Matter transforms from one state to another in various ways. In science, all possible changes can be classified into two broad categories. 1. Physical change 2. Chemical change.
We all know that physical changes are those changes that do not change their composition and no new product is formed. Whereas chemical changes are those changes in which a new product is formed. When it comes to melting, It is a physical change.
Melting of a substance is a change that alters temporarily in some or all of its physical properties, viz. state, shape, size, appearance, etc., but not in its chemical composition.
There are countless melting examples we see in our daily routine. Out of several few are melting ice (snow), chocolate, butter on a hot pan, burning a candle, etc.
One most common example of melting is ice cream. Ice cream tastes so good. It is sweet, delicious. When we purchase a softy ice cream, in winters, it does not melts whereas, in summers, it quickly melts.
During the winters season, the surrounding temperature is lower and frozen ice cream scoop does not change its state to liquid.
Melting ice cream is an endothermic process in which heat is taken in from the surroundings. In summers, ice cream melts so rapidly. It absorbs the heat from the surroundings tends to attain equilibrium till the temperature equals the environment.
If ice cream is at zero degrees celsius and environment temperature is at 25 degrees Celcius. It is the tendency of ice cream to keep on gaining heat till it has equal temperature to its surroundings. The state where the temperature becomes equal is called the equilibrium state.
However, on placing ice cream in a refrigerator compartment. It starts losing heat and does not melt as it wants to achieve the fixed temperature of the refrigerator.
Melting is a phase when a solid substance transforming itself into a liquid state. The state can be easily altered by changing parameters like temperature, pressure, etc.
Is Melting Endothermic or Exothermic? Melting is an endothermic process in which heat is consumed from an external source. During the process, there is no rise in temperature only the heat supplied to overcome the force of attraction so that they become somewhat loose and form a liquid state.
As we said earlier, in the melting process, there is a conversion of solid into a liquid.
- The heat energy given to the solid is absorbed by its particles and thus, gaining kinetic energy.
- An endothermic process happens, the kinetic energy gained by the particles, increase the rate of vibration of particles.
- The kinetic energy of the particles overcome the force of attraction, and thus, the particles from the surface of solid becomes free and hence the state changes from solid to liquid.
Moving further, We all are surrounded by so many things. And that things are changing with time. Few of them are slow while others are fast changing. Such as deterioration of houses is a slow process whereas burning paper is a fast process.
It is interesting to note that all these changes are happened due to changing temperature pressure under various circumstances. In addition to this, science has divided these changes into two parts physical changes as well as chemical changes.
What is Endothermic Process?
The endothermic process when procced requires energy to complete the reaction. It is interesting to note that energy utilized by the reactants is quite less than the energy used by the products.
Such kind of reactions needs some external source energy to initiate the process otherwise it cannot be sustained.
In addition to this, while writing the chemical reaction for endothermic processes we always add + heat on the reactant side.
Reactants+ Heat → Product
Ice +Heat → Water
What is Exothermic Process?
Exothermic reactions are those reactions when proceeding heat energy is evolved. In the case of exothermic, the energy of the reactants is more than the energy of the product. During the process, the total energy required to break the bonds is far less than the energy released in the formation of new products.
During writing the chemical reaction, along with the products taking part in a reaction we also have to include + heat symbol along with it.
Reactants→ Product+ Heat
Water → Ice+Heat
Why Melting is Endothermic Process?
Generally, the transfer of heat to make a solid into liquid can takes place in three ways. Conduction, convection, and radiation. The endothermic melting process can take place in any of the ways.
Now, the question arises that when heat is absorbed, where does goes? The answer is this heat is utilized to overcome the force of attraction between the particles.
As we know very well particles of solid substance attract each other with strong intermolecular forces. This force of attraction holds the particles closely packed. The heat which we supply to a substance to melting is all used to overcome the force of attraction between particles. This makes the force of attraction become loose and forms a liquid state. The heat does not raise the kinetic energy of particles. That’s why melting is an endothermic process.
The higher the force of attraction among the particles of the substance, the more heat is required to melt. For example, the ice has a melting point of 0 C whereas the drinking water glass melts at 1700 C, this clearly, shows in the endothermic process, massive heat is absorbed by the glass particles to overcome the force of attraction among the particles whereas ice needs negligible relatively.
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Melting Of Ice Cubes Endothermic Process
Snow or ice melts to water at zero degrees Celcius. However, the composition remains the same. Just like other substances, the melting of ice is also an endothermic process in which thermal energy changes the state to water. Ice cube molecules have enough energy to change the state to water. After ice turns to water, it still has zero degrees celsius. It doesn’t mean that it does not have any energy, yes, it has energy but this heat energy is only limited to change the state. This heat basically called the latent heat of fusion where the temperature is constant.
It is interesting to note that the melting point of ice can be changed easily by adding an impurity. Adding a pinch of salt to the water and freeze. This lowers the freezing temperature, keeps it cooler, and makes ice cubes long-lasting. Salt act as a restrictor that prevents ice from melting.
If the temperature value is negative, it means it is below zero degrees celsius. Inside heat exists but not of that much quantity that can make molecules change their state. When we raise the temperature to 0 degrees Celsius, it is a point where ice changes into a liquid. Water does not have the heat itself to change its temperature value to more.
If we supply more heat, The particles of the material after consuming heat get excited and start striking with the other adjacent particles. This changes the state of matter from a solid to a liquid having more temperature than 0 degrees celsius.
Holding ice cube – When we place a piece of ice in our hand we feel very cold. Steadily, the ice on a hand starts melting. Ice cubes are acquiring heat from our hands. This lowers the temperature of the hand.
The heat has the tendency to move from higher temperature to lower. Ice cubes at low temperature taking in the heat the equal temperature of the heat supplier hand. As we said before the transfer of heat can take place in three ways. Here, the heat supplied is through conduction.
Melting of wax– Weigh a beaker containing some solid wax on a beam balance. Melt the wax and again weigh the beaker. You will find that the two weights are identical. This shows that there is no change in the mass of the substance involved as a result of physical change.
When a solid substance melts it absorbs heat to form a liquid. Its reverse is also true. it is experimentally verified when the liquid freezes to form a solid an equal amount of heat is given out. The heat is supplied to a substance is calculated in joules per kg.
no gain or loss of energy
Solid substance (ice) changes into steam by absorbing a certain amount of heat energy. The same amount of energy is given out when water changes back into the ice by giving up its heat.
Therefore, we can say that there is no net gain or loss of energy as a result of the melting process. The characteristics of melting can be summarized as follows:
- No new substance is formed.
- There is no change in the chemical composition of the original substance.
- The change is temporary and it can be reversed by reversing the conditions.
- The change is only in the state, size, shape, colour, texture or the smell of some or all of the substances that undergo physical change.
- There is no change in the masses of the substances involved in a melting phase.
- There is usually no loss or gain of energy as a result of melting change.
The molecules of matter are in constant motion. In a solid, the molecules only vibrate about the same position, somewhat the way we jog in place. When a solid is heated, the molecules vibrate with greater energy, which shows a rise in temperature. The molecules also gain enough energy to move apart a little, which results in expansion or melting.
The more a solid is heated, the more energetically its molecules move. In other words, the more its temperature rises. Then there comes a point when the molecules become energetic enough to change their positions relative to each other. That is when a solid melts. The temperature at which this occurs depends on the strength of the cohesive force that binds the molecules of a solid. In general, the cohesive force that binds a metal is stronger than that which binds a nonmetal, so metals have a higher melting point than nonmetals.
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