chem helpppppppp pleaseeeeeeeeeeeeeee?

Question

1. What is the enthalpy change, in Kj/mol, for the process below?
Ca^2+ (g) + 2Cl^- (g) --> CaCl2 (s)
Data (in kJ/mol):
Enthalpy of sublimation of Ca(s): 178
Bond dissociation energy of Cl2(g): 244
Ionization energies (1st, 2nd, 3rd) of Ca(g): 590; 1,145; 4,912
Ionization energies (1st, 2nd, 3rd) of Cl(g): 1,252; 2,297; 3,822
First electron affinity of Cl(g): -349
Standard enthalpy of formation for CaCl2(s): -796

2. Two elements, X and Y, form a crystalline material. The crystal lattice of this material can be described as follows. The X atoms form a cubic closest packed structure and the Y atoms occupy half of the tetrahedral sites in the lattice of X atoms.

The empirical formula of the solid is: X ____ Y ____

Old Science Guy · Accepted Answer

Ca (s) + Cl2 (g) ---> CaCl2 (s)  ∆H = -796  (standard formation)
...... .......Ca (g) ---> Ca(s)  .. ..∆H = -178  (opposite of sublimation)
.... .... .... Ca+2 ---> Ca (g) .. . ∆H = -1735  (opposite of ionizations 1st+2nd)
.. .. . ... 2 Cl (g) ---> Cl2 (g)  .. ∆H = -244   (opposite of dissociation)
.. .... .. 2 Cl- (g) ---> 2 Cl (g)  . ∆H = +698  (opposite of affinity and times 2 for 2 Cl's)
--------------------------------------------------------------------------------------------------------------------------
Ca+2 (g) + 2 Cl- (g) ---> CaCl2 (s)  ∆H = - 2255

this looks OK to me but check my math for sure

2
since there should be 4 tetrahedral sites per X
I think there should be 2 Y's per X
so
XY2
not dead certain but it seems logical

Anonymous · Answer

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chem helpppppppp pleaseeeeeeeeeeeeeee?

2 Answers