Question

In which of the following processes/processes heat is released?
A. Condensation
B. Vaporisation
C. Freezing
D. Melting

Answer 1

As a very first step, one could talk about the processes where heat is released in general and also recall the name given to this class of processes. Now, you could define all the given processes and check for the chance of release of heat in each of them and hence answer the question.

Complete step-by-step solution:
In the question, we are given four processes and we are asked to find which among them is an exothermic process, that is a process where heat energy is released.
Let us first discuss exothermic processes.
The class of reactions where the overall standard enthalpy change is found to be negative is called the exothermic reaction. That is, in these reactions, heat is released. The reactions that are just opposite this, are called endothermic reactions, where heat energy is absorbed.
Now let define the given processes.
Condensation is the process by which matter changes its physical state from gaseous state to that of liquid state and it is also known to be opposite to the process of vaporization. So, when matter changes from liquid to gas, it is said to be vaporised. Freezing is the process by which liquid changes its state to solid and melting is when solid liquifies.
Among the four, only condensation is known to result in the release of heat. And hence, Option A is the answer.

Note: Enthalpy is the term given to describe the energy of a chemical system. So, the heat transferred in and out of a closed system at a constant pressure could be termed enthalpy change. Thermite reaction, combustion, combining strong acids and bases are some examples of exothermic reactions.