The first IE of lithium is 5.4eV and first electron affinity of Cl is 3.6eV. The value of ΔH for the reaction Li(g)+Cl(g)→Li+(g)+Cl−(g), is (in eV) :
A
+1.8
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B
+2.8
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C
−2.8
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D
+9
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Solution
The correct option is B+1.8 When lithium becomes a cation we give energy to the system. Hence energy is increased in the system and vice versa for chlorine i.e energy is released.
Hence energy is decreased from the system on the whole energy change is 5.4−3.6=1.8.