In the power plant of a nuclear submarine, the temperature

What are the four common phases of matter?

Problem 1E Alcohol evaporates more quickly than water at the same temperature. Which produces more cooling—alcohol or the same amount of water on your skin?

Problem 59E Why does a hot dog pant?

Problem 1P The quantity of heat ?Q? that changes the temperature ??T? of a mass ?m? of a substance is given by ?Q? = ?cm???T?, where ?c? is the specific heat capacity of the substance. For example, for H2O, ?c = 1 cal/g°C. And for a change of phase, the quantity of heat ?Q? that changes the phase of a mass?m? is ?Q? = ?mL?, where ?L? is the heat of fusion or heat of vaporization of the substance. For example, for H2O, the heat of fusion is 80 cal/g (or 80 kcal/kg) and the heat of vaporization is 540 cal/g (or 540 kcal/kg). Use these relationships to determine the number of calories to change (a) 1 kg of 0°C ice to 0°C ice water, (b) 1 kg of 0°C ice water to 1 kg of 100°C boiling water, (c) 1 kg of 100°C boiling water to 1 kg of 100°C steam, and (d) 1 kg of 0°C ice to 1 kg of 100°C steam.

Problem 2E You can determine wind direction by wetting your finger and holding it up in the air. Explain.

Problem 2P The specific heat capacity of ice is about 0.5 cal/g°C. Supposing that it remains at that value all the way to absolute zero, calculate the number of calories it would take to change a 1-g ice cube at absolute zero (?273°C) to 1 g of boiling water. How does this number of calories compare with the number of calories required to change the same gram of 100°C boiling water to 100°C steam?

Problem 2RQ Do the molecules in a liquid all have about the same speed, or do they have a wide variety of speeds?

Problem 3E When you step out of a swimming pool on a hot, dry day in the Southwest, you feel quite chilly. Why?

Problem 3P Find the mass of 0°C ice that 10 g of 100°C steam will completely melt.

Problem 3RQ What is evaporation, and why is it a cooling process? Exactly what is it that cools?

Problem 4E Why is sweating an efficient mechanism for cooling off on a hot day?

Problem 4P Consider 50 g of hot water at 80°C poured into a cavity in a very large block of ice at 0°C. What will be the final temperature of the water in the cavity? Show that 50 g of ice must melt in order to cool the hot water down to this temperature.

Problem 4RQ Why does warmer water evaporate more readily than cold water?

Problem 5E Why does blowing over hot soup cool the soup?

Problem 5P A 50-g chunk of 80°C iron is dropped into a cavity in a very large block of ice at 0°C. Show that 5.5 g of ice will melt. (The specific heat capacity of iron is 0.11 cal/g°C.)

Problem? ?5RQ What is sublimation?

Problem 6E Can you give two reasons why pouring a cup of hot coffee into a saucer results in faster cooling?

Problem 6P If you drop a piece of ice on a hard surface, the energy of impact will melt some of the ice. The higher it drops, the more ice will melt upon impact. Show that to completely melt a block of ice that falls without air drag, it should ideally be dropped from a height of 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, 335,000 J/kg). Do you see why the answer doesn’t depend on mass?]

Problem 7E What happens to the temperature of a pan of water when evaporation exceeds condensation?

Problem 7P A 10-kg iron ball is dropped onto a pavement from a height of 100 m. If half of the heat generated goes into 3 warming the ball, find the temperature increase of the ball. (In SI units, the specific heat capacity of iron is 450 J/kg°C.) Why is the answer the same for a ball of any mass?

Problem 7RQ Why is a steam burn more damaging than a burn from boiling water of the same temperature?

Problem 8E What is the source of energy that keeps the dunking bird in Figure 17.4 operating?

Problem 8P The heat of vaporization of ethyl alcohol is about 200 cal/g. If 2 kg of this fluid were allowed to vaporize in a refrigerator, show that 5 kg of ice would be formed from 0°C water.

Problem 8RQ Why do you feel uncomfortably warm on a hot and humid day?

Problem 9E An inventor claims to have developed a new perfume that lasts a long time because it doesn’t evaporate. Comment on this claim.

Problem 10RQ Why does water vapor in the air condense when the air is chilled?

Problem 11E Does a common electric fan cool the air in a room? If not, then why is it used in an overly warm room?

