Which of the following relations represents the temperature coefficient of a reaction ?

Options

A. `r_(t+10)/r_(t)`
B. `(t_(k))/(t_(t)+10)`
C. `k_(t+10)/k_(t)`
D. `(E_(a)-K_(t+10))/(E_(a)+K_(t))`

Answer

C

Explanation

The temperature coefficient of a reaction gives the number of times the rate of a reaction increases by a rise in temperature of `10^(@)C` It is expressed as ther ratio of the rate constants of a reaction at two different temperatureas (usually `35^(@)C` and `25^(@)C`) differing by `10k` . Thus
Temperature coefficient `=(k_(35^(@))/(k_(25^(@)`
The temperature coefficient of most of the reactions is positive and lies between `2` and `3` .
A reaction whose temperature coefficient is negative is
`2NO(g)+O_(2)(g)rarr2NO_(2)(g)`
Thus, the rate of this reaction decreases with increases of temperature. It can be explained following:
Reaction Mechanism
`2NO(g)rarrN_(2)O_(2)(g)`
`N_(2)O_(2)(g)rarr2NO_(2)(g)`
At higher temperature more `N_(2)O_(2)` molecules are dissociated. The lower concentration of `N_(2)O_(2)` molecules at higher temperature result in decrease of reaction rate.