Module # 4: Chapters 15-17
Does a good insulator prevent heat from escaping or slow its passage?
Insulation delays heat transfer
What is meant by "translational" kinetic energy?
Kinetic energy that goes to and fro in molecular motion.
Why does the direction of coastal winds change from day to night?
The direction of wind changes with changes in land and water temperatures. Airflow reverses as relative temperatures reverse.
Does Newton's law of cooling apply to warming as well as to cooling?
Yes
To say that water has a high specific heat capacity is to say that water a.requires a lot of energy in order to increase in temperature. b.gives off a lot of energy in cooling. c.absorbs a lot of energy for a small increase in temperature. d.All of these.
d.All of these.
The high specific heat capacity of water has great importance in a.climates. b.cooling systems. c.ocean currents. d.All of these.
d.All of these.
What is the role of "loose" electrons in heat conductors?
"Loose" Electrons move quickly and transfer energy to other electrons that migrate through the mineral.
Distinguish between a calorie and a joule.
1 calorie is equal to 4.19 Joules.
Rank the boiling-water temperatures from highest to lowest in these locations: Death Valley, sea level, Denver, CO (the "mile-high city")
1,2,3
What was the precise temperature at the bottom of Lake Michigan, where the water is deep and the winters long, on New Year's Eve in 1901?
4°C because the temperature at the bottom of any body of water containing any 4°C water has a bottom temperature of 4°C, for the same reason that rocks are at the bottom. Rocks are more dense than water, and 4°C water is more dense than water at any other temperature. So both rocks and 4°C water sink to the bottom. Water is also a poor heat conductor, so if the body of water is deep and in a region of long winters and short summers, the water at the bottom likely remains a constant 4°C year-round.
Which will normally warm faster: a black pot of cold water or a silvered pot of cold water? Which will cool faster?
A black pot will warm faster (and cools faster) than a silver pot.
If a fast marble hits a random scatter of slow marbles, does the fast marble usually speed up or slow down? Of the initially fast-moving marble and the initially slow ones, which lose(s) kinetic energy and which gain(s) kinetic energy? How do these questions relate to the direction of heat flow?
A fast-moving marble slows when it hits slower-moving marbles. It transfers some of its kinetic energy to the slower ones. Likewise with the flow of heat. Molecules with more kinetic energy that are in contact with molecules that have less kinetic energy transfer some of their excess energy to the less energetic ones. The direction of energy transfer is from hot to cold. For both the marbles and the molecules, however, the total energy before and after contact is the same.
Temperature
A measure of the average translational kinetic energy per molecule in a substance, measured in degrees Celsius or Fahrenheit or in kelvins (K).
Does a substance that cools off quickly have a high or a low specific heat capacity?
A substance that cools quickly has a low specific heat capacity.
In desert regions that are hot in the daytime and cold at nighttime, the walls of houses are often made of mud. Why is it important that the mud walls be thick?
A wall of appropriate thickness keeps the house warm at night by slowing the flow of heat from inside to outside, and it keeps the house cool in the daytime by slowing the flow of heat from outside to inside. Such a wall has "thermal inertia."
Ethyl alcohol has about one-half the specific heat capacity of water. If equal masses of each at the same temperature are supplied with equal quantities of heat, which will undergo the greater change in temperature?
Alcohol, because less specific heat means less thermal inertia and a greater change in temperature.
Why does warm, moist air form clouds when it rises?
As the air rises, it cools and condenses to form clouds.
Three blocks of metal at the same temperature are placed on a hot stove. Their specific heat capacities are listed below. Rank them from greatest to least in how quickly each warms up. A.)Steel, 450 J/kg⋅°C B.)Aluminum, 910 J/kg⋅°C C.) Copper, 390 J/kg⋅°C
C.) Copper, 390 J/kg⋅°C A.)Steel, 450 J/kg⋅°C B.)Aluminum, 910 J/kg⋅°C
The precise volume of water in a beaker depends on the temperature of the water. Rank from greatest to least the volumes of water at these A.)0°C B.)4°C C.)10°C
C.)10°C A.)0°C B.)4°C
What is evaporation?
