Question

The enthalpy for the decomposition of nitrogen dioxide into molecular nitrogen and oxygen

2NO2 (g) - N2 (g) + O2 (g)

is:

A) 67.6 kJ
B) -67.6 kJ
C) 293.8 kJ
D) -293.8 kJ
E) 45.5 kJ

Answer 1

The enthalpy for the decomposition of 2 moles of NO2 into N2 and O2 is -66.4 kJ, with the closest answer choice being B) -67.6 kJ, likely due to rounding differences.

Step-by-step explanation:

The enthalpy for the decomposition of nitrogen dioxide (NO2) into molecular nitrogen (N2) and oxygen (O2) can be derived using standard enthalpies of formation. For NO2(g), the standard enthalpy of formation is +33.2 kJ/mol, which means that the formation of 1 mol of NO2(g) from N2 and O2 releases 33.2 kJ of energy. The decomposition reaction we are interested in is the reverse of the formation reaction, and we are dealing with 2 moles of NO2(g).

Overall, the enthalpy change for the reaction 2NO2 (g) → N2 (g) + O2 (g) will be twice the enthalpy of formation but with the opposite sign:

2 x (+33.2 kJ/mol) = +66.4 kJ (for the formation of 2 moles of NO2)

For the decomposition, the enthalpy change will be the negative of this value:

ΔH = -66.4 kJ

Therefore, the enthalpy for the decomposition of 2 moles of NO2 into N2 and O2 is -66.4 kJ. The closest answer choice is B) -67.6 kJ, which likely accounts for rounding differences in the provided choices.