Question

Construct a Born-Haber cycle and calculate the lattice energy of CaC2 (s). Note that this solid contains the diatomic ion C22–.

Useful Information:
?H°f (CaC2(s)) ?Hsub (Ca (s)) ?Hsub (C (s)) Bond dissociation energy of C2 (g) = +614 kJ/mol
First ionization energy of Ca (g) = +590 kJ/mol Second ionization energy of Ca (g) = +1143 kJ/mol First electron affinity of C2 (g) = –315 kJ/mol Second electronaffinity of C2 (g) = +410 kJ/mol
= –60 kJ/mol = +178 kJ/mol = +717 kJ/mol

Answer 1

Useful Information:

?H°f (CaC2(s)) = –60 kJ/mol
?Hsub (Ca (s)) = +178 kJ/mol
?Hsub (C (s)) = +717 kJ/mol
Bond dissociation energy of C2 (g) = +614 kJ/mol
First ionization energy of Ca (g) = +590 kJ/mol
Second ionization energy of Ca (g) = +1143 kJ/mol
First electron affinity of C2 (g) = –315 kJ/mol
Second electron affinity of C2 (g) = +410 kJ/mol


I HAVE WORKED THIS OUT TO BE LE(NACI) = 4011Kj/Mol

Answer 2

Reaction : C2-2 (g) + Ca2+(g) .............> CaC2 (s)


1. Ca(s) ...........> Ca(g) ; ?H01 = +178kJ/mol

2.Ca(g) ..............> Ca+(g) ; ?H02 =+590kJ/mol

3. Ca+(g) ............>Ca2+(g) ; ?H0 3 =+1143kJ/mol

4. 2C(s) ...............>2C (g) ; ?H0 4 =+717kJ/mol

4a. 2C(g) .............> C2(g) ?H0 4a = -614kJ/mol
5. C2 (g) + e ...........>C21- (g) ; ?H0 5= -315kJ/mol

6. C21- (g) + e ..........>C22- (g) ; ?H0 6 = +412kJ/mol

7. Ca2+(g) + C22-(g) ..............> CaC2 (s) ; ?H0 7 = ?(Lattice energy)
...............................................................................

?Hf = ?H01 + ?H02 +?H0 3 + ?H0 4 +?H0 4a + ?H0 5 +?H0 6 + ?H0 7

? ?H0 7 = ?Hf -{?H01 + ?H02 + ?H03 + ?H0 4 + ?H0 4a + ?H0 5 + ?H0 6}
= -60 kJ/mol - {(+178kJ/mol) +(+590kJ/mol )+(+1143kJ/mol)+ (+717kJ/mol) +(-614kJ/mol) + (-315kJ/mol)+(+412kJ/mol)}

= - 2171kJ /mol