Change of phase from liquid to gas
True or false? Temperature is a measure of the total kinetic energy in a substance.
False. Temperature is a measure of the average (not total!) translational kinetic energy of molecules in a substance. For example, there is twice as much total molecular kinetic energy in 2 L of boiling water as in 1 L—but the temperatures of the two volumes of water are the same because the average translational kinetic energy per molecule is the same in each.
What is the explanation for feather beds being warm?
Feathers (and the air they trap) are good insulators and thus conduct body heat very slowly to the surroundings.
How is the energy value of foods determined?
Food is burned and then the energy released is measured.
Why doesn't water freeze at 0°C when foreign ions are present?
Forgeign ions decrease the number of water molecules at the interface between ice and water where freezing occurs.
How does glass act like a one-way valve for a conventional greenhouse? Does the atmosphere similarly act as a one-way valve?
Glass allows high frequency infrared radiated energy in, but prevents energy from going out. Likewise for the atmosphere acting as one-way valve
In which direction does internal energy flow between hot and cold objects?
Heat goes from hottest to coldest.
How does heat differ from internal energy, or are they two terms for the same thing?
Heat is internal energy that flows from hot to cold locations. They are not two terms for the same thing.
Relatively speaking, do high-frequency waves have long wavelengths or short wavelengths?
High frequency waves have shorter wavelengths.
You can hold your fingers beside the candle flame without harm, but not above the flame. Why?
Hot air travels upward by air convection. Since air is a poor conductor, very little heat travels sideways to your fingers.
Distinguish between humidity and relative humidity.
Humidity is a measure of how much water vapor is in the air. Relative humidity is the ratio of how much water is in the air to the largest amount of water vapor the air can hold.
Use Equation: ΔL=ΔαΔT Consider a bar 1 m long that expands 0.6 cm when heated. Show that when similarly heated, a 100-m bar of the same material becomes 100.6 m long.
If a 1-m long bar expands 0.6 cm when heated, then the bar of the same material that is 100 times as long will expand 100 times as much: 0.6 cm for each meter, or 60 cm or about 2 feet.
If a good absorber of radiant energy were a poor emitter, how would its temperature compare with the temperature of its surroundings?
If a good absorber were not also a good emitter, there would be a net absorption of radiant energy and the temperature of the absorber would remain higher than the temperature of the surroundings. Things around us approach a common temperature only because good absorbers are, by their very nature, also good emitters.
How much energy is in a nut? Burn it and find out. The heat from the flame is energy released when carbon and hydrogen in the nut combine with oxygen in the air (oxidation reactions) to produce CO2 and H2O. Pierce a nut (pecan or walnut halves work best) with a bent paper clip that holds the nut above the table surface. Above this, secure a can of water so that you can measure its temperature change when the nut burns. Use about 103 cm (10 mL) of water and a Celsius thermometer. As soon as you ignite the nut with a match, place the can of water above it and record the increase in water temperature once the flame burns out. The number of calories released by the burning nut can be calculated by the formula Q=cmΔT, where c is its specific heat (1 cal/g⋅°C), m is the mass of water, and ΔT is the change in temperature. The energy in food is expressed in terms of the Calorie, which is 1000 of the calories you'll measure. So to find the number of Calories, divide your result by 1000. (See Think and Solve #36.)
If you use a o.6 gram peanut, your value should be about 1,400 calories, assuming all the heat energy went into the water.
When the temperature of ice-cold water is increased slightly, does it undergo a net expansion or a net contraction?
It contracts with decreasing temperature until 4 degrees Celsius.
Suppose you apply a flame to 1 L of water for a certain time and its temperature rises by 2°C. If you apply the same flame for the same time to 2 L of water, by how much will its temperature rise?
