Enter an equation for the formation of NO2(g) from its elements in their standard states. Express your answer as a chemical equation. Identify all of the phases in your answer.

The standard state of the elements Nitrogen and Oxygen are N2 and O2, knowing that they are diatomic elements. With that piece of information, the unbalanced equation for the formulation of NO2(g) should be as follows -

N2 + O2 ---> NO2

And if you include their states -

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

To balance this chemical equation consider the number of reactants and products on other side of the equation. If you were to include a coefficient of one - half with respect to N2 on the reactant side, it would balance the reactants and products -