A chemical reaction that occurs on its own without the input of additional energy is described as

• A. Spontaneous
• B. Non-Spontaneous
• C. Activation Energy
• D. Activated Complex

Answer: (A)

Spontaneous reactions are those that can proceed on their own without continual energy input. This depends on the overall change in Gibbs free energy: if ΔG is negative under the given conditions, the reaction is thermodynamically favored and tends to proceed. However, even spontaneous reactions often require a little initial energy to overcome the activation energy—the energy barrier to reach the transition state. Once past that barrier, the reaction can continue without extra energy input. The activated complex is simply the high-energy arrangement at the top of that barrier, seen during the reaction pathway, not a description of spontaneity. Reactions with positive ΔG are non-spontaneous and need continuous energy input to occur.