Its temperature will rise by only 1°C because there are twice as many molecules in 2 L of water, and each molecule receives only half as much energy on average.
Since a hot cup of tea loses heat more rapidly than a lukewarm cup of tea, is it correct to say that a hot cup of tea will cool to room temperature before a lukewarm cup of tea will?
No! Although the rate of cooling is greater for the hotter cup, it has farther to cool to reach thermal equilibrium. The extra time is equal to the time it takes to cool to the initial temperature of the lukewarm cup of tea. Cooling rate and cooling time are not the same thing.
Since boiling is a cooling process, would it be a good idea to cool your hot and sticky hands by dipping them into boiling water?
No, no, no! When we say that boiling is a cooling process, we mean that the water (not your hands!) is being cooled relative to the higher temperature it would attain otherwise. Because of cooling, it remains at 100°C instead of getting hotter. A dip in 100°C water would be a big ouch!
Does a common electric fan cool the air in a room? If not, then why is it used in an overly warm room?
No. A fan does not cool the room, but instead promotes the evaporation of perspiration, which cools the body.
Would evaporation be a cooling process if molecules of every speed had an equal chance to escape from the liquid surface?
No. If molecules of all speeds escaped equally easily from the surface, the molecules left behind would have the same range of speeds as before any escaped, and there would be no change in the liquid's temperature. When only the faster molecules can break free, those that remain are slower and the liquid becomes cooler.
If the water level in a dish of water remains unchanged from one day to the next, can you conclude that no evaporation or condensation has occurred?
Not at all, because a lot of activity is taking place at the molecular level. Both evaporation and condensation occur continuously. The constant water level simply indicates equal rates of both, not that nothing's happening. When just as many molecules evaporate as condense, no net evaporation or condensation occurs. The two processes cancel each other.
How much energy is transferred when 1 g of boiling water at 100°C cools to ice water at 0°C?
One gram of boiling water transfers 100 calories when it cools 100°C to become ice water.
How much energy is transferred when 1 g of ice water at 0°C freezes to ice at 0°C?
One gram of ice water at 0°C transfers 80 calories to become ice at 0°C.
How much energy is transferred when 1 g of steam at 100°C condenses to water at 100°C?
One gram of steam at 100°C transfers 540 calories of energy when it condenses to become water at the same temperature.
How much energy is transferred when 1 g of steam at 100°C turns into ice at 0°C?
One gram of steam at 100°C transfers to the surroundings a grand total of the above values, 720 calories, to become ice at 0°C.
What is sublimation?
Phase change from solid directly to gaseous phase.
An object that radiates energy at night is in contact with the relatively warm Earth. How does poor conductivity affect the object's temperature relative to air temperature?
Poor conductivity means there is little heat from the ground and the object can cool by radiation to temperatures below that of the surrounding air temperature.
In lab you submerge 100 g of 40°C iron nails in 100 g of 20°C water (the specific heat of iron is 0.11 cal/g?°C.) (a) Equate the heat gained by the water to the heat lost by the nails, and show that the final temperature of the water becomes 22°C. (b) Your lab partner is surprised by the result and says that since the masses of iron and water are equal, the final water temperature should be closer to 30°C, halfway between. What is your explanation?
Q gained by water = Q lost by nails, so (mcΔT)water = (mcΔT)nails: (100g)(1.0 g* ºC)(T - 20ºC) = (100g)(0.11g* ºC)(40ºC - T), where T = 22ºC. Although the masses are the same, the specific heats are widely apart, iron being very low and water incredibly high. It takes as much heat as the iron can release to raise water by about 2ºC.
What is terrestrial radiation?
Radiation emitted from Earth's surface.
Why do fish benefit from water being most dense at 4°C?
Since water is most dense at 4°C, colder water rises and freezes on the surface, which means that fish remain in relative warmth!