Problem 10E Pretend that all the molecules in a liquid have the same speed, not random speeds. Would evaporation of this liquid cause the remaining liquid to be cooled? Explain.

Problem 11RQ Why does warm, moist air form clouds when it rises?

Problem 12E 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 is cooled considerably. Explain.

Problem 12RQ What is the basic difference between a cloud and fog?

Problem 13RQ Distinguish between evaporation and boiling.

Problem 13E Why will wrapping a bottle in a wet cloth at a picnic often produce a cooler bottle than placing the bottle in a bucket of cold water?

Problem 14E The human body can maintain its customary temperature of 37°C on a day when the temperature is above 40°C. How is this done?

Does increased atmospheric pressure increase or decrease the boiling point of water? Why is this so?

Problem 15E Double-pane windows have nitrogen gas or very dry air between the panes. Why is ordinary air a poor idea?

Problem 15RQ Double-pane windows have nitrogen gas or very dry air between the panes. Why is ordinary air a poor idea?

Problem 16E Why are icebergs often surrounded by fog?

Problem 17E How does Figure 17.7 help explain the moisture that forms on the inside of car windows when you’re parking with your date on a cool night?

Problem 16RQ Why will water at the bottom of a geyser not boil when it is at 100°C?

Problem 17RQ What happens to the water pressure at the bottom of a geyser when some of the water above gushes out?

You know that the windows in your warm house get wet on a cold day. But can moisture form on the windows if the interior of your house is cold on a hot day? How is this different?

Problem? ?18RQ The temperature of boiling water doesn’t increase with continued energy input. Why is this evidence that boiling is a cooling process?

On freezing days, frost often forms on windows. Why is there usually more frost on the bottom portions of the windows?

Problem 19RQ When will water boil at a temperature of less than 100°C?

Problem 20RQ What evidence can you cite for the claim that water can boil at a temperature of 0°C?

Problem 20E Why do clouds often form above mountain peaks? (?Hint:? Consider the updrafts.)

Problem 21E Why will clouds tend to form above either a flat or a mountainous island in the middle of the ocean? (?Hint:? Compare the specific heat capacity of the land with that of the water and the subsequent convection currents in the air.)

Problem 21RQ Why does increasing the temperature of a solid make it melt?

Problem 22E A great amount of water vapor changes phase to become water in the clouds that form a thunderstorm. Does this release thermal energy or absorb it?

Problem 22RQ Why does decreasing the temperature of a liquid make it freeze?

Problem 23E When can you add heat to something without raising its temperature?

Problem 23RQ Why does freezing of water not occur at 0°C when foreign ions are present?

Problem 24E When can you withdraw heat from something without lowering its temperature?

Problem 24RQ What happens to the hexagonal open structure of ice when sufficient pressure is applied to it?

Problem 25E Why does the temperature of boiling water remain the same as long as the heating and boiling continue?

Problem 25RQ Why does a wire not simply cut a block of ice in two when it passes through the ice?

Problem 26E Why do vapor bubbles in a pot of boiling water increase in size as they rise in the water?

Problem 26RQ Does a liquid release energy or absorb energy when it changes into a gas?

Problem 27E Why does the boiling temperature of water decrease when the water is under reduced pressure, such as when it is at a higher altitude?

Problem 28E Place a jar of water on a small stand within a saucepan of water so that the bottom of the jar is held above the bottom of the pan. When the pan is placed on a stove, the water in the pan will boil, but not the water in the jar. Why?

Problem 27RQ Does a liquid release energy or absorb energy when it changes into a solid?

Problem 28RQ Is heat discharged at the back of a refrigerator and by a heat pump given off by vaporization of the refrigerating fluid or by condensation?

Problem 29E Hydrothermal vents are openings in the ocean floor that discharge very hot water. Water emerging at nearly 280°C from one such vent off the Oregon coast, some 2400 m beneath the surface, is not boiling. Provide an explanation.

Problem 29RQ How many calories are needed to change the temperature of 1 g of water by 1°C? To melt 1 g of ice at 0°C? To vaporize 1 g of boiling water at 100°C?

Problem 30E Water will boil spontaneously in a vacuum—on the surface of the Moon, for example. Could you cook an egg in this boiling water? Explain.

Problem 30RQ Cite two reasons why firewalkers don’t burn their wetted feet when walking barefoot on red-hot coals.

