Question

6. Given the following thermochemical reactions 2NO --N, +0, AH = -180 kJ 2NO+0, -2NO AH = -112 kJ Calculate the enthalpy change of the reaction of nitrogen with oxygen to produce nitrogen dioxide. N, +20, – 2NO, DH =?

Answer 1

Any given thermochemical reaction can be written in the opposite direction and the value of enthalpy change for that particular reaction will remain same but it will have opposite sign from the initial one.

Thus to calculate the enthalpy change for these reaction,sometimes we have to write the given thermochemical reaction in opposite direction by just changing the sign of enthalpy change value.The reaction has positive(+) enthalpy change value and hence it will be an endothermic reaction.

Given, 2NO -> N2+O2; AH = -180 KJ ------ 2 No +0₂ 2002 ; AH = -112 KJ ... (2) Woitting the equation no.co in opposite direction, we get, N₂ + O₂ 2N0 AH = + 180 KJ (3) By adding equation (3) & equation (1); we get N₂+O2 2NO, AN=+180 kJ 2 NO + O₂ → 2NO, AH = -112 KJ N2 + 20₂ 2NO, A N= (+180-112) KI 2 +68 KI . Enthalky change for the reaction, N₂ +202 2N02; will be +68kJ NO2 → 2N0 ; Alt = +68 kJ