What eventually happens to the solar energy that falls on Earth?
Sooner or later, it will be radiated back into space. Energy is always in transit—you can rent it, but you can't own it.
Why is a steam burn more damaging than a burn from boiling water at the same temperature?
Steam contains more energy than boiling water at the same temperature.
Why is it advisable to allow telephone lines to sag when stringing them between poles in summer?
Telephone lines are longer in summer, when they are warmer, and shorter in winter, when they are cooler. They therefore sag more on hot summer days than in winter. If the telephone lines are not strung with enough sag in summer, they might contract too much and snap during the winter.
Since all objects emit energy to their surroundings, why don't the temperatures of all objects continuously decrease?
Temperatures don't continuously decrease because all objects are also absorbing radiant energy.
If 70°F air feels warm and comfortable to us, why does swimming in 70°F water feel cool?
The 70º C feels good because the air is a poor conductor. Water is a better conductor and so our bodies transfer the heat quicker the water than the air. Thus, we feel 70º C water pretty cold.
An iron thumbtack and a big iron bolt are removed from a hot oven. Both are red-hot and have the same temperature. When dropped into identical containers of water of equal temperature, which one raises the water temperature more?
The big iron bolt has more internal energy to impart to the water and warms it more than the thumbtack. Although both objects have the same initial temperature (the same average kinetic energy per molecule), the more massive bolt has more molecules and therefore more total energy—internal energy. This example underscores the difference between temperature and internal energy.
Why doesn't a wire simply cut a block of ice in two when it passes through the ice?
The block doesn't separate because the water above the wire refreezes when pressure on it is reduced.
When H2O in the vapor phase condenses, is the surrounding air warmed or cooled?
The change of phase is from vapor to liquid, which releases energy (see Figure 17.17), so the surrounding air is warmed. Look back to Figure 17.8 for another way to see this. The H2O molecules that condense from the air are the slower ones. Their removal raises the average kinetic energy of the remaining molecules—hence the warming. This goes hand in hand with water cooling when faster-moving molecules evaporate—where the ones that remain in the liquid phase have a lowered average kinetic energy.
In a 25°C room, hot coffee in a vacuum flask cools from 75°C to 50°C in 8 hours. Explain why your prediction is that its temperature after another 8 hours will be 37.5°C.
The coffee decreases 25 º Cin temperature in 8 hours. Newton's law of cooling tells us that its rate of cooling is proportional to the temperature difference. So, when the temperature difference is half as great, the rate of cooling is half as great. Hence, the coffee will lose 12.5 º C in another 8 hours, half as much as in the first 8 hours
Heat
The energy that flows from a substance of higher temperature to a substance of lower temperature, commonly measured in calories or joules.
Is it the boiling of water or the higher temperature of water that cooks food faster in a pressure cooker?
The higher temperature, not boiling, cooks food faster.
Absolute Zero
The lowest possible temperature that a substance may have—the temperature at which molecules of the substance have their minimum kinetic energy.
Under what conditions can we say that "a thermometer measures its own temperature"?
The necessary condition is thermal equilibrium; only then will the thermometer and the substance being measured have the same temperature.
Specific Heat Capacity
The quantity of heat per unit mass required to raise the temperature of a substance by 1 Celsius degree.
Suppose that 4 g of boiling water is poured onto a cold surface and 1 g rapidly evaporates. If evaporation takes 540 calories from the remaining 3 g of water and no other heat transfer takes place, what will be the temperature of the remaining 3 g?
The remaining 3 g will turn to 0°C ice. 540 calories from 3 g means each gram gives up 180 calories. 100 calories from a gram of boiling water reduces its temperature to 0°C, and the removal of 80 more calories turns it to ice. This is why hot water so quickly turns to ice in a freezing-cold environment. (In practice, because of other heat transfer, more than 1 g of the original 4 g would need to evaporate to freeze the rest.)
At what temperature do the combined effects of contraction and expansion produce the smallest volume for water?
