?BoilingWhy does putting a lid over a pot of water on a stove shorten the time needed

Show that 9300 cal of heat is needed to change 15 g of \(20^{\circ} \mathrm{C}\) water to \(100^{\circ} \mathrm{C}\) steam. Text Transcription: 20^circ C 100^circ C

Show that 100 g of \(100^{\circ} \mathrm{C}\) steam will completely melt 800 g of \(0^{\circ} \mathrm{C}\) ice. Text Transcription: 100^circ C 0^circ C

A small block of ice at \(0^{\circ} \mathrm{C}\) is subjected to 10 g of \(100^{\circ} \mathrm{C}\) steam and melts completely. Show that the mass of the block of ice can be no more than 80 g. Text Transcription: 0^circ C 100^circ C

The specific heat capacity of ice is about \(0.5\mathrm{\ cal}/\mathrm{g}^{\circ}\mathrm{C}\). Suppose it remains at that value all the way to absolute zero. (a) Show that the quantity of heat needed to change a 1-g ice cube at absolute zero \(\left(-273^{\circ} \mathrm{C}\right)\) to 1-g of boiling water is 320 cal. (b) How does 320 calories compare to the energy needed to simply bring 1-g of \(100^{\circ} \mathrm{C}\) water to a boil? Text Transcription: 0.5 cal/g^circ C (-273^circ C) 100^circ C

A 10-kg iron ball is dropped onto a pavement from a height of 100 m. Suppose that half of the heat generated goes into warming the ball. (a) Show that the temperature increase of the ball is \(1.1^{\circ} \mathrm{C}\). (In SI units, the specific heat capacity of iron is \(450 \mathrm{~J} / \mathrm{kg}^{\circ} \mathrm{C}\). Use 9.8 N/kg for g.) (b) Why is the answer the same for an iron ball of any mass? Text Transcription: 1.1^circ C 450 J/kg^circ C

A block of ice at \(0^{\circ} \mathrm{C}\) is dropped and completely melts upon impact. Assume that there is no air resistance and that all the energy goes into melting the ice. (a) Show that the height necessary for this to occur is at least 34 km. [Hint: Equate the joules of gravitational potential energy to the product of the mass of ice and its heat of fusion (in SI units, \(L_{\mathrm{f}}=335,000\mathrm{\ J}/\mathrm{kg}\)).] (b) Explain why the answer doesn’t depend on mass. Text Transcription: 0^circ C L_f=335,000 J/kg

Fifty grams of hot water at \(80^{\circ} \mathrm{C}\) is poured into a cavity in a very large block of ice at \(0^{\circ} \mathrm{C}\). The final temperature of the water in the cavity becomes \(0^{\circ} \mathrm{C}\). Show that the mass of ice that melts is 50 g. Text Transcription: 80^circ C 0^circ C

A 100-g chunk of \(80^{\circ} \mathrm{C}\) iron is dropped into a cavity in a very large block of ice at \(0^{\circ} \mathrm{C}\). Show that the mass of ice that melts is 11 g. (The specific heat capacity c of iron is \(0.11\mathrm{\ cal}/\mathrm{g}^{\circ}\mathrm{C}\).) Text Transcription: 80^circ C 0^circ C 0.11 cal/g^circ C

The heat of vaporization of ethyl alcohol \(L_{\mathrm{v}}\) is about 200 cal/g. Show that if 4 kg of this refrigerant were allowed to vaporize in a refrigerator, it could freeze 10 kg of \(0^{\circ} \mathrm{C}\) water to ice. Text Transcription: L_v 0^circ C

From greatest to lowest, rank these materials for conducting heat: (a) Copper wire. (b) Snow. (c) Glass rod.

From greatest to least, rank the frequency of radiation of these emitters of radiant energy: (a) Red-hot star. (b) Blue-hot star. (c) Sun.

Rank the boiling-water temperatures at the following locations from highest to lowest: (a) Death Valley (below sea level). (b) Sea level. (c) Denver, Colorado (the “mile-high city”).

From greatest to least, rank the energy needed for these phase changes for equal amounts of \(\mathrm{H}_{2} \mathrm{O}\). (a) From ice to ice-water. (b) From ice-water to boiling water. (c)From boiling water to steam. Text Transcription: H_2 O

Conduction Between the act of standing barefoot on top of an igloo and being inside, when does snow act as a conductor and when does it act as an insulator?

