If ΔS is negative, which statement is true?

If ΔS is negative, which statement is true?

• A. Products are more disordered than reactants
• B. Reactants are more disordered than products
• C. Entropy change is zero
• D. Enthalpy change is negative

Answer: (B)

Entropy reflects how disordered or spread out the energy is in a system. ΔS is defined as S_products minus S_reactants. A negative ΔS means the final state (the products) is more ordered than the initial state (the reactants). So the reactants are more disordered than the products, which is why the statement about reactants being more disordered is true. If the products were more disordered, ΔS would be positive; saying ΔS is zero would mean no change in disorder. The enthalpy change, meanwhile, relates to heat flow, not the disorder of the system, so it doesn’t determine the sign of ΔS.

Entropy reflects how disordered or spread out the energy is in a system. ΔS is defined as S_products minus S_reactants. A negative ΔS means the final state (the products) is more ordered than the initial state (the reactants). So the reactants are more disordered than the products, which is why the statement about reactants being more disordered is true. If the products were more disordered, ΔS would be positive; saying ΔS is zero would mean no change in disorder. The enthalpy change, meanwhile, relates to heat flow, not the disorder of the system, so it doesn’t determine the sign of ΔS.