Activation energy is the amount of kinetic energy required to propagate a chemical reaction under specific conditions within a reaction matrix. Activation energy is a blanket term that's used to quantify all of the kinetic energy that can come from different sources and in various energy forms. Temperature is a unit of measure for heat energy, and as such, temperature affects the ambient and above ambient kinetic environment of a reaction.
Temperature in and of itself is nothing more than a quantification of heat energy. Being a measure of energy, temperature can be used as one of what could be several energy input paths that help a reaction matrix reach its activation energy. Higher or lower temperature raises and lowers the further energy requirements to achieve a reaction.
There are different types of temperatures, such as Kelvin, Celsius and Fahrenheit. These temperature types are nothing more than different scales in which thermal energy is measured--each scale with its own per-unit density of thermal kinetics. As such, chemical reaction activation temperature is usually expressed in Joules, with any thermal temperature values converted from their respective scales to Joules units.
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Generally speaking, the activation energy of a reaction is above ambient energy levels within any reaction matrix. This activation energy level can be reached by adding electrical, light, thermal and other forms of energy. As more energy is generally required for a reaction to occur, raising the temperature brings a reaction closer to its activation energy requirement. Reducing heat usually serves to retard a reaction.
As chemical reactions occur, it's common for exothermic mechanisms to take place. These produce heat and thus increase the temperature and reaction rate as a corollary. This exponential effect is of great concern, as an increasing reaction rate may cause unpredicted energy output and lead to a loss of reaction control or damage to the reagents within the matrix itself.
As with all chemistry-related reaction mechanisms, great care should be taken when applying thermal energy or reducing it from a reaction. Reducing beyond a certain point may cause material loss or even excessive secondary reaction products. Furthermore, excessive temperature may also result in further reaction convolution, which can lead to undesirable reaction products and even personal injury if the reaction reaches a flash point.