Problem 31E Our inventor friend proposes a design for cookware that will allow boiling to occur at a temperature less than 100°C so that food can be cooked with less energy consumption. Comment on this idea.

Problem 32E What can go wrong if you grasp the handle of a hot skillet with a wet thin dishcloth?

Problem 33E How can water be brought to a boil without heating it?

Problem 34E If water that boils due to reduced pressure is not hot, then is ice formed by the reduced pressure not cold? Explain.

Problem 35E Your instructor hands you a closed flask partly filled with room-temperature water. When you hold it, the heat transfer between your bare hands and the flask causes the water to boil. Quite impressive! How is this accomplished?

Problem 36E When you boil potatoes, will your cooking time be reduced with vigorously boiling water instead of gently boiling water? (Directions for cooking spaghetti call for vigorously boiling water—not to lessen cooking time but to prevent something else. If you don’t know what it is, ask a cook.)

Problem 38E In the power plant of a nuclear submarine, the temperature of the water in the reactor is above 100°C. How is this possible?

Problem 39E Explain why the eruptions of many geysers repeat with notable regularity.

Can ice be colder than \(0^\circ\)C? What is the temperature of an ice-water, mixture?

Problem 40E Why does the water in a car radiator sometimes boil explosively when the radiator cap is removed?

Problem 42E Why is very cold ice “sticky”?

Problem 43E How does the freezing point of a liquid compare with its melting point?

Problem 44E People who live where snowfall is common will tell you that air temperatures are higher when it’s snowing than when it's clear. Some misinterpret this by stating that snowfall can’t occur on very cold days. Explain this misinterpretation.

How might water be desalinized by freezing?

Problem 46E Would regelation occur if ice crystals did not have an open structure? Explain.

Problem 47E A piece of metal and an equal mass of wood are both removed from a hot oven at equal temperatures and are dropped onto blocks of ice. The metal has a lower specific heat capacity than the wood. Which will melt more ice before cooling to 0°C?

Problem 48E How does melting ice change the temperature of the surrounding air?

Problem 49E When you step inside a warm ski lodge on a cold day, you find your eyeglasses fog. Why does this occur?

What accounts for the bulged ends of a can of soda that has been frozen?

Problem 51E Why is half-frozen fruit punch always sweeter than completely melted fruit punch?

Problem 52E Air-conditioning units contain no water whatever, yet it is common to see water dripping from them when they’re operating on a hot day. Explain.

Problem 53E Is it condensation or vaporization that occurs on the warm outside coils of an operating air conditioner?

Problem 54E Some old-timers found that when they wrapped newspaper around the ice in their iceboxes, melting was inhibited. Discuss the advisability of this practice.

Problem 55E When ice in a pond melts, what effect does this have on the temperature of the nearby air?

Problem 56E Why is it that a tub of water placed in a farmer’s canning cellar helps prevent canned food from freezing in cold winters?

Problem 57E Why will spraying fruit trees with water before a frost help to protect the fruit from freezing?

Problem 58E How can devices that heat homes in winter also be used to cool homes in summer?

What are the four common phases of matter?

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

What is evaporation?

Why is evaporation a cooling process?

What is sublimation?

Distinguish between condensation and evaporation.

Why is a steam burn more damaging than a burn from boiling water at the same temperature?

Why do you feel uncomfortably warm on a hot and humid day?

Distinguish between humidity and relative humidity.

Why does water vapor in the air condense when the air is chilled?

Why does warm, moist air form clouds when it rises?

What is the basic difference between a cloud and fog?

Distinguish between evaporation and boiling.

Does increased atmospheric pressure increase or decrease the boiling point of water?

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

Why doesn’t the water at the bottom of a geyser boil when it is at \(100^{\circ} \mathrm{C}\)? Text Transcription: 100^circ C

What happens to the water pressure at the bottom of a geyser when some of the water above gushes out?

Why doesn’t energy added to boiling water increase the temperature of the water?

When will water boil at a temperature lower than \(100^{\circ} \mathrm{C}\)?

What evidence can you cite for the claim that water can boil at a temperature of \(0^{\circ} \mathrm{C}\)?

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

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

Why doesn’t water freeze at \(0^{\circ} \mathrm{C}\) when foreign ions are present? Text Transcription: 0^circ C

Why doesn’t a wire simply cut a block of ice in two when it passes through the ice?

