Change of State and Evaporation Questions in English

(N/A) Steam at $373 K$ $(100^{\circ} C)$ contains more energy than boiling water at the same temperature because it possesses additional latent heat of vaporisation.
$(b)$ $A$ saucer has a larger surface area than a cup. Since evaporation is a surface phenomenon,a larger surface area increases the rate of evaporation,leading to faster cooling of the tea.
$(c)$ An earthen pot has numerous microscopic pores. Water continuously evaporates through these pores. The energy required for this evaporation is absorbed from the remaining water inside the pot,causing the water to cool down.

(N/A) The water vapour present in the air,upon coming in contact with the cold surface of the glass tumbler,loses energy,gets condensed,and converts into liquid water droplets.
$(b)$ Cotton is a good absorber of water. It absorbs sweat from our body and exposes it to the atmosphere for easy evaporation. This process of evaporation causes a cooling effect on our skin.
$(c)$ The sprinkled water evaporates by absorbing a large amount of latent heat of vaporisation from the roof or open ground and the surrounding air,which results in the cooling of the area.

(N/A) Surface area: As the surface area increases,more particles are exposed to the surface,leading to a higher rate of evaporation.
$(b)$ Temperature: With an increase in temperature,the kinetic energy of the liquid particles increases,allowing more particles to escape into the vapor state,thus increasing the rate of evaporation.
$(c)$ Humidity: Humidity refers to the amount of water vapor present in the air. As humidity increases,the air becomes saturated,which decreases the rate of evaporation.

(N/A) The state of matter obtained is solid.
$(b)$ The process is called sublimation. Sublimation is defined as the phase transition in which a substance changes directly from a solid state to a gaseous state or vice-versa without passing through the liquid state.
$(c)$ The common name of the product obtained is dry ice.

(N/A) During a change of state,the heat energy supplied increases the kinetic energy $(KE)$ of the particles,which helps them overcome the intermolecular forces of attraction. This leads to a change in the arrangement of particles,causing the matter to transition from one state to another (e.g.,solid to liquid).
$(b)$ When a solid melts,the temperature remains constant because the heat energy supplied is entirely consumed as latent heat of fusion. This energy is used to overcome the strong intermolecular forces of attraction holding the solid particles together,rather than increasing the kinetic energy of the particles.

(N/A) The temperature at which a solid melts to become a liquid at atmospheric pressure is called its melting point.
$(b)$ Ice melts at $273.16 K$ (or $273 K$).
$(c)$ The temperature does not rise because the heat supplied is used up in changing the state of the substance by overcoming the forces of attraction between the particles.
$(d)$ This heat energy is known as the latent heat of fusion.

(N/A) Gases have large interparticle spaces and no fixed shape or volume,which justifies that $CO_2$ is a gas.
$(b)$ $A$ gas can be liquefied by increasing the pressure and decreasing the temperature,which brings the particles closer together.
$(c)$ Solid $CO_2$ is called dry ice because it undergoes sublimation,meaning it converts directly from a solid state to a gaseous state without passing through the liquid phase.
$(d) (i)$ $CNG$: Compressed Natural Gas.
$(ii)$ $LPG$: Liquefied Petroleum Gas.

(N/A) During evaporation,a small fraction of particles at the surface having higher $KE$ (Kinetic Energy) is able to break away from the force of attraction of other particles and gets converted into vapour.
$(b)$ $(i)$ Rate of evaporation increases with temperature because an increase in temperature provides more $KE$ to the particles,allowing more particles to escape the surface.
$(ii)$ Rate of evaporation increases with wind speed because the moving air carries away the water vapour particles,thereby decreasing the concentration of water vapour in the surrounding area.
$(iii)$ Rate of evaporation decreases with humidity because the air is already saturated with water vapour,leaving less space for additional water molecules to evaporate.

(N/A) Similarity: In both processes,a liquid is converted into vapours.
Difference: Evaporation is a surface phenomenon,whereas boiling is a bulk phenomenon.
$(b)$ $(i)$ Cotton is a good absorber of water. It absorbs perspiration from our body and exposes it to the atmosphere for evaporation,which causes a cooling effect.
$(ii)$ $A$ wet handkerchief placed on the forehead absorbs heat from the body as the water evaporates. This process of evaporation causes cooling,which helps in lowering the body temperature.
$(iii)$ During the rainy season,the humidity in the atmosphere is high. Since the air is already saturated with water vapours,the rate of evaporation decreases,causing wet clothes to dry slowly.

