NEET Important Questions States of Matter: Gases and Liquid

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States of Matter- Gases and Liquids- NEET

Gases are fluids that have no definite volume. Gases have no structure and take on the volume of the container in which they are contained. Compressing gases is possible. Temperature and pressure have an impact on them. The volume of gas in an enclosed container equals the container's volume. The same mass of gas can be contained in two containers of differing sizes.

Dry gases condense at very high pressures and very low temperatures, whereas vapours can condense at normal atmospheric pressures and temperatures. For example, at a typical atmospheric pressure of 14.7 pounds per square inch absolute (psia), water boils at 212 degrees Fahrenheit (100 degrees Celsius) and turns into steam at 212 degrees Fahrenheit. At a temperature of 70oF, however, the moisture content of air is water vapour (steam). Dalton's law of partial pressures is used to explain this later.

Liquids are fluids that have a distinct volume that is independent of the container's shape and volume. When a liquid is placed in a container, it takes on the shape of the container but maintains the same volume and mass at constant temperature and pressure. Non-compressible liquids are those that cannot be compressed. Under pressure, the volume will not vary considerably. At different temperatures, the volume of the liquid might alter significantly. The mercury thermometer makes use of this characteristic.

A free-standing surface is formed when a liquid is exposed to air pressure. All of the locations on the liquid's top surface are at the same level. "Sea-level," for example, is the common level of all connected seas and oceans. This is where land levels, or "altitudes," are measured.

Topics of States of Matter: Gases and Liquid

1. Three States of Matter: Solids are defined by their distinct shape and volume, with closely packed particles that vibrate in place. Liquids, however, conform to the shape of their container and possess a fixed volume, with particles that move more freely. Gases, the third state, exhibit neither a fixed shape nor volume, featuring widely spaced particles that move rapidly in all directions. This understanding of solid, liquid, and gas states is pivotal for grasping a wide array of chemical processes and phenomena, as it provides the foundation for explaining how substances behave under different conditions.

2. Intermolecular interactions: In gases, the molecules have weak forces between them, allowing them to move freely and independently. In liquids, these forces are slightly stronger, resulting in a more ordered but still fluid structure. Different substances exhibit varying types and strengths of intermolecular interactions, which influence their physical properties like boiling points and viscosity. Understanding these forces is essential in the study of gases and liquids, as they explain why some substances stay gaseous at room temperature while others become liquids, and how they respond to changes in temperature and pressure.

3. Types of bonding: In the world of gases and liquids, different types of bonding contribute to the properties and behavior of substances. Covalent bonding occurs when atoms share electrons, creating a strong connection. In ionic bonding, atoms transfer electrons, leading to the attraction between oppositely charged ions. Hydrogen bonding is a special form of covalent bonding where hydrogen atoms are attracted to highly electronegative elements, like oxygen or nitrogen. Van der Waals forces encompass various weak attractions between molecules, such as dipole-dipole interactions and dispersion forces. The nature and strength of these bonds determine properties like boiling points, solubility, and fluidity in gases and liquids.

4. Melting and boiling points: Melting and boiling points are crucial properties in the study of gases and liquids. The melting point is the temperature at which a substance changes from a solid to a liquid. It happens when the intermolecular forces between particles are overcome, allowing them to move and slide past each other.

The boiling point, on the other hand, is the temperature at which a liquid turns into a gas. At this point, the substance's vapor pressure equals the external pressure, allowing it to boil. 

Both melting and boiling points are influenced by intermolecular forces. Substances with stronger forces tend to have higher melting and boiling points, while those with weaker forces have lower points. 

5. Role of gas laws of elucidating the concept of the molecules: Gas laws are essential tools for understanding molecules in gases. They reveal how factors like volume, pressure, temperature, and quantity of gas molecules are related. These laws, including Boyle's, Charles's, and Avogadro's, describe the behavior of ideal gases under different conditions. By studying how real gases differ from ideal ones, we gain insights into molecular interactions. Gas laws are like a toolkit scientists use to explore the behavior of gas molecules in different states of matter.

6. Boyle's, Charles's, and Avogadro's, Gay Lussac's law: Boyle's law, Charles's law, Avogadro's law, and Gay-Lussac's law are fundamental gas laws that help us understand the behavior of gases.

1. Boyle's Law: It states that the pressure and volume of a gas are inversely proportional at constant temperature. When you decrease the volume of a gas, its pressure increases, and vice versa.

2. Charles's Law: This law explains that the volume and temperature of a gas are directly proportional at constant pressure. When you raise the temperature of a gas, its volume expands, and if you lower the temperature, the volume decreases.

3. Avogadro's Law: It tells us that the volume of a gas is directly proportional to the number of moles (quantity) of the gas, provided pressure and temperature remain constant.

4. Gay-Lussac's Law: This law relates the pressure and temperature of a gas when the volume is held constant. It shows that as you increase the temperature, the pressure of the gas also increases.

7. Ideal behavior of gases: The ideal behavior of gases is a concept that simplifies our understanding of how gases behave. It assumes that gas molecules are like tiny, perfectly elastic balls that don't take up any space themselves.

In ideal gas behavior:

• No Molecular Volume: The volume occupied by gas molecules is considered negligible compared to the volume of the container.

• No Intermolecular Forces: Ideal gases assume that there are no attractive or repulsive forces between gas molecules.

• Random Motion: Gas molecules move randomly in all directions and only interact through collisions.

• Constant Kinetic Energy: The average kinetic energy of gas molecules is directly proportional to the temperature in Kelvin.

While no real gas is perfectly ideal, this concept provides a useful starting point for understanding gas behavior, especially at low pressures and high temperatures.

