Please Help?

Question

For the reaction whose reactants and products are:



reactants: NH3 (g) O2 (g)


products: N2 (g) H2O (g)


calculate the standard entropy change (J/mol-K).

The answer depends on how you balance the equation. For this question balance the equation using the smallest ratio of WHOLE numbers.

Answer 1

First thing you need to do is balance the equation.

NH3 (g) + O2 (g) --> N2 (g) + H2O (g)

Remember: You want the same number of each element on both sides. You add / change the number in front the substance when you balance - don't change the subscripts / formulas.

Once you have a balanced equation you want to look up the entropies of formation for each substance in the equation. You probably have some tables of these in your chem book.

You use these entropies of formation in much the same way you have used enthalpies of formation. They're state functions so

change in S(reaction) = sum of Sf(products) - sum of Sf(reactants)

See Example 2 in the link below for how to use.