Final answer:
An endothermic reaction requires additional energy from outside the system to reach the transition state, as it absorbs energy, typically as heat, from its surroundings to provide the activation energy needed.
Step-by-step explanation:
The type of chemical reaction that requires additional energy from outside the system to reach the transition state is a endothermic reaction. Endothermic reactions absorb energy, typically as heat, from their surroundings, which is necessary for the reactants to transform into products. This additional energy is needed to provide the activation energy that "pushes" the reaction to proceed, and without it, the reactants would not have enough energy to overcome the activation barrier and the reaction would not occur.
Examples of endothermic processes include photosynthesis and the dissolution of salts in water. Conversely, an exothermic reaction is one that releases energy, such as when burning paper (combustion) and cellular respiration. Enzymes can facilitate these reactions by reducing the activation energy required, thereby making the reactions proceed more quickly.