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You might have observed how an ice cube melts at room temperature to become water or how water boils to eventually transform into vapor and evaporate. These changes in matter are known as changes of state. But why does matter does so? The matter might change states when it absorbs or releases energy. These changes do not involve any change or alteration in the chemical properties of the substance involved. In this article, we will have a look at the change of state of matter, the reason behind it, and the various processes involved.
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Keyterms: Cubes, Vapor, Evaporate, Liquid, Solid, Gas, Thermal energy, Heat, Atoms, Energy, Melting point, Boiling Point
Read More: States of Matter
Change of State
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Matter usually exists in three states which are solids, liquids, and gases. The change of the substance from one state to another is termed a change of state. Two common changes of state accommodate the change from solid to liquid and from the liquid state to vapor/gas and vice versa.
When a substance absorbs a certain amount of energy, its atoms and molecules move in a rapid manner due to which its kinetic energy increases. This increase in kinetic energy helps in pushing the particles farther apart from each other, hence the substance changes form. The energy of the substance in this state is known as thermal energy or heat.
Heat and Change of State of Matter
Also Read:
| Important Links | ||
|---|---|---|
| Specific Heat Capacity by Method of Mixtures | Latent Heat | Heat Vs Temperature |
| Thermal Conductivity of Copper | Thermal Energy | Conversion of Energy |
The Change of State from Solid to Liquid
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The change of state of a substance from solid to liquid is known as melting. Until all of the solid substance melts, the temperature of the system remains constant. Hence, both the solid and liquid states of matter exist with each other in thermal equilibrium during the transition state. Here, the temperature at which both these states coexist is known as its melting point. Melting Point is a special property of the substance which also depends on the pressure. At standard atmospheric pressure, the melting point of a substance is known as its normal melting point.
The process of melting and freezing of water
The change of state from liquid to solids is known as freezing and the point at which the liquid and solid state exist in thermal equilibrium is known as the freezing point. When the pressure around a substance is increased, the freezing point also increases. It’s easier to keep solid substances under great pressure. As the molecules of solids are closely packed together, they are denser than liquids. Through freezing, the molecules of the substance are compacted further in a much smaller space
For instance,
Over a slab of ice, if we put a metallic wire with two blocks of equal weight attached at both ends, we will observe that the metallic wire passes through the ice slab. This result is because due to an increase in pressure, the ice below the wire melts at lower temperatures.
A metallic wire with equal weights tied on both of its ends placed on top of an ice slab
When the wire passes through the slab, the water freezes to render ice again. This phenomenon of the metallic wire passing through the ice slab without splitting it in two parts is known as regelation. This makes skating on snow possible as the snow below skates due to high pressure transforms into water and therefore acts as a lubricant
A change of state from liquid to solid is known as fusion. For instance, liquid nitrogen (N2) is turned into a solid by putting it in a sealed chamber with high pressure.
The Change of State from Liquid to Vapour
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If the heat is still supplied once all of the ice is converted to water, we will observe a rise in temperature till 1000C of temperature is reached. After that, the heat that is supplied to water is used in the transition of water into a vapor state. Hence, the change of state from liquid to gaseous/vapor state is known as vaporization.
At boiling point, water transforms from a liquid to a vapor state through the process of evaporation
Here also, until all the liquid is converted to a vapor state, the temperature of the system remains constant. Hence, the temperature at which both the gaseous and liquid state of the substance coexist in thermal equilibrium is known as the boiling point of the substance.
The process of condensation and evaporation
At standard pressure, the boiling point of a substance is known as its normal boiling point. With increasing pressure, the boiling point of a substance also increases and more heat will be required to convert the liquid into a vapor state. Similarly, as the pressure decreases, the boiling point of a substance is also reduced.
This is why, cooking is a bit difficult in hilly areas as the atmospheric pressure is lower on high altitudes, which lowers the boiling point of water. Therefore, a pressure cooker is used to increase the boiling point, thereby making the process of cooking fast.
Triple Point: The pressure and temperature at which the three curves, the vaporization curve, the fusion curve, and the sublimation curve meets so that all the three phases of a substance exist together is known as the triple point of the substance. For instance, the triple point of water exists at a temperature of 273.16 K and a pressure of 6.11 x 10–3 Pa.
