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States of matter- Part 2

Punam Bagad
Punam Bagad

Latent heat is the energy absorbed or released during a phase change of matter at a constant temperature. There are different types of latent heat including latent heat of fusion and latent heat of vaporization. Latent heat of fusion is the energy required to change a substance from a solid to a liquid or vice versa, while latent heat of vaporization is the energy required to change a substance from a liquid to a gas. The amount of latent heat depends on the specific substance and temperature. Vapour pressure is the pressure exerted by the vapors of a liquid or solution and varies with temperature, intermolecular forces, and surface area. Adding a non-volatile solute decreases the vapour pressure of the solvent.

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STATES OF MATTER & PROPERTIES OF MATTER Ms. Punam Dilip Bagad Assistant Professor, Dept. of Pharmaceutics GESs Sir Dr. M. S. Gosavi College of Pharm. Edu. & Research, Nashik-422005, INDIA 1
Latent Heat The term was introduced around 1762 by British chemist Joseph Black. It is derived from the Latin latere (to lie hidden). Heat is an important component of phase changes. As you apply heat to the water, the temperature of the water increases until it reaches 100 属C, the boiling point of water. The water will stay at this temperature until all of the water changes from liquid to a gas. During this process, you are continuing to add heat energy to the water, but the water temperature does not increase. 2
Latent Heat Normally when heat energy is added to or removed from an object, the temperature of the object changes; however, during phase changes, the temperature of an object stays constant. The temperature remains the same because energy is required for an object to change phases. Latent heat is the heat energy per mass unit required for a phase change to occur. OR Latent heat (hidden heat) is defined as the total energy absorbed or released when a substance change its physical state completely at a constant temperature. 3
Latent Heat Specific latent heat: A specific latent heat expresses the amount of energy in the form of heat required to completely effect a phase change of a unit of mass, usually 1 kg of a substance. The formula for latent heat is: Q = This equation relates the heat Q that must be added or removed for an object of mass m to change phases. The object's individual latent heat is noted by L. The unit of latent heat is J/kg The values of latent heat are variable depending on the nature of the phase change taking place. 4
TYPES OF Latent Heat The change of one phase to another phase of matter happens at a specific temperature and pressure. The change happens with the absorption or release of heat followed by a change in the volume and density of the substance. 1. Latent heat of fusion (Lf) 2. Latent heat of Vaporization (Lv) 5
TYPES OF Latent Heat Sr. No. Term used for phase change Description of phase change 1 Fusion/Melting Solid to liquid 2 Freezing Liquid to solid 3 Vaporization/Boiling Liquid to gas 4 Condensation Gas to liquid 5 Sublimation Solid to gas 6 Deposition Gas to solid 7 Evaporation Liquid to gas 6
TYPES OF Latent Heat Latent heat of fusion (Lf): The energy needed to break the bond in a solid and change it into a liquid. It is the heat absorbed by melting solid. For Ice at 0 属C you would need 80 calories to melt each gram of ice. Solid water (ice) melts at 0 属C. If an ice cube is heated, it will begin to melt. The interesting thing is that its temperature is kept constant in this process: Even though heat is being supplied! That is because heat energy is being used to overcome the intermolecular forces which keep the water molecules together in a lattice. 7
TYPES OF Latent Heat Latent heat of fusion (Lf): Different materials will take different amounts of energy to melt. This is called the latent heat of fusion. It is the energy required to transform a solid substance (already heated to its melting point) into a liquid. 8
