The specific heats of iodine vapour and solid are 0.031calK−1g−1 and 0.055calK−1g−1 respectively. If heat of sublimation of iodine is 24 cal/g at 200∘C, calculate its value at 250∘C.
A
5.7calg−1
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B
11.4calg−1
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C
22.8calg−1
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D
45.6calg−1
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Solution
The correct option is C22.8calg−1 Solid I2 is converted into I2 vapour I2(s)→I2(g)ΔH=24cal/gat200∘CΔCp=(Cp)I2(g)−(Cp)I2(s)=0.031−0.055=−0.024calg−1K−1
From Kirchhoff's equation, ΔH250∘−ΔH200∘C=ΔCp(T250∘−T200∘)ΔH250∘C=24−0.024(523−473)=24−1.2=22.8calg−1