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diff --git a/3856/CH20/EX20.2/Example20_2.sce b/3856/CH20/EX20.2/Example20_2.sce
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+//Calculate the Lattice energy of Sodium Chloride
+
+//Example 20.2
+
+clc;
+
+clear;
+
+n=8.4; //Integer between 8 and 12( For the repulsive term in the lattice)
+
+NA=6.022*10^23; //Avogadro's number in mol^-1
+
+mew=1.7476; //Madelung constant for the NaCl crystal lattice 
+
+e=1.602*10^-19; //Charge on electron in C
+
+epsilion=8.854*10^-12 //Molar extinction cofficient in C^2 N^-1 m^-2
+
+r=2.81*10^-10;  //Sum of radii of Sodium ion and Chlorine ion in m
+
+Vbar=-((NA*mew*e^2)/(4*%pi*epsilion*r))*(1-(1/n)); //Lattice energy in J mol^-1(conversion factor 1J=1N m)
+
+U=-Vbar/1000;  //Lattice energy in kJ mol^-1
+
+printf("Lattice energy of Sodium chloride = %.0f kJ mol^-1",U); 
diff --git a/3856/CH20/EX20.2/Example20_2.txt b/3856/CH20/EX20.2/Example20_2.txt
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+ Lattice energy of Sodium chloride = 761 kJ mol^-1
+\ No newline at end of file