TYPES OF Latent Heat Latent heat of Vaporization (Lv): It is the energy needed to break the bond in a liquid and change it to a gas. It is the heat absorbed during boiling and for ice it is 540 calories per gram. When water boils, it does so at a constant temperature. The heat in this case is also used to overcome intermolecular forces that are present 9
Numericals Q. 1: Calculate the amount of heat added to 1 gram gold to change phase from solid to liquid. The heat of fusion for gold is 64.5*103J/Kg. Q. 2: Determine the amount of heat absorbed by 1 kg water to change phase from liquid to vapor. Heat of vaporization for water = 2256*103J/Kg. 10
Vapour pressure Vapour pressure of liquid solutions is defined as the pressure exerted by the vapors on of a liquid in its equilibrium state with the pure liquid at a given temperature. Liquid Solution is formed when we dissolve a solid, liquid or gas in a particular liquid solvent. It varies with the nature of liquid and temperature of the surroundings. Some characteristics of the vapour pressure of liquid solutions are as follows: 11
Vapour pressure The pure liquid has more vapour pressure as compared to liquids solution. Example: Take two beakers, one filled with water and other with lemon juice and water, you will find that the beaker filled with water has more vapour pressure Vapour pressure is inversely proportional to forces of attraction between molecules of a liquid. Vapour pressure increases with increase in temperature, as molecules gain kinetic energy and vaporise quickly. 12
Vapour pressure Liquid solution can contain volatile solute and solvent as well. In most cases, the solvent is volatile in nature and the solute left out to be non-volatile. Vapour pressure can be evaluated in two cases which are: Vapour pressure of liquid-liquid solutions that is, solute and solvent both are in liquid phase Vapour pressure of solid-liquid solutions that is, solute is in solid state and solvent is in liquid phase. 13
Vapour pressure Vapour Pressure of Solutions of Solids in Liquids: Another type of solutions is solids in liquid solution, in which we take solid as the solute and liquid as the solvent. For example, when we dissolve glucose, sugar or salt in water, we get solids in liquids type of solution. Generally, the solute is non-volatile in nature and the vapour pressure is less than the pure vapour pressure of the solution. 14
Vapour pressure The decrease in vapour pressure is due to: As evaporation is a surface phenomenon, the more the surface, the greater the evaporation and hence more the vapour pressure. In a pure liquid, there is more surface area available for the molecules to vapourise, thereby have more vapour pressure. On the other hand, when we add a non-volatile solute, the solvent molecules get less surface to escape and hence experience low vapour pressure The number of molecules evaporating or leaving the surface is much greater in pure liquid solutions to that of non-volatile solute in solvent. 15
Vapour pressure 16
Vapour pressure Factors affecting Vapor pressure a) Temperature Temperature has the most significant impact on the vapor pressure as with higher temperature, the energy of molecules rises and there is an increase in their ability to escape. A lower temperature, on the other hand, makes it difficult for the molecules to escape from the liquid. b) Molecule Type The intermolecular force and the vapor pressure are inversely related to each other. When the intermolecular force between the molecules is strong, the vapor pressure will be low. However, if the intermolecular force is weak, the vapor pressure is likely to be higher. 17
Vapour pressure Factors affecting Vapor pressure c) Surface Area As against the other factors, the surface area of the solid or liquid will have no impact on the vapor pressure. In other words, it will hardly matter whether you use a larger surface area or a smaller surface area, the vapor pressure will still be the same with constant molecule type and temperature. 18

