Energy to break bond

Dissociation reactions, such as HCl(g) - H(g) + Cl(g), require energy to break bonds and therefore are endothermic with positive AH values. The AS values for such reactions are positive since 2 or more particles are being formed from 1 molecule, causing the system to become more energetically dispersed. Under the circumstances when AH and AS are both positive, the spontaneity of the reaction is favored at higher temperatures. 

Since irregular structure elements (point defects) such as interstitial atoms (ions) or vacancies must exist in a crystal lattice in order to allow the regular structure elements to move, two sorts of activation energies have to be supplied from a heat reservoir for transport and reaction. First, the energy to break bonds in the crystal... 

Some molecules only catch glancing blows low energy collisions with too little energy to break bonds. So no reaction ... 

If it takes more energy to break bonds in the Markovnikov product, it must be lower in energy, therefore, more stable—OPPOSITE OF STABILITY OF THE INTERMEDIATES ... 

Pyrolysis reactions are one class of reactions that benefit from the use of an SCF solvent medium since the SCF can solubilize reacted products and remove them from the high-temperature zone, thus avoiding further thermal decomposition. The carbon formation that occurs at the high temperatures normally encountered in pyrolysis reactions can therefore be minimized. Improved yields, selectivities, and product separation have been attained in an SCF reaction medium, compared with conventional pyrolysis methods. There is no doubt that a sufficiently high temperature is needed to provide the thermal energy to break bonds in a pyrolysis reaction. But it is not necessary to operate at excessively high temperatures to increase the vapor pressure of the product materials because the SCF medium has the necessary solvent strength to dissolve the products and remove them from the reaction zone. 

It is easy to see why reactions speed up when the concentrations of reacting molecules are increased higher concentrations (more molecules per unit volume) lead to more collisions and so to more reaction events. But reactions also speed up when the temperature is increased. Why The answer lies in the fact that not all collisions possess enough energy to break bonds. A minimum energy called the activation energy ( ) is needed for a... 

The reason that a reaction occurs faster as the temperature is increased is that the speeds of the molecules increase with temperature. So at higher temperatures, the average collision is more energetic. This makes it more likely that a given collision will possess enough energy to break bonds and to produce the molecular rearrangements needed for a reaction to occur. 

On a molecular level, reaction rates depend on the frequency of collisions between molecules. The greater the frequency of collisions, the higher the reaction rate. For a collision to lead to a reaction, however, it must occur with sufficient energy to break bonds and with suitable orientation for new bonds to form in the proper locations. We will consider these factors as we proceed through this chapter. 

---