The standard enthalpy of formation (ΔH°f) is the enthalpy change that occurs when exactly 1 mol of a compound is formed from its constituent elements under standard conditions. The standard conditions are 1 atm pressure, a temperature of 25 °C, and all the species present at a concentration of 1 M. A "standard enthalpies of formation table" containing ΔH°f values might look something like this:
|
Substance
|
ΔH°f
|
|
H(g)
|
218 kJ/mol
|
|
H2(g)
|
0 kJ/mol
|
|
Ca(s)
|
0 kJ/mol
|
|
Ca2+(aq)
|
-543kJ/mol
|
|
C(g)
|
71 kJ/mol
|
|
C(s)
|
0 kJ/mol
|
|
N(g)
|
473 kJ/mol
|
|
O2(g)
|
0 kJ/mol
|
|
O(g)
|
249 kJ/mol
|
|
S2(g)
|
129 kJ/mol
|
What is the balanced chemical equation for the reaction used to calculate ΔH°f of CaCO3(s)?
If fractional coefficients are required, enter them as a fraction (i.e. 1/3). Indicate the physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively without indicating allotropes. Use (aq) for aqueous solution.
Express your answer as a chemical equation.