Question

The molar heat of formation of NH₄NO₃ (s) is −367.54 kJ and those of N₂O (g), H₂O (l) are 81.46 and −285.8 kJ respectively at 25°C and atmosphere pressure. The difference of ΔH and ΔE of the reaction \[\ce{NH4NO3(s) -> N2O (g) + 2H2O (l)}\] is ______ kJ.

Options

• 2.324

• 4.897

• 6.782

• 9.781

Answer 1

The molar heat of formation of NH₄NO₃ (s) is −367.54 kJ and those of N₂O (g), H₂O (l) are 81.46 and −285.8 kJ respectively at 25°C and atmosphere pressure. The difference of ΔH and ΔE of the reaction \[\ce{NH4NO3(s) -> N2O (g) + 2H2O (l)}\] is 2.324 kJ.

Explanation:

Molar heat of formation are:

NH₄NO₃ (s) = –367.54 kJ

N₂O (g) = 81.46 kJ

H₂O (l) = –285.8 kJ

\[\ce{NH4NO3(s) -> N2O (g) + 2H2O (l)}\]

`"∆H"_"reaction" = ∑"H"_"P" – ∑"H"_"R"`

= [81.46 + 571.6] – [–367.54]

= –490.14 + 367.54

= –122.6 kJ

and ∆H = ∆E + ∆ng RT

∆H = `"∆E" - 1 xx (8.31 xx 298)/(1000)`

∆E = `"∆E" - (1) xx (8.31 xx 298)/1000`

= –122.6 – 2.476

= –125.076 kJ

∆H – ∆E = –122.6 – (–125.076) = 2.324 kJ