[panchi]

Calcium sulphate reacts with carbon (in the form of graphite) according to the reaction:
CaSO4(s) + 1/2C(s, graphite)  CaO(s) + SO2(g) + 1/2CO2(g)
When 204.2 g of CaSO4(s) reacts with excess graphite at 298.15 K and 1 atm pressure, 456
kJ of heat are absorbed. Calculate the standard molar enthalpy of formation of CaSO4(s).
.

[sjb]

456 kJ of heat for what quantity of CaSO₄?

[panchi]

for 204.2 g

[sjb]

for 204.2 g

How do you usually see molar enthalpies quoted? Also, do you have any other data?

[retracell]

First you determine the amount of moles of CaSO4(s) reacting.

204.2g/136.2g/mol = 1.5mol of CaSO4(s)

Then you can determine the standard heat of reaction

456kJ/1.5mol = 304kJ

Using the formula for standard heat of reaction you can determine the standard molar enthalpy of formation of CaSO4. You will need the standard enthalpies of formation for the other elements in order to calculate the the answer.