A process is always spontaneous under which conditions?

• A. positive ΔS and positive ΔH
• B. negative ΔS and positive ΔH
• C. positive ΔS and negative ΔH
• D. negative ΔS and negative ΔH
• E. no process is always spontaneous

Answer: (C)

Verified step by step guidance

1. Understand the concept of spontaneity in thermodynamics: A process is spontaneous if it occurs without needing to be driven by an external force. The spontaneity of a process is determined by the Gibbs free energy change (ΔG).
2. Recall the Gibbs free energy equation: ΔG = ΔH - TΔS, where ΔG is the change in Gibbs free energy, ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.
3. Identify the conditions for spontaneity: A process is spontaneous when ΔG < 0. This means that the change in Gibbs free energy must be negative.
4. Analyze the given conditions: For ΔG to be negative, if ΔH is negative (exothermic process) and ΔS is positive (increase in disorder), then ΔG will be negative at all temperatures, making the process always spontaneous.
5. Evaluate the options: The correct condition for a process to be always spontaneous is when ΔS is positive and ΔH is negative, as this ensures ΔG is negative regardless of the temperature.