8. Empirical derivation of the gas equation: The empirical derivation of the gas equation for ideal gases simplifies the relationship between pressure (P), volume (V), and temperature (T) in a way that makes it easier to understand. This empirical derivation led to the ideal gas law.

Imagine a gas confined in a container. When you increase the pressure (P) on the gas, it compresses and occupies less space (V). If you increase the temperature (T), the gas expands and takes up more space. So, the gas's behavior can be described by a simple equation:

$PV = nRT$

• P is pressure.

• V is volume.

• n is the number of moles of gas

• R is the universal gas constant.

• T is the absolute temperature.

9. Avogadro number: The Avogadro number is a fundamental constant in chemistry. It represents the number of atoms, ions, or molecules in one mole of a substance, which is approximately $6.022 \times 10^23$. This number helps scientists count and understand the incredibly small particles at the atomic and molecular level, making it essential for various chemical calculations.

10. Ideal gas equation: The ideal gas equation, known as the ideal gas law, relates pressure (P), volume (V), temperature (T), and the number of gas molecules (n). It's written as $PV = nRT$. This equation helps determine the number of gas molecules when you know the other variables. It's a fundamental concept in understanding how gases behave under various conditions. However, it's important to remember that it's an approximation that works best for ideal gases under specific conditions, and real gases may deviate from this behavior under extreme conditions.

11. Kinetic energy and molecular speeds: Kinetic energy refers to the energy of motion. In gases and liquids, the molecules are constantly moving. The kinetic energy of these molecules is directly related to their speed. When molecules move faster, they have higher kinetic energy.

Molecular speed means how fast these tiny particles move within a substance. In gases, molecules move rapidly and randomly in all directions. In liquids, they move less freely than in gases but still have considerable speed.

12. Deviation from ideal behavior: In gases and liquids, deviations from ideal behavior occur due to molecular interactions. In high-pressure and low-temperature conditions, these interactions become significant, causing deviations from ideal gas laws.

13. Liquefaction of gases: The liquefaction of gases is a process where gases are cooled and compressed to transform them into liquids. This process is essential for various applications, such as the production of industrial and medical gases. It involves lowering the temperature and increasing the pressure of the gas until its particles slow down and come closer together, turning it into a liquid. Liquidified gases are easier to transport and store, making them more practical for many purposes. This process is vital for ensuring a stable and efficient supply of gases that are used in industries, hospitals, and various other fields.

14. Critical Temperature: The critical temperature is a specific temperature for each substance above which it's impossible to liquefy the gas, no matter how much pressure is applied. It's like a point of no return for gases. When a gas is heated beyond its critical temperature, even extremely high pressure won't make it turn into a liquid. This critical temperature varies for different gases and is a crucial property when it comes to understanding their behavior under different conditions. For some gases, like carbon dioxide, the critical temperature is relatively low, which is why you might have seen dry ice (frozen carbon dioxide) even at room temperature.

15. Vapor pressure: Vapor pressure is the pressure exerted by the vapor (gaseous form) of a substance in equilibrium with its liquid or solid form. Imagine a closed container with a liquid in it. Some liquid molecules escape from the surface and turn into vapor. As more and more molecules do this, they create pressure. Vapor pressure increases with temperature because higher temperatures make the molecules move faster and escape from the liquid more easily. When the vapor pressure equals the external pressure (like the atmospheric pressure), the liquid starts to boil.

16. Viscosity and surface tension: 

Viscosity: Imagine trying to stir a thick, gooey substance like honey with a spoon. It resists your efforts and flows slowly. That's viscosity, the measure of a liquid's resistance to flow. Honey has high viscosity, while water has low viscosity. Viscosity depends on the liquid's internal friction and is essential to understand fluid behavior in everything from car engines to the human body.

Surface Tension: Have you ever seen a water droplet on a leaf? Its round shape is due to surface tension. Surface tension is like an invisible "skin" on the surface of a liquid that makes it act like a stretched rubber sheet. This property helps insects like water striders walk on water. The stronger the surface tension, the more rounded the droplets, which is why it beads up on a surface.

Characteristics of States of Matter - Gases and Liquid- NEET

Gases have the following characteristics: 

• They have no defined shape or volume. They expand to the size of the container in which they are contained.

• Gases are fluid and have an easy flow.

• Unless compressed, gases have a low density. Gases are particularly compressible because they are made up of microscopic particles in a big, open environment.

• Gases disperse and effuse (mix and spread out) (travel through small holes).

The following qualities can be found in all liquids:

• Liquids are almost impervious to compression. Liquid molecules are very close to one another. There isn't a lot of room between the molecules. It is impossible to force the molecules closer together.

• Liquids have a constant volume but no constant shape.

• They have a constant volume but no fixed or distinct shape. If you pour 100 mL of water into a cup, the water will take on the shape of the cup. Pour the liquid from the cup into the bottle; the liquid has changed shape and now resembles a bottle.

• Liquids flow from one level to the next.

• Under typical circumstances, liquids have boiling points higher than room temperature. When liquids are heated, they gradually transition to a vapour or gaseous state. This procedure is called boiling.

NEET 2025 Exam Pattern

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NEET 2025 Chemistry: Chapter- Wise Weightage

The following table shows the different chapters students need to prepare for the NEET 2025 Chemistry exam along with the weightage of each chapter.

Conclusion

Vedantu’s NEET 2025 Important questions for the topic ‘States of Matter: Liquid And Gas will help students revise the chapter with the best study materials. The important questions with solutions that have been provided in the PDF are prepared by our subject matter experts after extensive research. It is recommended that students go through these important questions after understanding the concepts covered in the NCERT Chemistry textbook, as this helps them to understand the questions with ease. Also, this ensures efficiency in answering the questions on their own during the exam.

NEET Chemistry Important Questions - Chapter Pages