Chapter 5:- Heat
Chapter 2:- Periodic Classification of Element
Chapter 3:- Chemical Reaction and Equation
Chapter 4:- Effect of Electric Current
Chapter 6 Refraction of Light
Chapter 7:- Lenses
Chapter 8 :- Metallurgy
Chapter 9 Carbon Compound
Chapter 10 :- Space Mission
TextBook Soltuion of heat
1. Fill in the blanks and rewrite the sentence..
a. The amount of water vapour in air is determined in terms of its …………
Answer:_ Absolute Humidity
b. If objects of equal masses are given equal heat, their final temperature will be different. This is due to difference in their ………………
Answer:_ Different specific Heat Capacity
c. During transformation of liquid phase to solid phase, the latent heat is ………….
Answer:- Latent Heat of fusion
2. Observe the following graph.
Considering the change in volume of water as its temperature is raised from 0 oC, discuss the difference in the behaviour of water and other substances. What is this behaviour of water called?
Answer:_ This graph represents Anomalous behaviour of water.
when a liquid is heated up to a certain temperature, it expands, and when cooled it contracts. Water, however, shows a special and exceptional behaviour. If we heat water from 0 0C up to 4 0C, it contracts instead of expanding. At 4 0C its volume is minimum (due to contraction). If the water is heated further, it expands and its volume increases. The behaviour of water between its temperature from 0 0C to 4 0C is called anomalous behaviour of water.
3. What is meant by specific heat capacity? How will you prove experimentally that different substances have different specific heat capacities?
Answer:-
Definition:- The amount of heat energy required to raise the temperature of a unit mass of an object by 1 0C is called the specific heat of that object.
The specific heat capacity is denoted by letter ‘c’.
The SI unit of specific heat is J/ 0C kg, and the CGS unit is cal/g 0C.
If specific heat of an object is ‘c’, the mass of the object is ‘m’ and if the temperature
of the object is raised by ∆T 0C, the heat energy absorbed by the object is given by,
m X c X ∆T.
Procedure :
1. Take three spheres of iron, copper and lead of equal mass (Fig. 5.8)
2. Put all the three spheres in boiling water in the beaker for some time.
3. Take the three spheres out of the water. All the spheres will be at temperature 100 0C. Put them immediately on the thick slab
of wax.
4. Note, the depth that each of the sphere
goes into the wax.
The sphere which absorbs more heat from the water will give more heat to wax. More wax will thus melt and the sphere will go deeper in the wax. It can be observed that the iron sphere goes deepest into the wax. Lead sphere goes the least and copper sphere goes to intermediate depth. This shows that for equal rise in temperature, the three spheres have absorbed different amounts of heat. This means that the property which determines the amount of heat absorbed by a sphere is different for the three spheres. This property is called the specific heat capacity.
4. While deciding the unit for heat, which temperatures interval is chosen? Why?
Answer:- If we heat 1 kg of water by 10C in different temperature range than 14.5 0C to 15.5 0C, the amount of heat required will be slightly different. It is, therefore, essential to define a specific temperature range while defining the unit of heat. Calorie and Joule are related by following relation: 1 cal = 4.18 Joule5. Explain the following temperature versus time graph.
Answer:-
The given temperature versus time graph explains the behavior of water when heated continuously and uniformly. Line AB in the graph represents the conversion of ice into water at a constant temperature of 0°C. When ice is heated, it melts at 0°C and converts into water while maintaining a constant temperature of 0°C. This constant temperature is called the melting point of ice. During this transition, the ice absorbs heat energy, which is utilized for weakening the bonds between the atoms or molecules in the ice to transform itself into a liquid. This heat energy absorbed by the ice, at constant temperature, to convert it into a liquid is called the latent heat of fusion.
Once all the ice is transformed into water, the temperature of water starts rising. It increases up to 100°C. Line BC in the graph represents the rise in temperature of water from 0°C to 100°C. Thereafter, even though heat energy is supplied to water, its temperature does not rise. The heat energy is absorbed by water at this temperature and is used to break the bonds between molecules of the liquid and convert the liquid into the gaseous state. Thus, during the transformation from the liquid phase to the gas phase, heat energy is absorbed by the liquid, but its temperature does not change. The constant temperature at which the liquid transforms into the gaseous state is called the boiling point of the liquid. The heat energy absorbed at a constant temperature during the transformation of liquid into gas is called the latent heat of vaporization.
In summary, the graph depicts the temperature changes of water during the heating process, including the melting point of ice, the rise in temperature of water, the boiling point of water, and the conversion of water into steam.
6. Explain the following:
a. What is the role of anomalous behaviour of water in preserving aquatic life in regions of cold climate?
