Some things burn while others melt when subjected to heat. Curious observation!! Have you ever wondered why this happens? Which we will discuss in our article today. To make things easier for our audience who are already in science that burning and melting are two different phenomena.
Burning of things or materials is a chemical process and melting is related to a scientific phenomenon known as a phase transition. You must have seen that we light a candle, the wick of the candle burns while wax(fuel) melts. Burning here is purely a chemical and thermodynamic process while wax melting is the phase transition.
For better understanding, let’s take an example of burning a piece of wood and melting ice. When you burn a piece of wood to ashes see if you can turn it into wood again?. No, You can’t, it’s an irreversible chemical phenomenon. But ice, when melted in water, can be made into ice again. This is a phase change.
To fully understand why some things burn while some melts, we must first understand the process of phase transition.
Phase transition is the phenomenon that describes the transition between solids, liquids, and gases. Sometimes it is also of utility in studying such a phenomenon related to the plasma state. Please note that a phase of a thermodynamic system will have a similar property related to the state of matter. A phase transition is said to occur when certain properties of the medium change (such as wax melting) due to changes in external factors such as temperature change and pressure etc.
A phase transition is classified into two parts: Ehrenfest classification and Modern classification
The Ehrenfest classification is put forward by Paul Ehrenfest. According to this classification step, the closures at the transition were labeled by the lowest derivative of free energy that is discontinued at the transition. In this classification, the solid/liquid/gas transitions are called the first-order phase transition.
A highlighting feature of the first-order phase transition is the closed change in the variable. While the transition variable is continuous in the second-order phase. We will not go into details here but will clearly mention that the Ehrenfest classification is not correct and has some flaws. it will not be possible to discuss them in our present article. Modern imperfections have developed due to these flaws.
In modern classification, the first-order transition is governed by the theory of latent heat. During such a transition, the system either releases or absorbs a certain amount of energy according to the given volume. here the temperature of the system remains constant as the heat increases. This means that the excess heat is turned off during the process. In modern classification, the second-order is called a continuous phase transition. This is a very complex phenomenon to study. But it is more concrete than earlier classification.
Now you know the basics of phase transition, Its time to understand the answer to the question which this article want to solve. See, any substances that have a combustion temperature that is lower than the melting point will burn instead of melt.
They react with the oxygen in the atmosphere and perform combustion (burn) before they have a chance to change their phase. On the other hand, materials that have a higher combustion temperature than their melting point will initiate the phase transition process and melt (change their phase). It’s as simple as that.
I hope this completes the answer you guys were looking for.