Conduction Which will cool your finger faster, touching a nail stuck in ice or touching the surface of the ice? Explain.

Conduction Wood is a better insulator than glass. Yet fiberglass is commonly used as an insulator in wooden buildings. Explain.

Conduction Visit a snow-covered cemetery and note that the snow does not slope upward against the gravestones but, instead, forms depressions around them, as shown. What is your explanation for this?

Conduction Wood has a very low conductivity. Does it still have a low conductivity if it is very hot—that is, in the stage of smoldering red-hot coals? Could you safely walk across a bed of red-hot wooden coals with bare feet? Although the coals are hot, does much heat conduct from them to your feet if you step quickly? Could you do the same on pieces of red-hot iron? Explain. (CAUTION: Coals can stick to your feet, so OUCH—don’t try this!)

Conduction What is the purpose of the copper or aluminum layer on the bottom of a stainless-steel pot?

Conduction Many tongues have been injured by licking a piece of metal on a very cold day. Why would little harm result if one licked a piece of wood on the same day?

Conduction What is the role of “loose” electrons in heat conductors?

Conduction What is the explanation for a barefoot firewalker being able to walk safely on red-hot wooden coals?

Conduction Does a good insulator prevent heat from getting through it, or does it simply delay its passage?

Convection By what means is heat transferred by convection?

Convection What happens to the temperature of air when it expands?

Convection Why is Millie’s hand not burned when she holds it above the escape valve of the pressure cooker (Figure 7.8)?

Convection Why does the direction of coastal winds change from day to night?

Radiation How is the peak frequency of radiant energy related to the absolute temperature of the radiating source?

Radiation What is terrestrial radiation? How does it differ from solar radiation?

Radiation All objects emit energy to their surroundings, so why don’t the temperatures of all objects continuously decrease?

Radiation Why does the pupil of the eye appear black?

Newton’s Law of Cooling Does a red-hot poker radiate more when it is placed in a warm oven, or when it is placed in a cold room? (Or does it radiate the same in both)?

Newton’s Law of Cooling Is the rate of cooling of a red-hot poker greater in a warm oven than in a cold room? (Or is the rate the same for each?)

Newton’s Law of Cooling Does Newton’s law of cooling apply to warming as well as to cooling?

Climate Change and the Greenhouse Effect What would be the consequence to Earth’s climate if the greenhouse effect were completely eliminated?

Climate Change and the Greenhouse Effect What is meant by the expression “You can never change only one thing?”

Heat Transfer and Change of Phase What are the four common phases of matter?

Heat Transfer and Change of Phase Do all the molecules in a liquid have about the same speed, or do they have a wide variety of speeds?

Heat Transfer and Change of Phase What is evaporation, and why is it a cooling process?

Heat Transfer and Change of Phase What is sublimation?

Heat Transfer and Change of Phase What is condensation, how does it differ from evaporation, and why is it a warming process?

Heat Transfer and Change of Phase Why is a steam burn more damaging than a burn from boiling water of the same temperature?

Boiling Distinguish between evaporation and boiling.

Boiling Why does water not boil at \(100^{\circ} \mathrm{C}\) when it is under greater-than-normal atmospheric pressure? Text Transcription: 100^circ C

Boiling Is it the boiling of the water or the higher temperature of the water that cooks food faster in a pressure cooker?

Melting and Freezing Why does increasing the temperature of a solid make it melt?

Melting and Freezing Why does decreasing the temperature of a liquid make it freeze?

Melting and Freezing Why doesn’t water freeze at \(0^{\circ} \mathrm{C}\) when it contains dissolved materia? Text Transcription: 0^circ C

Energy and Change of Phase Does a liquid give off energy or absorb energy when it changes into a gas? When it changes into a solid?

Energy and Change of Phase Does a gas give off energy or absorb energy when it changes into a liquid? How about a solid changing into a liquid?

Write a letter to your grandparents telling them that you’re learning about the connections of nature and distinguishing between closely related ideas. Use the concepts of heat and temperature as your example. Then explain how boiling water to make tea is actually a process that cools the water. Explain how your grandparents could convince their teatime friends of this intriguing concept.

Do as Megan shows in Figure 7.7 and blow on your hand, first with your mouth wide open, then with your lips puckered so that air expands more when exiting your mouth. Account for the temperature differences.