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States of matter- Part 2

  • 1. STATES OF MATTER & PROPERTIES OF MATTER Ms. Punam Dilip Bagad Assistant Professor, Dept. of Pharmaceutics GESs Sir Dr. M. S. Gosavi College of Pharm. Edu. & Research, Nashik-422005, INDIA 1
  • 2. Latent Heat The term was introduced around 1762 by British chemist Joseph Black. It is derived from the Latin latere (to lie hidden). Heat is an important component of phase changes. As you apply heat to the water, the temperature of the water increases until it reaches 100 属C, the boiling point of water. The water will stay at this temperature until all of the water changes from liquid to a gas. During this process, you are continuing to add heat energy to the water, but the water temperature does not increase. 2
  • 3. Latent Heat Normally when heat energy is added to or removed from an object, the temperature of the object changes; however, during phase changes, the temperature of an object stays constant. The temperature remains the same because energy is required for an object to change phases. Latent heat is the heat energy per mass unit required for a phase change to occur. OR Latent heat (hidden heat) is defined as the total energy absorbed or released when a substance change its physical state completely at a constant temperature. 3
  • 4. Latent Heat Specific latent heat: A specific latent heat expresses the amount of energy in the form of heat required to completely effect a phase change of a unit of mass, usually 1 kg of a substance. The formula for latent heat is: Q = This equation relates the heat Q that must be added or removed for an object of mass m to change phases. The object's individual latent heat is noted by L. The unit of latent heat is J/kg The values of latent heat are variable depending on the nature of the phase change taking place. 4
  • 5. TYPES OF Latent Heat The change of one phase to another phase of matter happens at a specific temperature and pressure. The change happens with the absorption or release of heat followed by a change in the volume and density of the substance. 1. Latent heat of fusion (Lf) 2. Latent heat of Vaporization (Lv) 5
  • 6. TYPES OF Latent Heat Sr. No. Term used for phase change Description of phase change 1 Fusion/Melting Solid to liquid 2 Freezing Liquid to solid 3 Vaporization/Boiling Liquid to gas 4 Condensation Gas to liquid 5 Sublimation Solid to gas 6 Deposition Gas to solid 7 Evaporation Liquid to gas 6
  • 7. TYPES OF Latent Heat Latent heat of fusion (Lf): The energy needed to break the bond in a solid and change it into a liquid. It is the heat absorbed by melting solid. For Ice at 0 属C you would need 80 calories to melt each gram of ice. Solid water (ice) melts at 0 属C. If an ice cube is heated, it will begin to melt. The interesting thing is that its temperature is kept constant in this process: Even though heat is being supplied! That is because heat energy is being used to overcome the intermolecular forces which keep the water molecules together in a lattice. 7
  • 8. TYPES OF Latent Heat Latent heat of fusion (Lf): Different materials will take different amounts of energy to melt. This is called the latent heat of fusion. It is the energy required to transform a solid substance (already heated to its melting point) into a liquid. 8
  • 9. TYPES OF Latent Heat Latent heat of Vaporization (Lv): It is the energy needed to break the bond in a liquid and change it to a gas. It is the heat absorbed during boiling and for ice it is 540 calories per gram. When water boils, it does so at a constant temperature. The heat in this case is also used to overcome intermolecular forces that are present 9
  • 10. Numericals Q. 1: Calculate the amount of heat added to 1 gram gold to change phase from solid to liquid. The heat of fusion for gold is 64.5*103J/Kg. Q. 2: Determine the amount of heat absorbed by 1 kg water to change phase from liquid to vapor. Heat of vaporization for water = 2256*103J/Kg. 10
  • 11. Vapour pressure Vapour pressure of liquid solutions is defined as the pressure exerted by the vapors on of a liquid in its equilibrium state with the pure liquid at a given temperature. Liquid Solution is formed when we dissolve a solid, liquid or gas in a particular liquid solvent. It varies with the nature of liquid and temperature of the surroundings. Some characteristics of the vapour pressure of liquid solutions are as follows: 11
  • 12. Vapour pressure The pure liquid has more vapour pressure as compared to liquids solution. Example: Take two beakers, one filled with water and other with lemon juice and water, you will find that the beaker filled with water has more vapour pressure Vapour pressure is inversely proportional to forces of attraction between molecules of a liquid. Vapour pressure increases with increase in temperature, as molecules gain kinetic energy and vaporise quickly. 12
  • 13. Vapour pressure Liquid solution can contain volatile solute and solvent as well. In most cases, the solvent is volatile in nature and the solute left out to be non-volatile. Vapour pressure can be evaluated in two cases which are: Vapour pressure of liquid-liquid solutions that is, solute and solvent both are in liquid phase Vapour pressure of solid-liquid solutions that is, solute is in solid state and solvent is in liquid phase. 13
  • 14. Vapour pressure Vapour Pressure of Solutions of Solids in Liquids: Another type of solutions is solids in liquid solution, in which we take solid as the solute and liquid as the solvent. For example, when we dissolve glucose, sugar or salt in water, we get solids in liquids type of solution. Generally, the solute is non-volatile in nature and the vapour pressure is less than the pure vapour pressure of the solution. 14
  • 15. Vapour pressure The decrease in vapour pressure is due to: As evaporation is a surface phenomenon, the more the surface, the greater the evaporation and hence more the vapour pressure. In a pure liquid, there is more surface area available for the molecules to vapourise, thereby have more vapour pressure. On the other hand, when we add a non-volatile solute, the solvent molecules get less surface to escape and hence experience low vapour pressure The number of molecules evaporating or leaving the surface is much greater in pure liquid solutions to that of non-volatile solute in solvent. 15
  • 17. Vapour pressure Factors affecting Vapor pressure a) Temperature Temperature has the most significant impact on the vapor pressure as with higher temperature, the energy of molecules rises and there is an increase in their ability to escape. A lower temperature, on the other hand, makes it difficult for the molecules to escape from the liquid. b) Molecule Type The intermolecular force and the vapor pressure are inversely related to each other. When the intermolecular force between the molecules is strong, the vapor pressure will be low. However, if the intermolecular force is weak, the vapor pressure is likely to be higher. 17
  • 18. Vapour pressure Factors affecting Vapor pressure c) Surface Area As against the other factors, the surface area of the solid or liquid will have no impact on the vapor pressure. In other words, it will hardly matter whether you use a larger surface area or a smaller surface area, the vapor pressure will still be the same with constant molecule type and temperature. 18