enthalpy of formation

Calculate the enthalpy of formation of magnesium sulphide given the following data.

mg²⁺ + s^2- ->mgs H= -3255kj
Mg(s) --> mg (g) H= +150kj
mg (g) -> mg⁺ + e- H= +736kj
mg+(g) --> mg²⁺ (g) +e- H= +1450kj
S(s) -> s(g) H= +223kj
S(g) + e- --> s- (g) H= -200
S-(g) + e- --> S^2- H= +532kj

How do I work this out?

Reply 1

Christophicus

18

stratomaster

Calculate the enthalpy of formation of magnesium sulphide given the following data.

mg²⁺ + s^2- ->mgs H= -3255kj
Mg(s) --> mg (g) H= +150kj
mg (g) -> mg⁺ + e- H= +736kj
mg+(g) --> mg²⁺ (g) +e- H= +1450kj
S(s) -> s(g) H= +223kj
S(g) + e- --> s- (g) H= -200
S-(g) + e- --> S^2- H= +532kj

How do I work this out?

Have you heard of born haber cycles?

Reply 2

stratomaster

OP

yes but i've missed some of the work.. do i need to draw the cycle out?

Reply 3

Christophicus

18

stratomaster

yes but i've missed some of the work.. do i need to draw the cycle out?

Yes, with these problems you have to draw the cycle out and work from there. Every compound is different.

To help you:
DIRECT ROUTE = INDIRECT ROUTE

Enthalpy of formation of MgS
= Lattice energy of MgS + enthalpy of atomisation of Mg + enthalpy of atomisation of S + 1st IE of Mg + 2nd IE of Mg + 1st EA of S + 2nd EA of S