Question

Calculate the change in entropy if Br2(l) is converted into gaseous Br atoms.

S° for Br2(l) = 152.2 J/(mol•K)

S° for Br2(g) = 245.5 J/(mol•K)

S° for Br(g) = 175.0 J/(mol•K)

Answer 1

197.8 J/mol

Step-by-step explanation:

The conversion will happen in steps. First, the Br₂(l) will be converted to Br₂(g), and then to Br atoms. Thus, the change in entropy will be the sum of the change in entropy of the two steps.

Step 1

Br₂(l) → Br₂(g)

ΔS = ∑n*S°products - ∑n*S°reactants, where n is the stoichiometric coefficient

ΔS = 245.5 - 152.2 = 93.3 J/K

Step 2

Br₂(g) → 2Br(g)

ΔS = (2*175.0) - 245.5 = 104.5 J/mol

Thus, the total change in entropy is

ΔS = 93.3 + 104.5

ΔS = 197.8 J/mol

Answer 2

197.8 J/(mol•K).

Step-by-step explanation:

• ∆S° = [Σ bS° products] - [Σ aS° reactants], where b and a are the coefficients of the products and the reactants in the balanced reaction equation.

Br₂(l) ⟶ 2 Br(g)

∴ ∆S° = [2 x S° Br(g)] - [S° Br₂(l)]

∴ ∆S° = [(2)(175.0 J/(mol•K)] - [152.2 J/(mol•K)] = 197.8 J/(mol•K).