(ii) Which side of the reaction is favored by entropy? (iii) If ∆S° = 0 for these reactions, calculate ∆G° (Assume T = 298 K) [BDE for O―H = 110 kcal /mol.]
(b)

검증된 단계별 안내

Step 1: Understand the concept of entropy (∆S°). Entropy is a measure of disorder or randomness in a system. Reactions that increase the number of gas molecules or increase disorder are generally favored by entropy. Analyze the reaction to determine if the products or reactants have greater entropy.

Step 2: For part (ii), compare the number of molecules and phases (solid, liquid, gas) on both sides of the reaction. If the products have more gas molecules or a higher degree of disorder, the reaction is favored by entropy on the product side. If the reactants have more gas molecules or disorder, the reaction is favored by entropy on the reactant side.

Step 3: For part (iii), use the Gibbs free energy equation:

∆G° = ∆H° - T∆S°

. Since ∆S° = 0 is given, the equation simplifies to

∆G° = ∆H°

. Focus on calculating ∆H° using bond dissociation energies (BDEs).

Step 4: Calculate ∆H° by summing the BDEs of bonds broken in the reactants and subtracting the BDEs of bonds formed in the products. For example, if an O―H bond is broken, use the given BDE value of 110 kcal/mol. Ensure you account for all bonds involved in the reaction.

Step 5: Once ∆H° is calculated, substitute it into the simplified Gibbs free energy equation

∆G° = ∆H°

to determine the value of ∆G°. This will indicate whether the reaction is thermodynamically favorable (negative ∆G°) or not (positive ∆G°).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Entropy (S)

Entropy is a measure of the disorder or randomness in a system. In chemical reactions, an increase in entropy typically favors the formation of products, as systems tend to move towards greater disorder. Understanding how entropy changes during a reaction helps predict which side of the reaction is thermodynamically favored.

Gibbs Free Energy (∆G)

Gibbs Free Energy is a thermodynamic potential that indicates the spontaneity of a reaction at constant temperature and pressure. It is calculated using the equation ∆G = ∆H - T∆S, where ∆H is the change in enthalpy, T is the temperature in Kelvin, and ∆S is the change in entropy. A negative ∆G indicates a spontaneous reaction, while a positive ∆G suggests non-spontaneity.

Bond Dissociation Energy (BDE)

Bond Dissociation Energy is the energy required to break a specific bond in a molecule, resulting in the formation of free radicals. In the context of the question, knowing the BDE for the O―H bond allows for the calculation of energy changes associated with breaking and forming bonds during the reaction, which is essential for determining ∆G°.

(ii) Which side of the reaction is favored by entropy? (iii) If ∆S° = 0 for these reactions, calculate ∆G° (Assume T = 298 K) [BDE for O―H = 110 kcal /mol.] (b)