ClNO Decomposition at Room Temperature

 

Question

At room temperature (25 °C), the gas ClNO is impure because it decomposes slightly according to the equation 2ClNO(g) –> Cl2(g) + 2NO(g)

The extent of decomposition is about 4%. Based upon this, the approximate value of ΔG°298 for the reaction at that temperature.

 

Answer

2 ClNO → Cl2 + 2 NO

Let’s assume the total volume is 1L.

If we start with 100 moles of ClNO, at equilibrium 4 moles will decompose into 2 moles of Cl2 and 4 moles of NO

At equilibrium:

[ClNO] = (100-4)/1 = 96 M

[Cl2] = 2/1 = 2 M

[NO] = 4/1 = 4 M

Keq= [NO]2 x [Cl2]/ [ClNO]2

ΔG0= – RT.Ln(Keq) = – RT.Ln([NO]2 x [Cl2]/ [ClNO]2)

ΔG0= – 8.341 x (273 + 25) x Ln (42 x 2/962) = 14.1 kJ

ΔG0= 14.1 kJ

 

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