[utramos]

Calculate a lattice energy for CaH2 using the following information.

Eea for H = -72.8 kJ/mol
Ei1 for Ca = +589.8 kJ/mol
Ei2 for Ca = +1145 kJ/mol
heat of sublimation for Ca = +178.2 kJ/mol
bond dissociation energy for H2 = +435.9 kJ/mol
net energy change for the formation of CaH2 from its elements = -186.2 kJ/mol


My work

Ca(s)-> Ca (g) for

178.2 kj/mol

Ca(g)->Ca+ for

589.8kj/mol

Ca+ -> Ca2+ for

1145 kj/mol

H2(g)-> H2(g) for

435.9 kj/mol

H-> H- for

( -72.8*2 )

(Ca2+) + 2H- „³ CaH2 for

-U

[/u]
Net change -186.2 kj/mol


-U= -178.2-589.8-1145-435.9+(72.8*2)-186.2 = -2389.5 kj/mol

U= 2389.5 kj/mol

What am I doing wrong here?

[Donaldson Tan]

Eea for H = -72.8 kJ/mol

Is that the enthalpy for 1st electron affinity?

[utramos]

yes that is the energy change when an electron is added to an isolated atom in the gaseous state

[xiankai]

Ca²⁺ + 2H^- --> CaH₂ ... - U

why is it negative? is not lattice energy the amount of energy contained when gaseous ions form a compound?

[Donaldson Tan]

Construct the Bon-Haber Cycle first.

[utramos]

Got it just have a messed up sig fig when i was doing the problem thanks