(A) Steam at $373 \, K$ will cause more severe burns.
This is because steam contains additional energy known as the latent heat of vaporization.
At $373 \, K$,water molecules in the steam state have absorbed extra heat to change their phase from liquid to gas.
When steam comes into contact with the skin,it releases this latent heat along with its thermal energy,resulting in more severe burns compared to water at the same temperature.

(B) To liquefy gases,the following two physical quantities must be altered:
$(i)$ Pressure is increased: Increasing pressure brings the gas particles closer together,which decreases the interparticle space.
$(ii)$ Temperature is reduced: Decreasing the temperature reduces the kinetic energy of the particles,which increases the interparticle forces of attraction,allowing the gas to condense into a liquid state.

(N/A) During the process of evaporation,the particles of the liquid absorb energy from the surroundings to overcome the force of attraction and change into the vapour state. This absorption of energy from the surroundings makes the surroundings cold.
$(b)$ An earthen pot has a large number of extremely small pores on its surface. Water continuously seeps out through these pores and evaporates. The energy required for this evaporation is taken from the remaining water inside the pot. As the heat is lost from the water,it cools down.

(N/A) The physical state of matter can be changed by increasing or decreasing the pressure applied to it.
For example,a gas can be liquefied by applying high pressure. This occurs because,under high pressure,the molecules of the gas are forced to come closer to each other,which increases the intermolecular forces of attraction,thereby converting the gas into a liquid state.

(N/A) Latent heat of fusion is the amount of energy required to change $1 \, kg$ of a solid into a liquid at its melting point.
During the process of melting ice,the heat supplied is used up in changing the state of the substance by overcoming the forces of attraction between the particles. Since this energy is consumed to break the intermolecular bonds rather than increasing the kinetic energy of the particles,the temperature does not rise and remains constant.

(N/A) Steam contains water particles that possess high kinetic energy due to the latent heat of vaporization. When steam comes in contact with the skin,it releases this extra heat energy,causing severe burns.
Conversely,in the case of ice,the water particles possess lower energy. When ice comes in contact with the skin,it absorbs heat energy from the surroundings (or the body) to undergo a phase change from solid to liquid,thereby producing a cooling effect.

(C) The interconversion of the states of matter can be achieved in the following two ways:
$(i)$ By changing the temperature: Increasing or decreasing the temperature can cause a substance to change its state (e.g.,melting of ice into water or freezing of water into ice).
$(ii)$ By changing the pressure: Increasing or decreasing the pressure can also change the state of matter,especially in gases (e.g.,liquefaction of gases by applying high pressure and lowering the temperature).

(N/A) The melting point is defined as the temperature at which a solid substance changes its state from solid to liquid at atmospheric pressure.
Fusion is the physical process of a substance changing from a solid state to a liquid state.
In scientific terminology,melting and fusion refer to the exact same process of phase transition from solid to liquid.

(N/A) During the change of state,the heat energy supplied is used up in overcoming the force of attraction between the particles of the substance. This energy is known as latent heat. Since this energy does not increase the kinetic energy of the particles,the temperature of the substance remains constant during the phase transition.

(N/A) Evaporation is the phenomenon of the change of a liquid into vapours at any temperature below its boiling point.

Evaporation	Boiling
$1.$ Evaporation occurs on its own at all temperatures.	$1.$ Boiling occurs at a particular temperature when the liquid is heated.
$2.$ Evaporation is a surface phenomenon,i.e.,it takes place only from the surface of the liquid.	$2.$ Boiling is a bulk phenomenon,i.e.,it involves the formation of vapours from the entire liquid.
$3.$ Evaporation causes a cooling effect.	$3.$ Boiling does not cause any cooling effect.

(B) Evaporation is a process in which liquid changes into vapor at any temperature below its boiling point.
This process occurs only at the surface of the liquid because the particles at the surface have higher kinetic energy than the particles in the bulk of the liquid,allowing them to overcome the forces of attraction and escape into the atmosphere.
Therefore,evaporation is considered a surface phenomenon.

