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The increased speed of a simple bimolecular change when temperature of the reaction mixture is increased.

Temperature  usually has a major effect on the rate of a chemical reaction. Molecules at a higher temperature have more thermal energy. Although collision frequency is greater at higher temperatures. When the temperature of reaction mixture is increased, the kinetic energy of molecules increases which results in increase in velocity of molecules which in turn, results in increase in number effective, collisions; Consequently the speed of bimolecular change get increased.
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How can the rate of a fast reaction be determined by Flash Photolysis?

Flash photolysis: When we pass a powerful flash of short duration or laser beam, through the reaction mixture to initiate a reaction the atoms, ions or free radicals are formed.
These atoms, ions or free radicals formed can be identified by passing a second, Flash of light through the mixture immediately after the first flash.
For this the absorption spectrum of the mixture is monitored continuously at small regular intervals after first flash and the changes in the spectrum with time indicate the various processes occurring in the system.
It can also be studied by observing some other property like electrical conductance or magnetic property of the reaction mixture.

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One gram of pulverized wood burns faster than one gram piece of wood.

The rate of reaction depend upon the surface are a of reacting species. Pulverized wood has greater surface area as compared to one gram of piece of wood so it comes in contact with oxygen to much more extent and get burnt much faster.
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The action of a solid phase catalyst to increase the rate of unimolecular gas—phase decomposition reaction.


A catalyst is a substance that accelerates the rate of a chemical reaction but remain chemically unchanged afterwards.The unimolecular gases gets absorbed over the catalyst and form activated complex, which gets changed into decomposed products easily.
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How does temperature affect the rate of a reaction? Is there a corresponding equal decrease in number of collisions among molecules of a gaseous reaction? How is this effect explained by the concept of activation energy?

Temperature usually has a major effect on the rate of a chemical reaction. Molecules at a higher temperature have more thermal energy. Although collision frequency is greater at higher temperatures. When the temperature of reaction mixture is increased, the kinetic energy of molecules increases which results in increase in velocity of molecules which in turn, results in increase in number effective, collisions; For every 10°C rise in temperature the rate of the reaction becomes double-fold to five-fold. There is no corresponding increase in the number of collision among the gaseous molecules because for 10°C rise in temperature the increase in number of collisions is only 2 to 3 percent. This many fold increase in the rate of the reaction is explained by the concept of activation energy. Only those collisions are effective and result in the formation of product where the molecules possess a certain minimum amount of energy over and above their average energy which is called the activation energy. For every 10°C rise in temperature, the number of activated molecules increase by 200 to 500% and therefore the reaction rate becomes double to five fold.
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