What happens to the hexagonal open structure of ice when sufficient pressure is applied to it?

Does a liquid release energy or absorb energy when it changes into a gas?

Does a liquid release energy or absorb energy when it changes into a solid?

Does the heat that is discharged at the condensation coils following the compression pump of a refrigerator involve vaporization or condensation of the refrigerating liquid?

How many calories are needed to change the temperature of 1 g of water by \(1^{\circ} \mathrm{C}\)? To melt 1 g of ice at \(0^{\circ} \mathrm{C}\)? To vaporize 1 g of boiling water at \(100^{\circ} \mathrm{C}\)? Text Transcription: 1^circ C 0^circ C 100^circ C

Cite two reasons why firewalkers don’t burn their wetted feet when they walk barefoot on red-hot coals.

The quantity of heat with temperature change is \(Q=c m \Delta T\). For a change of phase of water it is Q = mL, where \(L_{f}\) is the heat of fusion, 80 cal/g, and \(L_{v}\) is the heat of vaporization, 540 cal/g. The quantity of heat Q that changes the temperature \(\Delta T\) of a mass m of a substance is given by \(Q=c m \Delta T\), where c is the specific heat capacity of the substance. For example, for \(\mathrm{H}_{2} \mathrm{O}, \quad c=1 \quad \mathrm{cal} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\). And for a change of phase, the quantity of heat Q that changes the phase of a mass m is Q = mL, where L is the heat of fusion or heat of vaporization of the substance. For example, for \(\mathrm{H}_{2} \mathrm{O}\), the heat of fusion is 80 cal/g (or 80 kcal/kg) and the heat of vaporization is 540 cal/g (or 540 kcal/kg). Use these relationships to determine the number of calories to change (a) 1 kg of \(0^{\circ} \mathrm{C}\) ice to \(0^{\circ} \mathrm{C}\) ice water, (b) 1 kg of \(0^{\circ} \mathrm{C}\) ice water to 1 kg of \(100^{\circ} \mathrm{C}\) boiling water, (c) 1 kg of \(100^{\circ} \mathrm{C}\) boiling water to 1 kg of \(100^{\circ} \mathrm{C}\) steam, and (d) 1 kg of \(0^{\circ} \mathrm{C}\) ice to 1 kg of \(100^{\circ} \mathrm{C}\) steam. Text Transcription: Q = cm Delta T L_f L_v H_2 O, c=1 cal / g cdot ^circ C H_2 O 0^circ C 100^circ C

The quantity of heat with temperature change is \(Q=c m \Delta T\). For a change of phase of water it is Q = mL, where \(L_{f}\) is the heat of fusion, 80 cal/g, and \(L_{v}\) is the heat of vaporization, 540 cal/g. The specific heat capacity of ice is about \(0.5 \quad \mathrm{cal} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\), and suppose that it remains at that value all the way to absolute zero. Calculate the number of calories it would take to change a 1-g ice cube at absolute zero (\(-273^{\circ} \mathrm{C}\)) to 1 g of boiling water. How does this number of calories compare with the number of calories required to change the same gram of \(100^{\circ} \mathrm{C}\) boiling water to \(100^{\circ} \mathrm{C}\) steam? Text Transcription: Q = cm Delta T L_f L_v 0.5 cal / g cdot ^circ C -273^circ C 100^circ C

The quantity of heat with temperature change is \(Q=c m \Delta T\). For a change of phase of water it is Q = mL, where \(L_{f}\) is the heat of fusion, 80 cal/g, and \(L_{v}\) is the heat of vaporization, 540 cal/g. Find the mass of \(0^{\circ} \mathrm{C}\) ice that 10 g of \(100^{\circ} \mathrm{C}\) steam will completely melt. Text Transcription: Q = cm Delta T L_f L_v 0^circ C 100^circ C

The quantity of heat with temperature change is \(Q=c m \Delta T\). For a change of phase of water it is Q = mL, where \(L_{f}\) is the heat of fusion, 80 cal/g, and \(L_{v}\) is the heat of vaporization, 540 cal/g. Consider 50 g of hot water at \(80^{\circ} \mathrm{C}\) poured into a cavity in a very large block of ice at \(0^{\circ} \mathrm{C}\). What will be the final temperature of the water in the cavity? Show that 50 g of ice must melt in order to cool the hot water down to this temperature. Text Transcription: Q = cm Delta T L_f L_v 80^circ C 0^circ C

