Purists might note that the symbol used to represent the difference between the free energies of the products and the reactants in the above figure is G o , not G o. A small capital "G" is used to remind us that this diagram plots the free energy of a pair of molecules as they react, not the free energy of a system that contains many pairs of molecules undergoing collision.
If we averaged the results of this calculation over the entire array of molecules in the system, we would get the change in the free energy of the system, G o. Purists might also note that the symbol used to represent the activation energy is written with a capital " E ".
This is unfortunate, because it leads students to believe the activation energy is the change in the internal energy of the system, which is not quite true. E a measures the change in the potential energy of a pair of molecules that is required to begin the process of converting a pair of reactant molecules into a pair of product molecules. Aqueous solutions of hydrogen peroxide are stable until we add a small quantity of the I - ion, a piece of platinum metal, a few drops of blood, or a freshly cut slice of turnip, at which point the hydrogen peroxide rapidly decomposes.
This reaction therefore provides the basis for understanding the effect of a catalyst on the rate of a chemical reaction. Four criteria must be satisfied in order for something to be classified as catalyst.
A small quantity of catalyst should be able to affect the rate of reaction for a large amount of reactant. The first criterion provides the basis for defining a catalyst as something that increases the rate of a reaction. The second reflects the fact that anything consumed in the reaction is a reactant, not a catalyst. The third criterion is a consequence of the second; because catalysts are not consumed in the reaction, they can catalyze the reaction over and over again.
In order for the reaction to occur. Why does increasing the concentration of a sample generally increase the rate of a reaction? How can I draw a simple energy profile for an endothermic reaction in which 50 kJ mol-1 is What do you understand by the activation energy of a reaction? See all questions in Collision Theory. Impact of this question views around the world.
For a generic reaction. So here we have two different contribution to free energy. One is entropic or temperature dependent contribution that comes from vibrational, rotational, and translational partition function, and temperature independent contribution from electronic partition function.
Even zero point energy is also temperature independent. Electronic partition function is temperature independent as long as they are in ground state.
Activation energy has a term that is proportional to temperature according to transition state theory at least. This relies on the definition of activation energy as the parameter. Sign up to join this community. The best answers are voted up and rise to the top.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Is activation energy temperature-independent? Ask Question. Asked 5 years, 9 months ago. Active 3 years, 3 months ago. Viewed 20k times. Improve this question. Mithoron 4, 12 12 gold badges 36 36 silver badges 55 55 bronze badges. The temperature dependence is usually small, but not zero. This can be seen from, for example, transition state theory analysis. For various other reasons it may in fact be large, e.
If both A and B are gases, the frequency of collisions between A and B will be proportional to the concentration of each gas. If we double the concentration of A, the frequency of A-B collisions will double, and doubling the concentration of B will have the same effect.
Therefore, according to collision theory, the rate at which molecules collide will have an impact on the overall reaction rate.
When two billiard balls collide, they simply bounce off of one other. This is also the most likely outcome when two molecules, A and B, come into contact: they bounce off one another, completely unchanged and unaffected. In order for a collision to be successful by resulting in a chemical reaction, A and B must collide with sufficient energy to break chemical bonds. This is because in any chemical reaction, chemical bonds in the reactants are broken, and new bonds in the products are formed.
Therefore, in order to effectively initiate a reaction, the reactants must be moving fast enough with enough kinetic energy so that they collide with sufficient force for bonds to break. This minimum energy with which molecules must be moving in order for a collision to result in a chemical reaction is known as the activation energy. As we know from the kinetic theory of gases, the kinetic energy of a gas is directly proportional to temperature.
As temperature increases, molecules gain energy and move faster and faster. Therefore, the greater the temperature, the higher the probability that molecules will be moving with the necessary activation energy for a reaction to occur upon collision. Even if two molecules collide with sufficient activation energy, there is no guarantee that the collision will be successful.
In fact, the collision theory says that not every collision is successful, even if molecules are moving with enough energy. The reason for this is because molecules also need to collide with the right orientation, so that the proper atoms line up with one another, and bonds can break and re-form in the necessary fashion. For example, in the gas- phase reaction of dinitrogen oxide with nitric oxide, the oxygen end of N 2 O must hit the nitrogen end of NO; if either molecule is not lined up correctly, no reaction will occur upon their collision, regardless of how much energy they have.
However, because molecules in the liquid and gas phase are in constant, random motion, there is always the probability that two molecules will collide in just the right way for them to react. Of course, the more critical this orientational requirement is, like it is for larger or more complex molecules, the fewer collisions there will be that will be effective.
An effective collision is defined as one in which molecules collide with sufficient energy and proper orientation, so that a reaction occurs. According to the collision theory, the following criteria must be met in order for a chemical reaction to occur:. Collision theory explanation : Collision theory provides an explanation for how particles interact to cause a reaction and the formation of new products.
The rate of a chemical reaction depends on factors that affect whether reactants can collide with sufficient energy for reaction to occur.
Explain how concentration, surface area, pressure, temperature, and the addition of catalysts affect reaction rate. Raising the concentrations of reactants makes the reaction happen at a faster rate. For a chemical reaction to occur, there must be a certain number of molecules with energies equal to or greater than the activation energy.
With an increase in concentration, the number of molecules with the minimum required energy will increase, and therefore the rate of the reaction will increase. For example, if one in a million particles has sufficient activation energy, then out of million particles, only will react. However, if you have million of those particles within the same volume, then of them react.
By doubling the concentration, the rate of reaction has doubled as well. Experiment with changing the concentration of the atoms in order to see how this affects the reaction rate the speed at which the reaction occurs. In a reaction between a solid and a liquid, the surface area of the solid will ultimately impact how fast the reaction occurs.
This is because the liquid and the solid can bump into each other only at the liquid-solid interface, which is on the surface of the solid.
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