(C) Evaporation is a surface phenomenon where particles at the surface of a liquid gain enough kinetic energy to overcome the forces of attraction and escape into the vapor state.
To overcome these intermolecular forces of attraction,the particles require energy.
This energy is taken from the surroundings or the liquid itself,which leads to a cooling effect.
Therefore,heat is absorbed during the process of evaporation.

(D) Boiling is a process in which a liquid changes into a gas at a constant temperature called the boiling point.
Unlike evaporation,which occurs only at the surface of a liquid,boiling occurs throughout the entire volume of the liquid.
Therefore,heat is supplied to the entire mass of the liquid,and bubbles of vapor form within the bulk of the liquid and rise to the surface.
Thus,boiling is considered a bulk phenomenon.

(B) Gases can be liquefied by applying high pressure and reducing the temperature.
Increasing the pressure brings the gas particles closer together,while decreasing the temperature reduces their kinetic energy,allowing intermolecular forces to hold the particles together in a liquid state.

(D) Evaporation is a surface phenomenon where liquid molecules at the surface gain enough kinetic energy to overcome the intermolecular forces and escape into the vapor phase.
Unlike boiling,which occurs at a specific boiling point throughout the bulk of the liquid,evaporation can occur at any temperature.
As the temperature increases,the rate of evaporation increases because more molecules possess sufficient kinetic energy to escape the surface.

(A) The process of water turning into ice is known as freezing or solidification. During this phase change,water molecules lose kinetic energy and transition from a liquid state to a solid state. According to the principles of thermodynamics,when a substance changes from a higher energy state (liquid) to a lower energy state (solid),it must release energy to the surroundings. Therefore,heat is evolved (released) during the solidification of water into ice.

(B) The boiling point of a liquid is defined as the fixed temperature at which the vapor pressure of the liquid becomes equal to the atmospheric pressure.
Under normal atmospheric pressure $(1 \text{ atm})$,every pure liquid boils at a specific,constant temperature known as its boiling point.
Therefore,boiling occurs at a fixed temperature under normal atmospheric pressure.

(D) Evaporation is a surface phenomenon where liquid molecules gain enough kinetic energy to escape into the vapor phase.
Factors that increase the rate of evaporation include:
$1$. Increase in surface area: More molecules are exposed to the surface.
$2$. Increase in temperature: Molecules gain higher kinetic energy,allowing more to escape.
$3$. Decrease in humidity: The air can hold more water vapor.
$4$. Increase in wind speed: Water vapor particles are moved away,creating space for more evaporation.
Therefore,an increase in the temperature of water increases the rate of evaporation.

(C) Sublimation is the process of transition of a substance directly from the solid to the gas phase or from the gas phase directly to the solid phase,without passing through the intermediate liquid state.
Option $A$ is incorrect because the conversion of solid to liquid is called melting or fusion.
Option $B$ is incorrect because the conversion of solid to vapour is called sublimation.
Option $C$ is correct as it describes the deposition process,which is a type of sublimation.
Option $D$ is incorrect because the conversion of vapour to solid is called deposition,not freezing.

(TRUE) The statement is True.
The relationship between the Celsius scale and the Kelvin scale is given by the formula: $T(K) = T(^{\circ}C) + 273.15$.
For standard calculations,we use the approximation $T(K) = T(^{\circ}C) + 273$.
Substituting $T(^{\circ}C) = -273$,we get $T(K) = -273 + 273 = 0 K$.
Therefore,$-273^{\circ} C$ is equivalent to absolute zero,which is $0 K$.

(TRUE) The statement is $True$.
In physics and chemistry,the term $vapor$ refers to a substance in the gas phase at a temperature lower than its critical temperature. This means that the substance can be condensed to a liquid or solid state by increasing the pressure on it without lowering the temperature. Substances like water,which are liquid at room temperature,exist as $vapor$ when they evaporate.

(B) The statement is False.
Latent heat is defined as the amount of heat energy absorbed or released by a substance during a change of state (e.g.,from solid to liquid or liquid to gas) without any change in its temperature.
It is called 'latent' (which means 'hidden') because this heat does not cause a rise in temperature and cannot be detected by a thermometer,nor can it be seen visually.

