Question

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

(Select all that apply.)

4Al(s)ﾠ+ﾠ3O₂(g) → 2Al₂O₃(s)

NaCl(s) → Na⁺(aq) + Cl^-(aq)

CH₃OH(g) + ³/₂O₂(g) → CO₂(g) + 2H₂O(l)

SiO₂(s) + 3C(s) → SiC(s) + 2CO(g)

I₂(g) → I₂(s)

Answer 1

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

a)

There are more gases on reactant side.

So, entropy is decreasing in the process.

Hence delta S is negative

b)

These are aqueous component in product but solid in reactant.

So, entropy is increasing.

Hence delta S is positive

c)

There are more gases on reactant side.

So, entropy is decreasing in the process.

Hence delta S is negative

d)

There are more gases on product side.

So, entropy is increasing.

Hence delta S is positive

e)

There are more gases on reactant side.

So, entropy is decreasing in the process.

Hence delta S is negative

Answer: a, c, e