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Born-Haber cycle: MgCl2
The Born-Haber cycle can by divided into stages like the ones in the table below. Start by filling in the table
using:
−
Mg (g) + 2Cl (g) MgCl2(s)
2+
Mg(s) + Cl2(g)  MgCl2(s)
Mg(g)  Mg (g) + 2e
2+
standard enthalpy
change(s)
stage
∆H
elements to gaseous atoms
θ
at Mg
& 2∆H
equation(s)
Mg(s)  Mg(g)
θ
at Cl
Cl2(g)  2Cl(g)
−
nd
Mg(g)  Mg (g) + 2e
2 x 1 EA of Cl
st
2Cl(g) + 2e  2Cl (g)
gaseous ions to solid lattice
lattice enthalpy (formation)
Mg (g) + 2Cl (g) 
MgCl2(s)
elements to compound
∆H f MgCl2
st
atoms to positive ions
1 + 2 IE of Mg
atoms to negative ions
−
2+
−
−
2+
θ
−
Mg(s) + Cl2(g)  MgCl2(s)
Problem Solving Gridlock 1
Each row, column and 2 x 2 box contains information about the first four stages listed. Use your problem
solving skills and the answers in the table above to fill in the blank boxes.
stage
standard enthalpy change(s)
atoms to positive ions
atoms to negative ions
lattice enthalpy
(formation)
gaseous ions to solid
lattice
elements to gaseous
atoms
1 + 2 IE of Mg
2 x 1 EA of Cl
1 + 2 IE of Mg
atoms to negative ions
gaseous ions to solid
lattice
lattice enthalpy
(formation)
elements to gaseous
atoms
atoms to positive ions
∆H
θ
at Mg
st
& 2∆H
θ
at Cl
2 x 1 EA of Cl
st
nd
standard enthalpy change(s)
st
∆H
nd
θ
at Mg
& 2∆H
θ
at Cl
st
stage
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Gridlock 2
Each row, column and 2 x 2 box contains information about each of the last four stages listed.
stage
equations
atoms to positive ions
gaseous ions to solid
lattice
2Cl(g) + 2e  2Cl (g)
atoms to negative ions
elements to compound
Mg (g) + 2Cl (g) 
MgCl2(s)
Mg(s) + Cl2(g) 
MgCl2(s)
2Cl(g) + 2e  2Cl (g)
−
−
−
2+
−
−
−
Mg (g) + 2Cl (g) 
MgCl2(s)
2+
st
2+
lattice enthalpy
(formation)
nd
θ
−
∆H f MgCl2
equations
−
Mg(g)  Mg (g) + 2e
1 + 2 IE of Mg
Mg(g)  Mg (g) + 2e
2+
Mg(s) + Cl2(g) 
MgCl2(s)
2 x 1st EA of Cl
standard enthalpy change(s)
Gridlock 3
You will need to work out which stages are in this gridlock.
stage
equations
elements to compound
elements to gaseous
atoms
Mg(g)  Mg (g) + 2e
gaseous ions to solid
lattice
atoms to positive ions
Mg(s) + Cl2(g) 
MgCl2(s)
Mg(s) + Cl2(g) 
MgCl2(s)
lattice enthalpy
(formation)
Mg(s)  Mg(g)
Cl2(g)  2Cl(g)
−
Mg(g)  Mg (g) + 2e
2+
−
Mg (g) + 2Cl (g) 
MgCl2(s)
equations
2+
−
2+
∆H
θ
at Mg
& 2∆H
θ
at Cl
−
Mg (g) + 2Cl (g) 
MgCl2(s)
2+
Mg(s)  Mg(g)
Cl2(g)  2Cl(g)
st
1 +2
nd
IE of Mg
θ
∆H f MgCl2
standard enthalpy change(s)