Triple Point of Water
Read More: Unit of Heat
Phases of Matter
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Phases refer to the form of matter. Solid, liquid, and gas (vapor) are the three fundamental phases of matter, however other phases such as crystalline, colloid, glassy, amorphous, and plasma also exist. A phase change occurs when a matter of phase in one form transforms into a different form.
Phases of Matter
Not all substances pass through the three states sequentially: solid, liquid, gas. For instance, dry ice directly goes from a solid to a gaseous state through the process of sublimation. Here both solid and gaseous states coexist.
There are various processes involved in the phase change of matter known as deposition, condensation, vaporization, boiling, melting, solidification, and sublimation. A graph plotted between the Temperature and Pressure of a substance is known as a P-T diagram or a phase diagram.
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Applications of Change of State
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- The frost on the leaves on a winter morning is a result of the water vapor in the air transitioning into a solid when it comes in contact with the leaves.
- Melting of an Ice Cube.
- Steam rising on boiling of water.
- A glass of ice water when put at room temperature forms water droplets on the outer side of the glass as the vapor condenses into water.
Things to Remember
- The matter might change states when it absorbs or releases energy.
- These changes do not involve any change or alteration in the chemical properties of the substance involved.
- The change of state of a substance from solid to liquid is known as melting.
- The temperature at which both these states coexist is known as its melting point.
- The change of state from liquid to gaseous/vapor state is known as vaporization.
- Cooking is difficult in hilly areas as the atmospheric pressure is lower on high altitudes, which lowers the boiling point of water.
- When the pressure around a substance is increased, the freezing point also increases.
- Sublimation is the process of change of state of a substance from solid to vapor directly without going through the liquid state too.
- Phases refer to the form of matter.
- Solid, liquid, and gas (vapor) are the three fundamental phases of matter, however other phases such as crystalline, colloid, glassy, amorphous, and plasma also exist.
Read More: Specific Heat Capacity
Previous Year Questions
- Calculate the latent heat of ice. [JEE Main 2019]
- Temperature at the interface of two materials. [JEE Main 2019]
- Temperature at the boundaries of the insulating blocks. [VITEEE 2019]
- Determine the amount of water in the calorimeter. [JEE Main 2013]
- Temperature of a body on cooling in a given time. [JEE Main 2018]
- Determine temperature rise when coefficient of linear expansion is given. [JEE Main 2017]
- Calculate the specific heat of the liquid in a closed vessel. [JEE Main 2013]
- Determine percentage increment in water temperature. [JEE Main 2019]
- Temperature at which the clock will show correct time. [JEE Main 2016]
- Linear Expansion in Steel scale. [TS EAMCET 207]
- Expansion of a thermocol box of ice. [TS EAMCET 2017]
- Determine the volume increase of wooden box. [JEE Main 2021]
- Calculate rate of heat flow when dimensions are doubled. [JEE Advanced 2001]
- Level of water when ice melts in a jar. [KEAM 2004]
- Coefficient of Volume Expansion of water. [NEET 2013]
- Cubical to superficial expansion ratio. [NEET 2002]
- Linear expansion in steel rail. [JEE Main 2017]
Sample Questions
Ques. What refers to a change of state? (1 mark)
Ans. Matter usually exists in three states which are solids, liquids, and gases. The change of the substance from one state to another is termed a change of state.
Ques. What is the reason behind water boiling at low temperatures at High elevations? (2 marks)
Ans. Water boils at low temperatures at high elevations as the atmospheric pressure is lower at higher altitudes. This leads to difficulty in cooking at higher altitudes. Therefore, a pressure cooker is used for cooking in hilly areas as it increases the pressure, which further increases the boiling point of water and makes cooking easier.
Ques. What is condensation? What will happen to the temperature of the air surrounding the glass when condensation forms on a glass of ice water? (2 marks)
Ans. Condensation is the transition from the gaseous to the liquid state of materials. It's the polar opposite of vaporization. Atoms and molecules form clusters during condensation. The clusters eventually grow large enough to produce droplets. When water vapor (in its gaseous form) in the air comes into contact with a colder surface, condensation happens. For instance, a steamy mirror, morning dew in the sky, fog in the air
When condensation occurs on a glass of ice water, the temperature of the air surrounding the glass increases.
Ques. Explain the change of state that takes place in the process of melting. (2 marks)
Ans. Melting refers to the process of change of a substance from a solid into a liquid state. When heat is supplied to a solid, the motion of its molecules speeds up which in turn helps them overcome their force of attraction so that the molecules transform into a liquid.
