Temperature Dependence on Rate of Reaction

Effect of Temperature on Rate of Reaction

Till now we know that temperature influences the rate of a reaction. If the temperature increases the rate of reaction increases and if the temperature decreases the rate of reaction decreases. If we took an example that the time taken to melt a metal will be much higher at a lower temperature but it will decrease if we increase the temperature. Reaction kinetics is one of the most advanced studies in the field of physical chemistry, and it deals with the study of chemical reactions or processes. The engineers and scientists get help from the information about these factors affecting the rate of a chemical reaction to economically scale up the reactions to industrial scale in various industries.  Therefore it is very important for us to know how the rate of a chemical reaction gets affected.


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Effect of Temperature

The rate of a chemical reaction can be affected by one of the parameters that is temperature. We have seen milk boiling on a gas stove. On the flame of the stove, the rate of a specific quantity of milk boils depends. The milk boils in less time if the flame height is maximum, and the milk takes more time to boil if the flame height is minimum. Here the flame height resembles the temperature.


Temperature dependence of the rate constant:


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The equation is,

K =  Aexp(-Ea /RT)

K = The rate constant of the reaction

A = The Arrhenius Constant

Ea = Activation Energy for the reaction (in Joules mol−1)

R = Universal Gas Constant

T = Temperature in absolute scale (in kelvins)

lnk = -(Ea/R)(1/T) + lnA


The milk attains its boiling point in less time, if the temperature is high, and the milk takes more time to attain its boiling point, if the temperature is low. That is not the only reaction that gets affected by temperature. Most of the chemical reactions in their reaction rate show a change with the varying in temperature. for every 10oC rise in temperature, The rate constant for a chemical reaction gets doubled.  


If we see the other effect of temperature, when we cook, if we keep the gas at a low temperature, the food cooks slowly. But if we increase the temperature, to its maximum, the food cooks quickly. Therefore the rate of reaction got increased by the temperature. By the Arrhenius equation, this dependence of rate on temperature can be explained. Let’s learn about and deduce this equation.


Arrhenius Equation

Svante Arrhenius extended the work of J.H Van’t Hoff in 1889 and proposed an equation that relates temperature and the rate constant for a reaction quantitatively. The proposed equation is known as the Arrhenius Equation. 

Here is the equation on the temperature dependence of the rate of a chemical reaction which is known as the Arrhenius Equation.

K =  Aexp(-Ea /RT)

Where,

K = The rate constant of the reaction

A = The Arrhenius Constant

Ea = Activation Energy for the reaction (in Joules mol-1)

R = Universal Gas Constant

T = Temperature in absolute scale (in kelvins)

We knew that the rates of reaction increase with an increase in temperature but it was not known on how to predict the relation between temperature and reaction rates quantitatively. Arrhenius Equation has enabled us to overcome this problem. It is an empirical relation that is used to model the variation of the rate constant with the temperature, which in turn gives information about the rates of chemical reactions at different temperatures.


Fun Facts

  1. If the temperature increases the rate of reaction increases and if the temperature decreases the rate of reaction decreases.

  2. If we took an example that the time taken to melt a metal will be much higher at a lower temperature but it will decrease if we increase the temperature.

  3. Going back to the rate law equation, it follows that a higher rate of constant results in a higher reaction rate. This makes sense because as temperature increases, molecules move faster and collide more frequently, resulting in an increased fraction of molecules with higher energy than the activation energy. 

  4. Due to chemical bonds having been broken and made, they also usually give out or take in energy such as heat or light because. It reacts with oxygen in water or in the air to create a new compound called iron oxide (rust), when iron rusts. No mass is lost or gained in every chemical reaction due to change in temperature.

FAQ (Frequently Asked Questions)

1. How does Temperature Affect the Rate of a Chemical Reaction?

The chemical reactions occur more rapidly at higher temperatures, It is common knowledge. Due to the temperature as the average kinetic energy of a particle increases, the particles move faster and collide with each other more frequently per unit time and possess greater energy when they collide. In another way, if the temperature is increased, it speeds up the motion of molecules, so they are more likely to bump into each other and react. Both of these factors increase the reaction rate. With increasing temperature the reaction rate of virtually all reactions increases.


The molecular energy levels also increase, causing the reaction to proceed faster, when the temperature of a solution increases.

2.  Why do Chemical Reactions Occur More Slowly at Low Temperatures?

For the rate of reaction of any particles, the temperature is a very important factor, this factor can increase or decrease a chemical reaction. The reacting particles have less kinetic energy when a reaction is being done by us at a lower temperature (particles move faster when they are being heated). As a result due to low temperature, they collide with each other less frequently. That's why the reaction happens at a slower rate.