The quantity of heat with temperature change is \(Q=c m \Delta T\). For a change of phase of water it is Q = mL, where \(L_{f}\) is the heat of fusion, 80 cal/g, and \(L_{v}\) is the heat of vaporization, 540 cal/g. A 50-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 5.5 g of ice will melt. (The specific heat capacity of iron is \(0.11 \quad \mathrm{cal} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\).) Text Transcription: Q = cm Delta T L_f L_v 80^circ C 0^circ C 0.11 cal / g cdot ^circ C

The quantity of heat with temperature change is \(Q=c m \Delta T\). For a change of phase of water it is Q = mL, where \(L_{f}\) is the heat of fusion, 80 cal/g, and \(L_{v}\) is the heat of vaporization, 540 cal/g. If you drop a piece of ice on a hard surface, the energy of impact will melt some of the ice. The farther the ice drops, the more ice will melt upon impact. Show that to completely melt a block of ice that falls without air drag, it should ideally be dropped from a height of 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, 335,000 J/kg). Do you see why the answer doesn’t depend on mass?]

The quantity of heat with temperature change is \(Q=c m \Delta T\). For a change of phase of water it is Q = mL, where \(L_{f}\) is the heat of fusion, 80 cal/g, and \(L_{v}\) is the heat of vaporization, 540 cal/g. The heat of vaporization of ethyl alcohol is about 200 cal/g. If 2 kg of this fluid were allowed to vaporize in a refrigerator, show that 5 kg of ice would be formed from \(0^{\circ} \mathrm{C}\) water.

The quantity of heat with temperature change is \(Q=c m \Delta T\). For a change of phase of water it is Q = mL, where \(L_{f}\) is the heat of fusion, 80 cal/g, and \(L_{v}\) is the heat of vaporization, 540 cal/g. A 10-kg iron ball is dropped onto a pavement from a height of 100 m. If half of the heat generated goes into warming the ball, find the temperature increase of the ball. (In SI units, the specific heat capacity of iron is \(450 \quad \mathrm{J} / \mathrm{kg} \cdot{ }^{\circ} \mathrm{C}\).) Why is the answer the same for a ball of any mass? Text Transcription: Q = cm Delta T L_f L_v 450 J / kg cdot ^circ C

Rank the boiling-water temperatures from highest to lowest in these locations: a. Death Valley, b. sea level, c. Denver, CO (the “mile-high city”).

From greatest to least, rank the energies 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

When you step out of a swimming pool on a hot, dry day in the Southwest, you feel quite chilly. Why?

Why is sweating an efficient mechanism for cooling off on a hot day?

Why does blowing over hot soup cool the soup?

What happens to the temperature of a pan of water when evaporation exceeds condensation?

What is the source of energy that keeps the dunking bird in Figure 17.4 operating?

An inventor claims to have developed a new perfume that lasts a long time because it doesn’t evaporate. Comment on this claim.

Does a common electric fan cool the air in a room? If not, then why is it used in an overly warm room?

Why will wrapping a bottle in a wet cloth at a picnic often produce a cooler bottle than placing the bottle in a bucket of cold water?

The human body can maintain its customary temperature of \(37^{\circ} \mathrm{C}\) on a day when the temperature is above \(40^{\circ} \mathrm{C}\). How is this done?

Double-pane windows have nitrogen gas or very dry air between the panes. Why is ordinary air a poor idea?

Why are icebergs often surrounded by fog?

How does Figure 17.8 help explain the moisture that forms on the inside of car windows when you’re parking with your date on a cool night?

You know that the windows in your warm house get wet on a cold day. But can moisture form on the windows if the interior of your house is cold on a hot day? How is this different?

On freezing days, frost often forms on windows. Why is there usually more frost on the bottom portions of the windows?

Why do clouds often form above mountain peaks? (Hint: Consider the updrafts.)

Why do clouds tend to form above either a flat or a mountainous island in the middle of the ocean? (Hint: Compare the specific heat capacity of the land with that of the water and the subsequent convection currents in the air.)

A great amount of water vapor changes phase to become water in the clouds that form a thunderstorm. Does this process release thermal energy or absorb it?

Why does the temperature of boiling water remain the same as long as the heating and boiling continue?

