Question

Choose the reactions (or processes) that are expected to have a positive value for ∆S°.

(Select all that apply.)

H₂O(l) → H₂O(s)

2N₂O₅(g) → 4NO₂(g) + O₂(g)

Fe(s) + 5CO(g) → Fe(CO)₅(l)

4NH₃(g) + 7O₂(g) → 4NO₂(g) + 6H₂O(g)

2NH₃(g) → N₂(g) + 3H₂(g)

Answer 1

entropy of gas > entropy of aqueous > entropy of liquid > entropy of solid

a)

There is liquid in reactant and solid in product.

Since liquid has more entropy, the reactant has more entropy here

So, entropy is decreasing in this reaction and ∆S° is negative

b)

There are 5 mol of gas in product and 2 mol of gas in reactant.

So, entropy increases

delta S is positive

c)

here gas is present on reactant side

So, entropy of reactant is more than product

so, entropy decreases

delta S is negative

d)

There are 10 mol of gas in product and 12 mol of gas in reactant.

So, entropy decreases

delta S is negative

e)

There are 4 mol of gas in product and 2 mol of gas in reactant.

So, entropy increases

delta S is positive

Answer: b and e