Ques. What are the three states of matter? (3 marks)
Ans. The three states of matter are solid, liquid and gases. They can be further understood as:
- Solid: A solid is a state of matter in which particles are grouped in such a way that their shape and volume remain relatively steady. The atoms or molecules of a solid are securely bonded via chemical bonds, which gives it a rigid form.
- Liquid: A fluid with the consistency of water or oil that flows freely but has a consistent volume.
- Gas: A state (such as air) that does not have its own shape or volume but expands indefinitely.
Ques. Explain the process of vaporization. Give examples of the same. (3 marks)
Ans. The process of vaporization occurs when a liquid transforms into a gas. When you boil water, you can observe the vaporization process. Evaporation and boiling are the two methods of vaporization. The rapid vaporization of a liquid is known as boiling, and the steam that comes out of a boiling kettle is actually visible water vapor. With the help of vaporization, the salt is extracted from seawater.
Ques. If 5 J is the latent heat of ice melting, what is the heat of transition from 0oC ice to 15oC water, if 12 J is the heat of transition from 0oC water to 15oC water? (2 marks)
Ans. Heat of transition from 0oC ice to 15oC water= 12 + 5 = 17 J.
Ques. What mainly determines or leads to a change of state in a substance? (2 marks)
Ans. The change of state in a substance is mainly due to either:
- Temperature
- Pressure
Ques. How does a solid transform into a liquid? (2 marks)
Ans. The kinetic energy of the molecules of a solid substance increases as more and more heat is supplied to it, as a result of which these particles begin vibrating. As the particles vibrate with a higher frequency, they overcome the forces of attraction between them, getting detached from their original position. Hence, they are able to move more freely and transforms into a liquid state through the process of melting.
Ques. How does a liquid transition into a gas? (2 marks)
Ans. The molecules of a liquid move with a greater speed as more heat is supplied to it. Once it reaches a certain temperature, the particles gain enough energy to break away all the bonds or force of attraction between the liquid molecules. They undergo a phase change and transform into vapors through the process of evaporation.
Ques. What is sublimation? Give an example. (2 marks)
Ans. The process of a substance in a solid state to transform directly into vapor form without transitioning through the liquid state is known as sublimation.
For eg, dry ice changes directly from solid to vapor stage.
Ques. If the heat of transition from 0oC ice to 15oC water is 10 J, what is the heat of transition from 0oC ice to 15oC water? (2 marks)
Ans. Heat of transition = 10+15
= 25 J
Hence, the heat of transition required to transform 0oC ice to 15oC of water is 25 J.
Ques. What is deposition? (3 marks)
Ans. The deposition is a phase transition in which a gas becomes a solid without first passing through the liquid phase. When molecules settle out of a solution, this is called deposition.
Frost is the most common example of deposition. The deposition of water vapor on a solid surface caused by humid air or air containing water vapor is known as frost. When a surface, such as a leaf, is at a temperature below the freezing point of water and the surrounding air is humid, solid frost forms. Water vapor, for example, transforms immediately to ice in sub-freezing air without first becoming a liquid.
Ques. Why water in solid form is less dense than liquid water? (3 marks)
Ans. When water is frozen, the orientation of its hydrogen bonding is such that the molecules are pushed farther apart than in the case of liquid water and hence they take up more space. Hydrogen bonding is responsible for making ice less dense than liquid water.
Ques. Why the energy of sublimation of solid helium is lower than the energy of ice? (3 marks)
Ans. The atoms in solid helium are held by weaker Van der Waals forces. Hence, the energy required for sublimation is less while in the case of ice, its molecules have strong hydrogen bonds between them. For this reason, ice needs higher energy and higher temperatures to undergo the process of melting. Hence, ice has higher energy of sublimation than solid Helium.
Ques. Name the processes involved in the change of state. (5 marks)
Ans. The various processes involved are:
- Solidification, often known as freezing, is a phase shift in the liquid matter that produces a solid.
- A solid melts into a liquid when heated through the process of melting. This process occurs at a precise temperature known as the melting point.
- Condensation is the transition from the gaseous to the liquid state of materials.
- The process of vaporization occurs when a liquid transforms into a gas.
- Sublimation is the process of converting a solid to a gas without going through the liquid phase.
- The deposition is a phase transition in which a gas becomes a solid without first passing through the liquid phase.
- When a liquid is heated to its boiling point, it undergoes rapid evaporation.
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