Freezing takes place on lowering the temperature of a liquid substance. Substances have different freezing points because of different molecular structures.
In this article, we’ll cover
- Phases Of Matter
- Endothermic And Exothermic Process
- Role Of Latent Heat In Phase Transition
- How Freezing Is An Exothermic Process?
- Crystal Network In Freezing
- Kinetic And Cohesive Forces Between Molecules
- Changes In State Occur At Fixed Temperatures
- Energy Change In Change In State
- Effect Of Impurities
- Hydrogen Bonding In A Freezing Process
As we know very well, Matter is made up of small particles. These all small particles are also so minute that we cannot see with naked eyes.
Whenever heat is supplied to them they start moving from their original position. This heat energy is also represented as providing kinetic energy to the particles. On receiving heat this starts colliding with each other, if we keep on raising the temperature, at the end of this stage, they will turn themselves into another form.
The reverse is also true. On expelling the heat of a liquid, the internal energy and speed of particles slow down. Taking them to freezing point, this further becomes the reason for again the start of intermolecular forces.
You might have observed that when a cube of ice is taken out of a refrigerator, it melts into water. If this water is kept back in the refrigerator, it re-freezes into ice. This indicates that the properties of water and ice are the same, i.e. their chemical composition is the same. On melting of ice or on freezing of water no new substance is formed. Exothermic and endothermic process changes the physical state of the substance.
Is Freezing Endothermic Or Exothermic? Freezing is an exothermic process in which heat is expelled out. When the freezing process takes place the particles of a liquid substance slowly lose energy thus turns into a solid-state. Another name of freezing is solidification.
In another way, we can also explain it as liquid and gaseous particles have a weak force of attraction. To change them into a freezing solid state, a greater force of attraction is required. This can be achieved by lowering the heat. Extracting the heat from the substance allows liquid or gas particles to turn themselves into closed packed.
Phases Of Matter
Atoms are so small that they can only be seen with a powerful microscope. When atoms join together, they form molecules. The type of molecules determines the phase of matter. There are three common phases of matter: solid, liquid, and gas.
In a solid, such as a rock, the molecules are tightly packed together in a fixed shape. In a liquid, such as water, the molecules are close together but can move around. In a gas, such as air, the molecules are far apart and can move freely.
The fourth phase of matter is plasma, which is not as common on Earth but can be found in stars. In plasma, the molecules are separated into positive and negative ions. The four phases of matter can be changed into one another by adding or removing heat energy.
For example, water turns into steam when it is heated to high temperatures. The amount of heat needed to change a substance from one phase to another is called the melting point (for solids) or the boiling point (for liquids).substance from one phase to another is called the melting point (for solids) or the boiling point (for liquids).
Endothermic and Exothermic Process
Depending upon the energy absorbed or given out, reactions are of two types:
1. Exothermic reaction: Such reactions involves the given out of the heat.
2. Endothermic reaction: In these reactions, heat is absorbed to start the reaction and to change the state.
No matter whether physical or chemical, a reaction involves the breaking up of force of attraction or bonds between particles (atoms). During the physical process, with the release or absorption of energy, there is a change in state. Whereas in the chemical process, a new product is formed with the release or gain of energy.
These two types of energy are different from each other i.e. there is either a surplus or a deficit of energy during the reaction. Therefore, in chemical reaction energy is either absorbed or released.
The freezing process remains reversible through the endo and exothermic process. You have noted that when a cube of ice is taken out of a refrigerator, it melts and changes into water. It turns again into ice when put back in the refrigerator. This shows that on removing the cause of change the substance returns to its original state.
Role of Latent Heat In phase Transition
When water is heated, it doesn’t always immediately boil. Instead, it first goes through a phase of absorbing heat without undergoing any change in temperature. This is because the water molecules need to absorb a certain amount of energy before they can start to move around more quickly and turn into steam. This process of absorbing heat without changing temperature is known as latent heat.
