Question

Which of the following standard enthalpy of formation values is not zero at 25°C?

A. H₂(g)
B. O₂(g)
C. N₂(g)
D. CO₂(g)

Answer 1

The enthalpy of formation for CO₂(g) is -393.5 kJ/mol at 25°C, while the enthalpies of formation for H₂(g), O₂(g), and N₂(g) are all zero at this temperature. Hence the correct answer is option D

Step-by-step explanation:

The standard enthalpy of formation of any element in its standard state is zero. This means that the enthalpy of formation of H₂(g), O₂(g), and N₂(g) is zero at 25°C. However, the enthalpy of formation of CO₂(g) is not zero at 25°C and is equal to -393.5 kJ/mol.

Hence the correct answer is option D