Enthalpy of Formation (1 Viewer)

[nimrod_dookie]

Any help with the following question would be greatly appreciated.

Calculate the enthalpy of formation of hydrated magnesium chloride solid.

Mg + Cl2 + +6H2 +3O2 -----> MgCl2.6H2O

The following information is needed to calculate the answer.

H2 +Cl2 +aq --------> 2HCl Enthalpy=-334 kJ

2H2 +C2 ------> 2H2O Enthalpy= -570 kJ

 

[Jumbo Cactuar]

well the answer is -2499 kJ/mol ...

... though I know you need more information than what you have given.

Did you previously react HCl aqueous with Magnesium metal and calculate the enthalpy change for that process?

---- Mg + Cl2 +6H2 +3O2 = state A
|...................|
|...................| see below
|...................v
|....Mg + 2HCl + 6H2O - H2 = state B
|...................|
|...................| calculated previously
|...................v
--->MgCl2.6H2O = state C

now, enthalpy is known as a state function; that is that the EoF doesn't depend on how a system got there.

so;

dH(A->C) = dH(A->B) + dH(B->C)
= 3 * -570 - 334 + N kJ/mol
= - 2044 + N kJ/mol

so your previously collected data should be about -455 kJ/mol.

 

[nimrod_dookie]

Thankyou so much.

 

[s_t_a_r1234]

does enthalpy mean the amount of energy stored within a substance
and also what does system mean and also state of function