The latent heat of vaporization is the specific amount of heat that water needs to absorb in order to vaporize. Once the water has absorbed this amount of heat, its temperature will start to rise again as it changes into steam. The latent heat of fusion is the specific amount of heat that water needs to absorb in order to melt. Once the water has absorbed this amount of heat, its temperature will remain constant as it changes from a solid to a liquid.
The latent heat of condensation is the specific amount of heat that steam needs to lose in order to condense back into water. Once the steam has lost this amount of heat, its temperature will start to fall again as it changes back into water. All three of these latent heats are important for understanding how energy is transferred during phase changes.
How Freezing Is An Exothermic Process?
As we said earlier, The heat we are giving to a matter is the kinetic energy and this energy certainly increases the particle collisions of the matter. What does this mean? Explaining in simpler words, this means that a gaseous state has more heat energy than a liquid and a liquid has more energy than a solid state.
When heat is supplied to a block of ice, it will turn into a liquid and when more heat is given to it, it will turn into a gaseous state.
During the process of freezing, heat is taken out from this substance. For example- When water is cooled it changes into ice. We can easily lower the temperature of the water by placing it into the refrigerator compartment. Water turns into ice because energy has been extracted from it which was a reason for being liquid. So that is why Freezing is an exothermic process.
You must remember that freezing is the reverse of melting. When water freezes to become ice when there is a change from a liquid state to a solid state.
Melting and freezing point of Water
If a teacher asks you about the Melting and freezing point of water then your answer should be zero degrees Celsius.
You also so bear in mind, the freezing point of a liquid is the same as the melting point of its solid form. When water is at zero degrees Celsius, it is the initial state when water starts to turn into ice. As the temperature becomes lower it will achieve a solid-state.
Similarly, the melting point of water is also zero degrees celsius. It is the temperature at which ice starts its changing state. The temperature keeps rising more, it will move towards a gaseous state as it is achieving more heat.
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Similarly, Instead of giving them the heat energy, if we take out heat from the substance, it also changes its state vice-versa.
crystal network in freezing
When water freezes, it forms a crystalline structure in which the molecules are arranged in a regular pattern. This process is known as crystallization. The resulting crystals are usually hexagonal in shape and have a symmetrical arrangement of molecules. The spacing between the molecules is relatively large, and this gives ice its low density. The open structure of ice also explains why it floats on water.
When water freezes, the kinetic energy of the molecules is reduced and they assume a more orderly arrangement. This process is known as freezing point depression. The freezing point of water is reduced by the addition of salt or other impurities. As the concentration of impurities increases, the freezing point decreases. This explains why salt is used to melt ice on roads and sidewalks.
By lowering the freezing point of water, salt makes it harder for ice to form. As a result, ice is less likely to form on roadways and sidewalks, making them safer for travel.
Kinetic and Cohesive Forces between molecules
When water molecules are in contact with one another, they are held together by cohesive forces. These forces arise due to the fact that water molecules are polarized, and the negative end of one molecule is attracted to the positive end of another molecule. However, water molecules also have kinetic energy, and this causes them to constantly move around and change position.
As a result, the cohesive forces between molecules are constantly breaking down and reforming. The balance between the cohesive and kinetic forces determines the state of a substance – whether it is a solid, liquid or gas.
In the case of water, the strong cohesive forces between molecules give rise to its liquid state. At room temperature, the kinetic energy of water molecules is high enough to overcome the cohesive forces, but not high enough for them to escape from the liquid entirely and enter the gas state.
Changes in State Occur at Fixed Temperatures
For a pure substance, a change in state occurs at a fixed temperature (provided we do not change the pressure). In all cases, 1 atmosphere is taken as the standard pressure.
Solid melts at a fixed temperature, called its melting point, and a liquid boils at a fixed temperature, called its boiling point. A liquid freezes at its freezing point and a gas (or vapour) liquefy at its temperature of liquefaction. Interestingly, the melting point of a solid is the same as the freezing point of the corresponding liquid. And the boiling point of a liquid is the same as the temperature of liquefaction of the corresponding gas.