Why do vapor bubbles in a pot of boiling water increase in size as they rise in the water?

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

Place a jar of water on a small stand in a saucepan of water so that the bottom of the jar is held above the bottom of the pan. When the pan is placed on a stove, the water in the pan will boil but the water in the jar will not. Why?

Water will boil spontaneously in a vacuum—on the surface of the Moon, for example. Could you cook an egg in this boiling water? Explain.

Hydrothermal vents are openings in the ocean floor that discharge very hot water. Water emerging at nearly \(280^{\circ} \mathrm{C}\) from one such vent off the Oregon coast, some 2400 m beneath the surface, is not boiling. Provide an explanation. Text Transcription: 280^circ C

Our inventor friend proposes a design for cookware that will allow boiling to occur at a temperature lower than \(100^{\circ} \mathrm{C}\) so that food can be cooked with less energy consumption. Comment on this idea. Text Transcription: 100^circ C

What can go wrong if you grasp the handle of a hot skillet with a wet thin dishcloth?

How can water be brought to a boil without heating it?

If water that boils due to reduced pressure is not hot, then is ice formed by reduced pressure not cold? Explain.

Your instructor hands you a closed flask partly filled with room-temperature water. When you hold it, the heat transfer between your bare hands and the flask causes the water to boil. Quite impressive! How is this accomplished?

When you boil potatoes, will the cooking time be reduced with vigorously boiling water instead of gently boiling water? (Directions for cooking spaghetti call for vigorously boiling water—not to lessen cooking time but to prevent something else. If you don’t know what it is, ask a cook.)

Why does placing a lid over a pot of water on a stove shorten the time it takes for the water to come to a boil, whereas, after the water is boiling, the use of a lid only slightly shortens the cooking time?

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

Explain why the eruptions of many geysers repeat with notable regularity.

Why does the water in a car radiator sometimes boil explosively when the radiator cap is removed?

Can ice be colder than \(0^{\circ} \mathrm{C}\)? What is the temperature of an ice–water mixture?

Why is very cold ice “sticky”?

How does the freezing point of a liquid compare with its melting point?

People who live where snowfall is common will tell you that air temperatures are higher when it’s snowing than when it’s clear. Some misinterpret this by stating that snowfall can’t occur on very cold days. Explain this misinterpretation.

How might water be desalinized by freezing?

What produces the wet underside of a glacier, which enables it to slip down elevated regions?

Would regelation occur if ice crystals did not have an open structure? Explain.

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

When you step inside a warm ski lodge on a cold day, your eyeglasses fog up. Why does this occur?

How does melting ice change the temperature of the surrounding air?

What accounts for the bulged ends of a can of soda that has been frozen?

Why is half-frozen fruit punch always sweeter than completely melted fruit punch?

Is it condensation or vaporization that occurs on the warm outside coils of an operating air conditioner?

When ice in a pond melts, what effect does this have on the temperature of the nearby air?

Some old-timers found that when they wrapped newspaper around the ice in their iceboxes, melting was inhibited. Discuss the advisability of this practice.

Why is it that a tub of water placed in a farmer’s canning cellar helps prevent canned food from freezing in cold winters?

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

How can devices that heat homes in winter also be used to cool homes in summer?

Why does a hot dog pant?

Alcohol evaporates more quickly than water at the same temperature. Discuss which produces more cooling: alcohol or the same amount of water on your skin.

You can determine the wind direction by wetting your finger and holding it up in the air. Discuss why.

There is more than a single reason why pouring a cup of hot coffee into a saucer results in faster cooling. Discuss two reasons.

Pretend that all the molecules in a liquid have the same speed, not random speeds. Would evaporation of this liquid cause the remaining liquid to be cooled? Discuss.

Porous canvas bags filled with water are used by travelers in hot weather. Discuss why, when the bags are slung on the outside of a fast-moving car, the water inside is cooled considerably.

When can you add heat to ice without melting it?

When can you add heat to something without raising its temperature?

When can you withdraw heat from something without lowering its temperature?

Discuss why water can issue from deep underwater vents at temperatures of some \(300^{\circ} \mathrm{C}\) without boiling.

Discuss what the predominant gas is in a bubble of boiling water.

Air-conditioning units contain no water whatever, yet it is common to see water dripping from them when they’re operating on a hot day. Discuss.