If you live where there is snow, do as Benjamin Franklin did more than 200 years ago, lay samples of light and dark cloth on the snow and note the differences among the rates of melting beneath the samples of cloth.

Hold the bottom end of a test tube full of cold water in your hand. Heat the top part in a flame until the water boils. That you can still hold the bottom shows that water (as well as glass) is a poor conductor of heat. This is even more dramatic when you wedge chunks of ice with steel wool at the bottom; then the water above can be brought to a boil without melting the ice! Try it and see.

Wrap a piece of paper around a thick metal bar, and place it in a flame. Note that the paper does not catch fire. Can you figure out why? (Paper generally does not ignite until its temperature reaches \(233^{\circ} \mathrm{C}\).) Text Transcription: 233^circ C

Place a Pyrex funnel mouth down in a saucepan full of water in such a way that the straight tube of the funnel protrudes above the water. Rest a part of the funnel on a nail or coin so that water can get under it. Place the pan on a stove, and observe the water as it begins to boil. Where do the bubbles form first? Why? As the bubbles rise, they expand rapidly and push water ahead of them. The funnel confines the water, which is forced up the tube and driven out at the top. Now do you know how a geyser and a coffee percolator operate?

Observe the spout of a teakettle of boiling water. Notice that you cannot see the steam that issues from the spout. The cloud that you see farther away from the spout is not steam, but condensed water droplets. Now hold the flame of a candle in the cloud of condensed steam. Can you explain your observations?

You can make rain in your kitchen. Put a cup of water in a Pyrex saucepan, and heat it slowly over a low flame. When the water is warm, place a saucer filled with ice cubes on top of the container. As the water below is heated, droplets form at the bottom of the cold saucer and combine until they are large enough to fall, producing a steady “rainfall” as the water below is gently heated. How does this resemble—and how does it differ from—the way that natural rain forms?

Suspend an open-topped container of water in a pan of boiling water, with its top above the surface of the boiling water. You’ll note that although water in the inner container can reach \(100^{\circ} \mathrm{C}\), it can’t boil. Can you explain why this is so? Text Transcription: 100^circ C

Show that 5000 cal of heat is needed to increase the temperature of 50 g water from \(0^{\circ} \mathrm{C}\) to \(100^{\circ} \mathrm{C}\). The specific heat capacity for water is \(1\mathrm{\ cal}/\mathrm{g}^{\circ}\mathrm{C}\). Text Transcription: 0^circ C 100^circ C 1 cal/g^circ C

Calculate the quantity of heat absorbed by 20 g of water that warms from \(30^{\circ} \mathrm{C}\) to \(90^{\circ} \mathrm{C}\). Text Transcription: 30^circ C 90^circ C

Show that 4000 cal of heat is needed to melt 50 g of \(0^{\circ} \mathrm{C}\) ice. The heat of fusion \(L_{f}\) for water is 80 cal/g. Text Transcription: 0^circ C L_f

Calculate the quantity of heat needed to melt a 200-g block of ice at \(0^{\circ} \mathrm{C}\). Text Transcription: 0^circ C

Show that 27,000 cal is needed to turn 50 g of \(100^{\circ} \mathrm{C}\) boiling water into steam. The heat of vaporization for water \(L_{\mathrm{v}}\) is 540 cal/g. Text Transcription: 100^circ C L_v

Calculate the quantity of heat needed to turn 200 g of \(100^{\circ} \mathrm{C}\) water to steam at the same temperature. Text Transcription: 100^circ C

Show that a total of 36,000 calories is needed to change 50 g of \(0^{\circ} \mathrm{C}\) ice to steam at \(100^{\circ} \mathrm{C}\). Text Transcription: 0^circ C 100^circ C

Convection How does buoyancy play a role in the rising of a parcel of warm air?

Convection When air is rapidly compressed, why does its temperature increase?

Convection When you blow air onto your hand from your wide-open mouth, your hand is warmed. Why is your hand cooled if you pucker your lips when blowing?

Convection Snowmaking machines used at ski areas blow a mixture of compressed air and water through a nozzle. The temperature of the mixture may initially be well above the freezing temperature of water, yet crystals of snow are formed as the mixture is ejected from the nozzle. Explain how this happens.

Radiation From a position near an incandescent lamp, turn it on and off quickly. While it is briefly on you feel its heat, but when you touch the bulb, you find that it is not hot. Explain why you felt heat from the lamp.