The melting point and the boiling point of a pure substance are fixed at a particular pressure.
For example, at a pressure of 1 atmosphere, ice melts at 0°C and water freezes at 0°C, and water boils at 100°C and steam liquefies at 100°C. However, the melting point of solid decreases and the boiling point of a liquid increases with pressure.
Energy Change in Change in State
Energy change is a general feature of all changes–physical or chemical. So, a change in state is also accompanied by an energy change. This will be evident from the following observations.
1. If you put some ice in a glass, water droplets will collect on the outer surface of the glass. Ice needs heat to melt, which it takes from the surroundings. On giving heat to the ice, the water vapour in the air condenses on the outer surface of the glass. Reactions always involve an energy change. Let us look at a couple of illustrative examples.
In a reaction, suppose you need 500 kJ of energy to break the bonds of the reactants, but you get only 400 kJ of energy from the formation of the new bonds. So, you will have to spend 100 kJ of energy for the reaction to occur.
2. In another reaction, suppose you need 500 kJ of energy to break the bonds of the reactants, but you get 600 kJ of energy from the formation of new bonds. So, 100 kJ of energy will be released during this reaction.
In most cases, energy is absorbed or given out in the form of heat. However, in many cases, light is also absorbed or given out.
The effect of impurities on the melting point and the boiling point of a substance
The melting point and the boiling point of a substance change when soluble impurities are present in it.
When there are soluble impurities in a substance, its melting point is lowered. For example, sodium chloride is soluble in water, and so the melting point of water, in this case, ice) containing sodium chloride is lower than 0°C at 1 atmosphere. Mix some common salt with ice and record the temperature it will go to the minus side. This is the principle on which a freezing mixture works.
A freezing mixture is a mixture of ice and common salt or calcium chloride, and it helps us attain as low a temperature as -5°, -10° or -15°C, which may be required for an experiment. Ice-cream vendors store ice cream in a freezing mixture.
hydrogen bonding in A freezing process
Hydrogen bonds are one of the primary forces responsible for the freezing process. When water molecules come into contact with one another, they form hydrogen bonds. These bonds cause the molecules to stick together, creating a lattice-like structure. As more and more molecules join the lattice, the water becomes increasingly dense.
Eventually, the lattice is strong enough that it can no longer support the weight of the water above it, and the water freezes.
The hydrogen bonds also help to explain why ice is less dense than liquid water. The bond between each molecule is relatively weak, so the overall structure is not as compact as it could be. This explains why ice floats on water. Hydrogen bonding is a key force in many other processes as well, including cell biology and protein folding.
Is Freezing Endothermic Or Exothermic: Faqs?
What is solidification?
When a material changes from a liquid to a solid, it is said to have solidified. The molecules in a liquid are free to move around, but they are confined to a certain space. When a liquid changes to a solid, the molecules lose this freedom and become arranged in a fixed pattern. For example, when water freezes, the molecules arrange themselves into a crystal structure.
Solidification can occur due to cooling, as in the case of water, or due to an increase in pressure, as in the case of ice cubes made in an ice tray. Solids have a definite shape and volume, and they cannot be compressed. They also have lower entropy than liquids, meaning that they are more ordered. There are three main types of solids: crystalline solids, amorphous solids, and molecular solids. Crystalline solids have a repeating pattern of molecules, while amorphous solids do not. Molecular solids are held together by weak forces between molecules and have no definite shape.
ice freezing endothermic or exothermic
When water freezes, it undergoes a physical change from a liquid to a solid state. This process is exothermic, meaning that it releases heat energy into its surroundings. The freezing point of water is 32°F (0°C). As water cools and approaches this temperature, the molecules of water begin to slow down and stick together. Once the water reaches 32°F, the molecules are moving so slowly that they can no longer slip past each other and the water becomes a solid. This process results in the release of latent heat, which warms the surrounding air. While this might not seem like much, it’s actually enough to keep freshwater bodies from freezing solid in the winter. So next time you see ice on a pond or lake, remember that it’s helping to keep the water beneath it from freezing!