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Food in summer is more prone to spoilage, but keeping it in the refrigerator can extend the shelf life of the food; use a pressure cooker to cook the food, because the high temperature makes the cooking time shorter
.
It can be seen that temperature has a great influence on the rate of chemical reaction
According to the collision theory, when the temperature rises, the speed of molecular motion increases and the frequency of molecular collisions increases.
At the same time, the increase in the fraction of the activated molecular group increases the effective collision fraction of the molecules, so the reaction rate increases
.
According to the transition state theory, increasing the temperature increases the average energy of the reactant molecules, which is equivalent to reducing the activation energy value, so the reaction rate is accelerated
.
1.
The relationship between temperature and reaction rate constant
In 1901, the Dutchman van't Hoff pointed out that for every 10K increase in temperature, the reaction rate increased by 2 to 4 times
.
Two years later, HAArrhenius proposed the quantitative relationship between reaction rate and temperature.
In the formula, k is the reaction rate constant; A is the pre-factor; E a is the activation energy of the reaction
.
Since the rate constant k has an exponential relationship with the thermodynamic temperature T, a small change in temperature will cause a large change in the value of k
.
The logarithmic form of the Arrhenius formula is
The common logarithm form is expressed as
When using the Arrhenius formula to discuss the relationship between rate and temperature, it can be approximated that the activation energy E a and the pre-exponential factor A do not change with the change of temperature
.
The rate constant at temperature T 1 is k 1 , then
The rate constant at temperature T 2 is k a , then
Subtract and sort the two formulas, get
If the activation energy is known, the rate constant at another temperature can be obtained from the rate constant at a known temperature
.
The effect of temperature on the reaction rate is also manifested in different temperature ranges, and the multiples of the reaction rate increase when the temperature is increased
.
For example, when the activation energy E a =150kJ·mol -1 , the reaction temperature increases from 400K to 410K, and the ratio of k 2 to k 1 is 3.
0; the reaction temperature increases from 600K to 610K, and the ratio of k 2 to k 1 is 1.
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