Answer:_
The anomalous behavior of water refers to its ability to expand upon freezing, unlike most other liquids that contract upon solidification. This property is essential for the preservation of aquatic life in regions of cold climate as the ice that forms on the surface of water acts as an insulating layer, preventing the water below from freezing completely. This allows aquatic life to survive the harsh winter months since the water below the ice remains in a liquid state, providing a habitat for fish, plants, and other organisms. Without this property of water, the entire water body would freeze solid, making it difficult or even impossible for aquatic life to survive. Thus, the anomalous behavior of water plays a crucial role in preserving aquatic life in regions of cold climate.
b. How can you relate the formation of water droplets on the outer surface of a bottle taken out of refrigerator with formation of dew?
Answer:-
The formation of water droplets on the outer surface of a bottle taken out of the refrigerator is due to the process of condensation. When the warm and moist air inside the bottle comes in contact with the cold surface of the bottle, the moisture in the air condenses and forms water droplets on the surface.
Similarly, the formation of dew occurs due to the process of condensation. During the night, the Earth’s surface radiates heat, causing the surface to cool. When the surface cools below the dew point temperature of the surrounding air, the moisture in the air condenses and forms tiny water droplets on the surface. This process is called dew formation.
Thus, the formation of water droplets on the outer surface of a bottle taken out of the refrigerator is similar to the formation of dew, as both are due to the process of condensation. The only difference is that in the case of dew, the condensation occurs on the surface of the Earth, whereas in the case of the bottle, it occurs on the outer surface of the bottle.
c. In cold regions in winter, the rocks crack due to anomalous expansion of water.
Answer:_
In cold regions during winter, rocks can crack due to the anomalous expansion of water. This happens because when water freezes, it expands by about 9% due to its anomalous expansion property, which exerts tremendous pressure on its surroundings. If there is water inside the cracks and crevices of the rocks, the expansion of the water upon freezing can generate sufficient force to break the rocks. This process is also known as frost weathering.
During the winter months, temperatures in cold regions drop significantly, causing water to freeze and expand. This expansion can cause the rocks to crack and break, leading to the formation of smaller rocks and pebbles. Over time, this process can also contribute to the formation of soil and the breakdown of larger rocks into smaller fragments.
The phenomenon of rocks cracking due to the anomalous expansion of water is not only limited to cold regions but can also occur in other areas with fluctuating temperatures or where water is present in cracks and crevices.
7. Answer the following:
a. What is meant by latent heat? How will the state of matter transform if latent heat is given off?
Answer:_
Latent heat is the amount of heat energy absorbed or released by a substance during a change in its state (solid, liquid, or gas) without a change in its temperature. It is the heat required to change the state of a substance without changing its temperature. When a substance absorbs latent heat, it can undergo a change of state, such as melting or vaporization.
For example, when ice is heated at its melting point, it absorbs latent heat from the surrounding environment to melt and transform into water. Similarly, when water is heated at its boiling point, it absorbs latent heat from the surrounding environment to vaporize and transform into steam. Conversely, when water vapor condenses to form liquid water or liquid water freezes to form ice, it releases latent heat to the surrounding environment.
If latent heat is given off, the state of matter will transform in the opposite direction of the change that absorbs the latent heat. For example, if ice releases latent heat, it will transform into liquid water. Similarly, if water vapor releases latent heat, it will transform into liquid water. The amount of latent heat released or absorbed during a change of state depends on the substance and the amount of substance involved.
b Which principle is used to measure the specific heat capacity of a substance?
Answer:- Principle of heat exchange is used to measure the specific heat capacity of a substance.
c. Explain the role of latent heat in the change of state of a substances?
Answer:_
The role of latent heat in the change of state of a substance is crucial. Latent heat is the amount of heat energy that is absorbed or released by a substance during a change in its state (solid, liquid, or gas) without a change in its temperature. When a substance absorbs latent heat, it can undergo a change of state, such as melting, evaporation or sublimation.
During these changes, the added heat energy is used to break the intermolecular bonds between the particles of the substance, rather than increasing their kinetic energy or temperature. When these bonds break, the particles are free to move from their fixed positions and the substance undergoes a change of state.
For example, when ice is heated, it absorbs latent heat energy from its surroundings, which breaks the intermolecular bonds between the water molecules and transforms the ice into liquid water. Similarly, when water is heated to its boiling point, it absorbs latent heat energy from its surroundings, which breaks the intermolecular bonds between the water molecules and transforms the water into water vapor.
Conversely, when a substance loses heat energy, it can undergo a reverse change of state, such as freezing, condensation or deposition. During these changes, the lost heat energy is used to form intermolecular bonds between the particles of the substance, rather than decreasing their kinetic energy or temperature.
For example, when water vapor loses latent heat energy, it condenses into liquid water, which forms intermolecular bonds between the water molecules. Similarly, when water loses latent heat energy, it freezes into ice, which forms intermolecular bonds between the water molecules.
Thus, latent heat plays a vital role in the changes of state of a substance by breaking or forming intermolecular bonds between the particles, without changing the temperature of the substance.