The smallest volume of water (and the densest) occurs when water is at 4 degrees Celsius.
How are the speeds of molecules of air affected as they separate from one another when escaping from the nozzle of a party balloon?
The speeds are decreased with expansion.
Internal Energy
The total of all molecular energies, kinetic plus potential, that are internal to a substance.
A farmer turns on the propane burner in his barn on a cold morning and heats the air to 20°C (68°F). Why does he still feel cold?
The walls of the barn are still cold. The farmer radiates more energy to the walls than the walls radiate back, and he is chilled. (Inside your home or your classroom, you are comfortable only if the walls are warm, not just the air.)
When you step out of a swimming pool on a hot, dry day in the Southwest, you feel quite chilly. Why?
The water from your skin is evaporated quickly which has a cooling effect on the skin and thus, making the person cold.
Wrap a piece of paper around a thick metal bar and place it in a flame. Notice that the paper will not catch fire. Can you explain this in terms of the conductivity of the metal bar? (Paper generally will not ignite until its temperature reaches about 230°C.)
This activity nicely shows that metal is a good conductor of heat. Paper in a flame by itself easily reaches ignition temperature and catches on fire. But this ignition temperature isn't reached when the paper is wrapped around a thick metal bar that absorbs energy from the flame, which is then not absorbed by the paper.
In a still room, smoke from a candle will sometimes rise only so far, not reaching the ceiling. Explain why.
This is because hot air expands and thus becomes less dense and rises up until the density is matched up with the buoyant force acting on the air.
When two cups of hot chocolate, one at 50°C and the other at 60°C, are poured into a bowl, why will the temperature of the mixture be between 50°C and 60°C?
This is because one temperature increases and the other decreases until thermal equilibrium is reached.
Why does the pupil of the eye appear black?
This is because the light that enters the eye usually doesn't exit. With the flash turned on, however, some light does.
What does it mean to say that the greenhouse effect is like a one-way valve?
Transparent material—atmosphere for Earth and glass for the greenhouse— allows only incoming short wavelengths and blocks outgoing long wavelengths. As a result, radiant energy is trapped within the "greenhouse."
What are the temperatures for freezing water on the Celsius and Fahrenheit scales? For boiling water?
Water freezes at 0 degrees Celsius or 32 degrees Fahrenheit, and boils at 100 degrees Celsius or 212 degrees Fahrenheit.
Which has a higher specific heat capacity: water or sand?
Water has a higher specific heat capacity. Water has greater thermal inertia and takes a longer time to warm in the hot sunlight and a longer time to cool on a cold night. Sand has a low specific heat capacity, as evidenced by how quickly the surface warms in the morning sunlight and how quickly it cools at night. (Walking or running barefoot across scorching sand in the daytime is a much different experience than walking on cool sand in the evening.)
Why is the temperature fairly constant for landmasses surrounded by large bodies of water?
Water has a moderating effect- slow to warm and slow to cool.
Why does dew form on the surface of a cold soft-drink can?
Water vapor in the warm air is chilled when it makes contact with the cold can. What is the fate of chilled water molecules? They are slower when they collide, and they stick. This is condensation, which is why the surface of a cold can is wet.
Why does blowing over hot soup cool the soup?
We increase the net evaporation and its cooling effect by removing the warm vapor that tends to condense and reduce net evaporation.
When an air molecule is hit by an approaching faster-moving molecule, does its rebound speed increase or decrease? How about when it hits a receding molecule?
When the air molecule is hit by faster moving molecules the rebound seed increases. When it hits a receding molecule its rebound speed decreases.
Why can you place your hand briefly inside a hot oven without harm, but you are burned if you touch the metal sides of the oven?
When your hand is in the air of the hot oven, you're not harmed mainly because air is a poor conductor—heat doesn't travel well between the hot air and your hand. Touching the hot metal sides of the oven is another story because metal is an excellent conductor and considerable heat flows into your hand.
