Identify the true statement. A spontaneous reaction must have (a)...

Question

Identify the true statement. A spontaneous reaction must have (a) a negative enthalpy change. (b) a positive enthalpy change. (c) a positive entropy change. (d) a positive free-energy change. (e) a negative free-energy change.

Accepted Answer

Step 1: Understand the concept of spontaneity in chemical reactions. A spontaneous reaction is one that occurs naturally under given conditions without needing external energy input.. Step 2: Recall the Gibbs Free Energy equation: $ \Delta G = \Delta H - T \Delta S $, where $ \Delta G $ is the change in free energy, $ \Delta H $ is the change in enthalpy, $ T $ is the temperature in Kelvin, and $ \Delta S $ is the change in entropy.. Step 3: For a reaction to be spontaneous, the change in Gibbs Free Energy ($ \Delta G $) must be negative. This is the key criterion for spontaneity.. Step 4: Analyze each option: (a) A negative enthalpy change ($ \Delta H < 0 $) can contribute to spontaneity but is not a requirement. (b) A positive enthalpy change ($ \Delta H > 0 $) does not necessarily prevent spontaneity if $ T \Delta S $ is large enough. (c) A positive entropy change ($ \Delta S > 0 $) favors spontaneity but is not a requirement. (d) A positive free-energy change ($ \Delta G > 0 $) indicates non-spontaneity.. Step 5: Conclude that the correct statement is (e) a negative free-energy change ($ \Delta G < 0 $) is required for a reaction to be spontaneous.