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Explain the effect of temperature on reaction rate based on Arrhenius theory. |
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Answer» Solution :(i) Generally, the RATE of reaction increases with increasing temperature. However, there are very few exceptions. (ii)As a rough rule , for many reaction near room temperature reaction rate tends tu when the temperature is increased by `10^@ C` (iii)A large number of reaction are known which do not take place at room temperature occur readily at higher temperatures . Example : Reaction between `H_2 and O _2`to from `H_2O` takes place only when an electric spark is passed. (IV) Arrhenius suggested that the rates of most reaction vary with temperature in such a WAY that the rate constant is directly proportional to `e^(-(E_a)/(RT))`and the proposed a relation between the rate constant and temperature . `k=Ae^(-(E_a)/(RT))` where k = frequency factor`""...(1)` R = gas constant T = Absolute temperature (in kelvin) The factory A does not vary significantly with temperature and HENCE it may be taken as a constant . TAKING logarithm on both side equation (1) ln `k = ln A + ln e^(-E_a//RT)` ln `k = lnA - E_a/(RT)[:. ln e = 1]` ln k `= ln A - E_a/R (1/T)` (vi) The plot of lnk vs `(1/T)` is a straight with negative slope `E_a/(RT)` . If the rate constant for a reaction at two different temperatures is known , we can calculate the activation energy ln `k_2 - ln k_1 -[E_a/(RT_2)]+[E_a/(RT_1]]`This equation can be used to calculated `E_a` from rate constants `k_1 &k_2` at temperature `T_1 and T_2` . |
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