(TRUE) The statement is True.
Explanation:
$1$. Gases consist of particles that are far apart and move randomly at high speeds.
$2$. By applying high pressure,the distance between gas particles is reduced,bringing them closer together.
$3$. By reducing the temperature,the kinetic energy of the gas particles decreases,causing them to slow down.
$4$. When particles are brought close enough and their kinetic energy is sufficiently low,the intermolecular forces of attraction become strong enough to hold them together,resulting in the transition of the gas into a liquid state.

(N/A) $(i)$ The chemical composition of the substance remains unchanged during the process.
$(ii)$ No new chemical substance is formed; the identity of the matter remains the same.
$(iii)$ The change is often reversible,and the substance exhibits different physical properties (like shape or state) while maintaining its original chemical identity.

(C) Sublimation is the process where a solid directly changes into a gas without passing through the liquid state at atmospheric pressure.
To liquefy a substance that normally sublimes,we must increase the pressure on the substance.
By applying high pressure,the intermolecular forces become strong enough to maintain the liquid phase.
Therefore,substances that sublime can be made to liquefy by heating or compressing them under high pressure,which prevents them from transitioning directly to the gaseous state.

(D) Sublimation is the process in which a solid changes directly into a gas without passing through the liquid state.
Substances that exhibit this property are known as sublimable substances.
Iodine,camphor,ammonium chloride $(NH_4Cl)$,anthracene,and naphthalene are well-known examples of substances that sublime easily upon heating.
Petrol,acetone,kerosene,and diesel are liquids at room temperature and do not sublime.
Therefore,the correct group of substances is iodine,camphor,ammonium chloride,anthracene,and naphthalene.

(A) The physical state of matter (solid,liquid,or gas) is determined by the kinetic energy of its particles and the intermolecular forces of attraction.
To change the physical state,one must either increase the kinetic energy (by heating/supplying energy) to overcome intermolecular forces or decrease the kinetic energy (by cooling/removing energy) to allow particles to come closer.
Therefore,a change in physical state requires an exchange of energy with the surroundings,either by adding or removing it.

(N/A) The qualities possessed by Ram are:
$(i)$ Keen observation skills.
$(ii)$ Curiosity to learn from elders.
$(iii)$ Respectful and communicative relationship with his mother.
$(b)$ $A$ wet khus-khus screen keeps the room cool due to the process of evaporation. When the air passes through the wet screen,the water present in the khus-khus absorbs heat from the incoming air to undergo phase change (evaporation). As the air loses heat,its temperature decreases,resulting in a cooling effect inside the room.

(N/A) An earthen pot has small pores on its surface from which water evaporates continuously. The latent heat of vaporization required for the process of evaporation is taken from the remaining water inside the pot. As the heat is removed from the water,its temperature decreases,making the water cool during summers.
$(b)$ The qualities shown by Sameer are:
$(i)$ Respectful behavior towards elders.
$(ii)$ Curiosity and being a good observer.

(N/A) The qualities shown by Ravi are:
$(i)$ Presence of mind and in-depth knowledge.
$(ii)$ Caring and helpful nature.
$(iii)$ Being a true and responsible friend.
$(b)$ Steam at $373 \ K$ $(100^{\circ}C)$ causes more severe burns than boiling water at the same temperature. This is because the particles in steam possess extra energy in the form of latent heat of vaporisation,which is the amount of heat energy required to change $1 \ kg$ of liquid to gas at atmospheric pressure at its boiling point.

(N/A) Diffusion is the spontaneous movement of a substance from a region of higher concentration to a region of lower concentration. Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane.
$(i)$ Unicellular freshwater organisms,such as Amoeba,gain water through osmosis.
$(ii)$ Plant roots absorb water from the soil through osmosis.

(N/A) $(i)$ During melting,the temperature of the ice remains constant at $0^{\circ} C$. It starts rising only after all the ice has melted into water.
$(ii)$ At $100^{\circ} C$,water starts boiling and the temperature remains constant during the conversion of water into steam (latent heat of vaporization).