Radiation The source of the heat of volcanoes and natural hot springs is trace amounts of radioactive minerals in common rock in Earth’s interior. Why isn’t the same kind of rock at Earth’s surface warm to the touch?

Radiation What does the formula f ~ T tell us about what radiates and what doesn’t?

Radiation If everything radiates, why doesn’t everything zoom downward in temperature?

Radiation What is the name given to radiant energy emitted by Earth? How does it differ from radiation emitted by the Sun?

Radiation Using as a guide the rule that a good absorber of radiation is a good radiator and the rule that a good reflector is a poor absorber, state a rule relating the reflection and radiation properties of a surface.

Radiation You enter a crowded and chilly classroom early in the morning on a cold winter day. Before the end of the hour, the room temperature increases to a comfortable level, even if heat is not provided by the school heating system. Why the difference?

Radiation In terms of physics, why do restaurants serve baked potatoes wrapped in aluminum foil?

Newton’s Law of Cooling Why isn’t it important to convert temperatures to the Kelvin scale when we use Newton’s law of cooling?

Newton’s Law of Cooling Which decreases in temperature more rapidly, a whitehot poker or a red-hot poker? Or do they cool at the same rate?

Newton’s Law of Cooling Which will warm by \(15^{\circ} \mathrm{C}\) quicker in a \(100^{\circ} \mathrm{C}\) oven: a \(10^{\circ} \mathrm{C}\) piece of pie or a \(20^{\circ} \mathrm{C}\) piece of pie? Text Transcription: 15^circ C 100^circ C 10^circ C 20^circ C

Climate Change and the Greenhouse Effect Why is a water-based white solution (whitewash) sometimes applied to the glass of florists’ greenhouses? Would you expect this practice to be more prevalent in the winter or in the summer?

Climate Change and the Greenhouse Effect If the composition of the atmosphere were changed so that it permitted a greater amount of terrestrial radiation to escape, what effect would this have on Earth’s climate?

Climate Change and the Greenhouse Effect Consider the solar energy that enters a florist’s greenhouse and is absorbed by plants. Why is the energy that is reradiated by the plants of much lower frequency than the solar energy?

Climate Change and the Greenhouse Effect What does the planet Venus have to do with Earth’s greenhouse effect?

Heat Transfer and Change of Phase Alcohol evaporates more rapidly than water at the same temperature. Which produces more cooling: alcohol or the same amount of water on your skin?

Heat Transfer and Change of Phase You can determine wind direction by wetting your finger and holding it up in the air. Explain.

Heat Transfer and Change of Phase Why does a dog pant when it is hot?.

Heat Transfer and Change of Phase Give two reasons why pouring a cup of hot coffee into a saucer results in faster cooling?

Heat Transfer and Change of Phase Porous canvas bags filled with water are used by travelers in hot weather. When the bags are slung on the outside of a fast-moving car, the water inside the bags is cooled considerably. Explain.

Heat Transfer and Change of Phase Why does wrapping a bottled beverage in a wet cloth at a picnic often produce a cooler bottle than placing the bottle in a bucket of cold water?

Heat Transfer and Change of Phase A friend says that the reason why you feel uncomfortable in muggy weather is that water molecules in the air are giving up energy while bombarding you. Do you agree or disagree with your friend?

Heat Transfer and Change of Phase Erik Wong crunches an aluminum soft-drink can on page 180. Is the can sucked in by the partial vacuum created, or pushed inward by atmospheric pressure? Or both?

Heat Transfer and Change of Phase Double-pane windows have nitrogen gas or very dry air between the panes. Why is using ordinary air between the panes a poor idea?

Boiling Boiling can be brought about by increasing the temperature of water. How can boiling be brought about without increasing water temperature?

Boiling Why does the boiling temperature of water decrease when the water is under reduced pressure, such as at a higher altitude?

Boiling Room-temperature water boils spontaneously in a vacuum—on the Moon, for example. Could you cook an egg in this boiling water? Explain.

Boiling Your inventor friend proposes a design for cookware that allows boiling to take place below \(100^{\circ} \mathrm{C}\) so that food can be cooked with less energy. Comment on this idea. Text Transcription: 100^circ C

Boiling When boiling spaghetti, is your cooking time reduced if the water is vigorously boiling instead of gently boiling?

