Final answer:
The energy barrier impedes the reaction of thermodynamically unstable reactants, and reaching the transition state is necessary for the reaction to occur. The transition state is a high-energy and unstable configuration that molecules achieve when they have sufficient kinetic energy to overcome the activation energy.
Step-by-step explanation:
The energy barrier slows the progress of thermodynamically unstable reactants. Reactant molecules that reach the peak of this barrier are in the transition state, which is a high-energy, unstable state. The concept of an energy barrier is central to understanding chemical reactions and involves the activation energy, which must be exceeded for a reaction to proceed. Reacting molecules must possess at least this minimum amount of energy to overcome electrostatic repulsion and break chemical bonds, allowing new bonds to form. This energy threshold was first postulated by the Swedish chemist Svante Arrhenius. At the top of the energy hill in a reaction coordinate diagram, you can find the transition state, also known as the activated complex — a temporary arrangement of atoms that will either form the products of the reaction or revert back to reactants.
Temperature significantly affects the kinetic energy of molecules, thereby influencing the reaction rate. Higher temperatures increase the fraction of molecules that have energy greater than the activation energy (Ea), leading to a higher likelihood of overcoming the energy barrier. This illustrates why reactions tend to occur more rapidly at elevated temperatures.