When will water boil at a temperature lower than 100°C?
Where the air pressure is reduced.
Explain why a firewalker can step quickly without harm on red-hot coals with bare feet.
Wood is a good insulator even when it's hot; therefore very little thermal energy is transferred to the feet.
If you add the same quantity of heat to both a 1-L and a 2-L container of water, compared with the temperature change of water in the smaller container, the temperature change of water in the larger container will be a.half. b.more than half but less than twice. c.twice. d.none at all.
a.half.
The greatest expansion of water occurs when a.it turns to ice. b.at 4°C when it gains temperature. c.at 4°C when it loses temperature. d.None of these.
a.it turns to ice.
Hot sand cools off faster at night than plants and vegetation, which indicates that the specific heat capacity for sand is a.less than that of plants. b.more than that of plants. c.likely the same as that of plants. d.Not enough information to answer.
a.less than that of plants.
Whether one object is warmer than another has most to do with a.molecular kinetic energy. b.molecular potential energy. c.heat flow. d.masses of internal particles.
a.molecular kinetic energy.
The fact that gasoline will overflow from an automobile tank on a hot day is evidence that the expansion of gasoline is a.more than the tank material. b.about the same as the tank material. c.less than the tank material. d.negligible.
a.more than the tank material.
The motion of molecules that most affects temperature is a.translational motion. b.rotational motion. c.internal vibrational motion. d.simple harmonic motion.
a.translational motion.
The specific heat capacity for aluminum is more than twice that of copper. If equal quantities of heat are given to equal masses of aluminum and copper, the metal that more rapidly increases in temperature is a.aluminum. b.copper. c.Actually both will increase at the same rate. d.None of these.
b.copper. Explanation: The material with the least specific heat capacity has the least "thermal inertia" and changes the most.
Matter does not contain a.internal energy. b.heat. c.It contains both. d.It contains neither.
b.heat. Explanation: By definition, heat is the internal energy that transfers due to a temperature difference, not the internal energy itself.
When heat is added to a system, the temperature of the system a.rises. b.may or may not rise. c.falls. d.may or may not fall.
b.may or may not rise. Explanation: The first answer is correct only if the substance doesn't change phase. Adding heat to a cube of 0° ice, for example, doesn't raise its temperature.
At absolute zero, a substance has a.absolutely no molecular motion. b.no more energy to give up. c.no volume. d.All of these.
b.no more energy to give up.
Absolute zero corresponds to a temperature of a.0 K. b.-273° C c.Both of these. d.None of these.
c.Both of these.
Internal energy is normally measured in units of a.calories. b.joules. c.Both of these. d.None of these.
c.Both of these. Explanation: Calories and joules, like miles and meters, are different units for the same thing; 1 calorie = 4.18 joules.
Water at 4°C will expand when it is slightly a.cooled. b.warmed. c.Both. d.Neither.
c.Both.
The thermal expansion of steel is about the same as for a.water. b.air. c.concrete. d.All of these.
c.concrete. Explanation: This fact is important to civil engineers in the construction of concrete that is reinforced with steel rods.
Heat is simply another word for a.temperature. b.thermal energy. c.internal energy that flows from hot to cold. d.radiant energy.
c.internal energy that flows from hot to cold.
Calculate the quantity of heat absorbed by 20 g of water that warms from 30°C to 90°C. (Use Quantity of heat:Q=cmΔT or q=mcΔT).
q=mcΔT = (20g)(1 cal/g*ºC)(90ºC - 30ºC) = 1,200 Cal
Use the formula (q=mcΔt) to show that 3000 cal are required to raise the temperature of 300 g of water from 20°C to 30°C. For the specific heat capacity c, use 1 cal/g⋅°C.
q=mcΔt (300 g)(1 cal/g * degrees Celsius)(30 degrees Celsius - 22 degrees Celsius) = 300 cal
