What is Activation energy in chemical reactions?

• A. The energy released during a reaction
• B. The energy absorbed to raise the temperature
• C. The minimum energy required to start a reaction
• D. The energy stored in the reactants

Answer: (C)

Activation energy is the minimum energy that reacting molecules must have to start a chemical reaction, allowing them to reach the transition state where bonds are broken and new bonds form. This energy barrier shows up on an energy diagram as the peak between reactants and products. Not every collision leads to a reaction—only those with enough energy to overcome this barrier can proceed. The activation energy is different from the overall energy change of the reaction (the heat released or absorbed), and it’s not the energy stored in the reactants. Catalysts lower this barrier by providing an alternative pathway, so more collisions have enough energy to overcome it, which speeds up the reaction. Temperature affects how many molecules have sufficient energy to cross the barrier through the distribution of molecular energies.