Introduction:
Chemical reactions involve the breaking and formation of chemical bonds between atoms. In order for a reaction to occur, the reactant molecules must overcome a certain energy barrier called activation energy. The activation energy is the minimum energy required to initiate a chemical reaction.

Explanation:
The chemical reactions in which reactants require a high amount of activation energy are generally slow. This is because a higher activation energy means that the reactant molecules need more energy to reach the transition state, where the bonds are in the process of breaking and forming.

Factors affecting reaction rate:
The rate of a chemical reaction is determined by several factors, including the concentration of reactants, temperature, surface area, and the presence of a catalyst. However, the activation energy plays a crucial role in determining the speed of the reaction.

Activation energy and reaction rate:
The activation energy can be thought of as a barrier that reactant molecules must overcome in order to react. The higher the activation energy, the slower the reaction will be. This is because a higher activation energy requires more energy to be supplied to the reactant molecules, which can be achieved through an increase in temperature.

Reaction profiles:
A reaction profile is a graphical representation that shows the energy changes that occur during a chemical reaction. The reactants are shown on the left side, and the products are shown on the right side. The energy of the reactants is represented by the starting point of the reaction profile, and the energy of the products is represented by the ending point.

Reaction profiles for slow and fast reactions:
For a slow reaction, the reactants require a high activation energy to reach the transition state, as shown by a steep uphill slope on the reaction profile. The reaction proceeds slowly, as the reactant molecules need to collide with enough energy to overcome the activation energy barrier.

In contrast, for a fast reaction, the reactants require a low activation energy to reach the transition state, as shown by a shallow uphill slope on the reaction profile. The reaction proceeds quickly, as the reactant molecules can easily overcome the activation energy barrier.

Conclusion:
In conclusion, the chemical reactions in which reactants require a high amount of activation energy are generally slow. The activation energy acts as a barrier that the reactant molecules must overcome in order to react. The higher the activation energy, the slower the reaction will be. It is important to note that other factors such as concentration, temperature, surface area, and the presence of a catalyst also influence the reaction rate.