Activation Energy

At some point in our lives, we all have had difficulties waking up in the morning for school. Most of the times we needed some push from our parents to get out of the bed. The push that used to get us out of the bed was the activation energy for us. It gave us sufficient amount of energy, although energy here is more a psychological term than a physical one, it indeed was something that we required for sure in order to get out of the bed. There are many other things happening in and around us that require a fixed minimum effort in order to occur, some of which we notice and the others go unnoticed.

Activation Energy

What is Activation Energy?

Chemical Reactions are no different. Most of us must have experienced that it is difficult to start a vehicle during winters; it takes more time than usual. This is due to the fact that the energy of the fuel molecules decreases during winters as a result of low surrounding temperature. The molecules take time to reach a certain threshold energy where they can collide to undergo the combustion reaction and finally the vehicle starts moving. This threshold energy is called the activation energy.

All the reacting molecules in a chemical reaction that have kinetic energy equal to or greater than the activation energy and proper orientation undergo collisions that result in the formation of products. The molecules that have energy lower than activation energy will not be able to form products unless they cross this activation energy barrier. Activation energy is the barrier, which the reacting molecules must cross so that they can make effective collisions and form the products.

Mechanism of Activation energy

Activation Energy

Let us understand activation energy graphically. In the above figure, A and B are the reactants and C is the product. So A and B can from the product only if they cross the activation energy barrier. This barrier is the slight bump in the curve shown above. As we know that not all molecules have the same energy, so only those molecules that have sufficient energy (activation energy) can undergo effective collision that would result in the formation of the product C. By effective collision, it is meant that not all molecules having sufficient energy can form the products. Only those molecules that have both, sufficient energy and proper orientation, will collide to form the products. Activation Energy of reacting molecules is a prerequisite for a reaction to occur. This is the barrier they (the reacting molecules) must cross in order to effectively collide and form the product.

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Practise This Question

Read the following questions and answer as per the directions given below:

Statement – I: The first ionization energy of Be is greater than that of B.

Statement – II: 2p-orbital is lower in energy than 2s.