Boiling Why does putting a lid over a pot of water on a stove shorten the time needed for the water to come to a boil, whereas after the water boils, the use of the lid only slightly shortens the cooking time?

Boiling In the power plant of a nuclear submarine, the temperature of the water in the reactor is above \(100^{\circ} \mathrm{C}\). How is this possible? Text Transcription: 100^circ C

Melting and Freezing Distinguish between melting and freezing in terms of molecular speeds.

Melting and Freezing How do the temperature at which a particular metal melts and the temperature at which it freezes compare?

Melting and Freezing Discuss why half-frozen fruit punch is always sweeter than completely melted fruit punch.

Melting and Freezing What role does antifreeze play in preventing the freezing of water?

Energy and Change of Phase When can you add heat to a substance without raising its temperature? Give an example.

Energy and Change of Phase When can you withdraw heat from a substance without lowering its temperature? Give an example.

Energy and Change of Phase What does an air conditioner have in common with a refrigerator?

Energy and Change of Phase Air-conditioning units contain no water whatsoever, yet it is common to see water dripping from operating outdoor air conditioners on homes on a hot day. Explain.

Energy and Change of Phase For water, which has the higher value: heat of fusion or heat of vaporization?

Energy and Change of Phase Your friend says that more thermal energy is needed to increase a gram of water from absolute zero to its boiling point than is needed to boil the water once it reaches \(100^{\circ} \mathrm{C}\). Do you agree or disagree? Text Transcription: 100^circ C

Wrap part of a fur coat around a thermometer. Discuss whether or not the temperature rises.

What is the principal reason why a feather quilt is so warm on a cold winter night?

Friends in your discussion group say that when you touch a piece of ice, cold “flows” from the ice to your hand, which is why your hand is cooled. What is your more enlightened response?

If all the molecules in a liquid had the same speed, and some were able to evaporate, would the remaining liquid be cooled? Explain.

What is the source of energy that keeps the dunking bird in Figure 7.28 operating?

How do the average kinetic energies of hydrogen and oxygen gases compare when these two gases are mixed at the same temperature? How do the average speeds of their molecules compare? Discuss how mass is the crux of these questions.

In a mixture of U-238 and U-235 isotopes, which atoms have the greater average speed? How would this affect diffusion through a porous membrane of otherwise identical gases made from these isotopes? Link this to the previous question.

A number of objects at different temperatures placed in a closed room share radiant energy and ultimately come to the same temperature. Would this thermal equilibrium be possible if good absorbers were poor emitters and poor absorbers were good emitters? Defend your answer.

Why can you drink a cup of boiling-hot tea atop a high mountain without any danger of burning your lips? What if you did this in a mine shaft below sea level?

Hydrothermal vents are openings in the ocean floor that discharge water at temperatures far exceeding \(100^{\circ} \mathrm{C}\) . Discuss why this water is not boiling. Text Transcription: 100^circ C

Suppose that at a restaurant, you are served coffee before you are ready to drink it. In order that it be as hot as possible when you are ready for it, would you be wiser to add cream to it right away or to add cream just before you are ready to drink it? This question should elicit much discussion!

If you wish to save fuel and you’re going to leave your warm house for half an hour or so on a very cold day, should you turn your thermostat down a few degrees, turn it off altogether, or let it remain at your preferred room temperature? This question should elicit much discussion!

If you wish to save fuel and you’re going to leave your cool house for half an hour or so on a very hot day, should you turn your air-conditioning thermostat up a bit, turn it off altogether, or let it remain at your preferred room temperature? This question should elicit much discussion!

Place a jar of water on a small stand on the bottom of a saucepan of water. Then the bottom of the jar is positioned above the bottom of the pan. When the pan is put on a stove, the water in the pan boils, but the water in the jar does not. Why?

A piece of metal and an equal mass of wood are both removed from a hot oven at equal temperatures and dropped onto blocks of ice. The wood has a higher specific heat capacity than the metal. Which melts more ice before cooling to \(0^{\circ} \mathrm{C}\) ? Text Transcription: 0^circ C

Earth scientists are considering a means of inducing clouds to be a brighter white. What effect would this have on Earth’s climate?

Why does placing a tub of water in a farmer’s canning cellar help prevent canned food from freezing in cold winters?

Why does spraying fruit trees with water before a frost help protect the fruit from freezing?

The snow-covered mailboxes raise a question: What explains why the light-colored ones are snow covered, while the black ones are free of snow?