank you.

Answer 1

Entalpy of formation:

Ca + C + 1.5 O2 ----> CaCO3

The Ca must be a solid, the C must be graphite, the O2 must be a gas and you must specify the temperature (usually 298K).

Decomposition:

CaCO3 -----> CaO + CO2