Question

define standard enthalpy of formation . write a chemical equation for the formation of N2O5.

Answer 1

standard enthalpy of formation is defined as the enthalpy change when 1 mole of a compound/substance at STP is formed from its elemtal state.

Answer 2

Explanation :

Standard enthalpy of formation : It is defined as the enthalpy change when the one mole of a compound is formed from its element in the standard state.

The standard elemental state of nitrogen is, $N_2$ and the standard elemental state of oxygen is, $O_2$

The balanced chemical equation for the formation of $N_2O_5$

$N_2(g)+\frac{5}{2}O_2(g)\rightarrow N_2O_5(g)$