Question

The minimum energy level required for an effective collision is called __________ (threshold/collision) energy

Answer 1

Hint: An effective collision is a collision which leads to the forward direction of the reaction. In other words, effective collision leads to the formation of the products.

Complete step by step answer:
This question is based on two important concepts. Typically, what you need is the concept about the two terms that is given to fill in the blanks. Before that, let’s take a look at an effective collision.

We can see from the above image that \[{H_2}\] & \[C{l_2}\] are colliding to form \[HCl\] molecules. Now, this is a good example where effective collision has been taken. If the collision was not effective, then the product \[HCl\] would not have formed. It would stay as \[{H_2}\] & \[C{l_2}\] only.

Coming back to the question, first let’s take a look at the term threshold energy. The word threshold literally means the minimum of something that is needed for a particular cause. Similarly, threshold energy is the minimum energy required for a particular energy to occur. Threshold energy is also known as the activation energy. And you can also see from the above picture that the activation energy or threshold energy barrier must be crossed for a reaction to occur.
And a collision energy is any energy that is released in a collision. This collision energy does not guarantee that a reaction would occur. The energy must cross the threshold energy for having an effective collision. So, collision energy does not fulfil the “minimum energy level” criteria.
Hence, the answer to this question is that threshold energy is the minimum energy level required for an effective collision.

Note:
There is also a concept regarding the orientation of the molecules. It also plays a vital role for the reaction to occur. If the molecules are not properly oriented, it would not lead to an effective collision.