Assignment 9: Temperature and Heat

At what temperature do the combined effects of contraction and expansion produce the smallest volume for water?

4°C

Water is most dense at ___________.

4°C

Which one of these is largest amount of energy?

1 Calorie

Does a substance that cools off quickly have a high or a low specific heat capacity?

A low specific heat capacity

Which is the largest unit of heat transfer-Calorie, calorie, or joule?

Calorie

Thermal conduction mostly involves the motion of _________.

Electrons

What happens when Dr. Hewitt heats up the strip?

It bends

Which of these has the highest specific heat capacity?

Water

Which one of these cites the lowest temperature?

270 K

What are the temperatures for freezing water and boiling water on the Kelvin temperature scale?

273 K, 373 K

Why do substances expand when their temperature is increased?

Higher-temperature substances have greater molecular motion.

How does using a pressure cooker affect the amount of internal energy in the water inside the pressure cooker, and why?

It increases the amount of internal energy because it does not allow the heat to boil the water.

Ceiling fans can make you feel cooler in a warm room. Do ceiling fans reduce room temperature?

No

What would be the consequence of completely eliminating the greenhouse effect?

The average temperature on the surface of Earth would drop to -18°C.

Distinguish between a calorie and a joule.

1 calorie = 4.19 joules

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

Absorb, release

Distinguish between weather and climate.

Climate is what you expect, whereas weather is what you get.

When air rapidly expands, its temperature normally _________.

Decreases

Distinguish between evaporation and boiling.

Evaporation happens at a liquid surface, whereas boiling occurs in the bulk of the liquid.

Why doesn't water freeze at 0°C when foreign molecules or ions are present?

Foreign molecules or ions get between water molecules and ice crystals, thus impeding crystal formation.

What is the role of "loose" electrons in heat conductors?

Free electrons can move through a material carrying heat, jostling atoms and other electrons.

How does glass act like a one-way valve for a conventional greenhouse? Does the atmosphere similarly act as a one-way valve?

Glass transmits solar radiation into the greenhouse and blocks infrared radiation from leaving the greenhouse. The same thing happens in the atmosphere.

Does a good insulator prevent heat from escaping or slow its passage?

Insulators slow the passage of heat.

What happens to the temperature of something that radiates energy without absorbing the same amount in return?

It cools

What happens to water at room temperature if you decrease the atmospheric pressure around it?

It will first boil and then freeze.

Why does the pupil of the eye appear black?

Light that enters the pupil bounces several times before exiting, and is absorbed on each bounce, so little light exits.

If you touch the metal sides in an oven with your bare hand, you're in trouble. But hold your hand briefly in the oven air and you're okay. What does this tell you about the relative conductivities of metal and air?

Metal is a good conductor of heat, whereas air is a terrible conductor of heat.

What is terrestrial radiation?

Terrestrial radiation is infrared radiation emitted by Earth's surface.

How is the energy value of foods determined?

The food is burned and the energy released is measured.

Why is the temperature fairly constant for landmasses surrounded by large bodies of water?

Water has a high specific heat capacity.

What kind of strip is Dr. Hewitt holding in his hand?

a strip consisting of brass on one side and steel on the other, welded together This is called a bimetallic strip

When we speak about heat we refer to ___________.

energy in transit

In what way did the Industrial Era contribute to climate change? Discuss better uses of fossil fuels than creating heat and smoke. In the Industrial Era the large-scale burning of fossil fuels caused the __1____ of amount of greenhouse gases in the atmosphere that resulted in climate change. Apart from burning fossil fuels to produce energy, ___2_ of fossil fuels.

1. Increase 2. Many modern materials are made

In an insulated container, 0.800 kg of water at 40.0∘C is mixed with 0.500 kg of ice at −15.0∘C. Find the final temperature Tf of the system. The freezing point of water is 0∘C. Express your answer in degrees Celsius.

0 ∘C

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?

1 calorie, 80 calories, 540 calories

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

As water rushes out, the pressure on the remaining water is reduced, so the water boils.

You are mixing water with ice in an insulated container. The following are given: the amount of heat absorbed by the ice if heated to its melting point: 400 J, the amount of heat absorbed by the ice if it all melts (which includes the heat needed to bring the ice to its melting point): 2100 J, the amount of heat given off by the water if cooled to its freezing point: 1800 J, and the amount of heat given off by the water if it all freezes (which includes the heat needed to bring the water to its freezing point): 5200 J. Based on this information, at equilibrium, which phases are present?

Both ice and water Since 2100 J is more than 1800 J, the ice would not completely melt by the time the water reaches its freezing point. However, since 400 J is less than 1800 J, the ice will, indeed, melt partially. The final temperature of the mix is 0∘C.

Rank the boiling-water temperatures in different locations. Rank from largest to smallest. To rank items as equivalent, overlap them.

Death valley Sea level Denver Co.

What are the temperatures for freezing water on the Celsius and Fahrenheit scales? For boiling water?

Freezing: 0°C, 32°F; boiling: 100°C, 212°F

Rank the energies needed for different phase changes for equal amounts of H2O.

From boiling water to steam From ice water to boiling water From ice to ice water

In which direction does heat flow spontaneously between hot and cold objects?

From high temperature to low temperature

What is meant when we say that a thermometer is in thermal equilibrium with another object?

Heat no longer flows between the object and thermometer when both are at the same temperature.

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

Rising air expands and cools. Water drops condense when moist air cools.

What is sublimation? Is it a heating or cooling process?

Sublimation is when the fastest molecules at the surface of a solid have escape velocity and leave to become a gas. It leaves behind the slower, cooler molecules.

How would increasing the density of air in the atmosphere affect the amount of infrared radiation returned by the atmosphere back toward Earth?

The amount of infrared radiation would increase.

What happens to the amount of "microscopic slush" in cold water when its temperature is increased?

The amount of microscopic slush decreases as the temperature increases.

According to the law of conservation of energy, if ocean water cools, then something else should warm. What is it that warms?

The cooling ocean warms the air.

What does a windchill of -20°C mean?

The cooling rate will be the same as if the temperature were -20°C without wind.

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

The steam releases considerable energy when it condenses to liquid on the skin.

What happens when you heat water that is at 0∘C?

The temperature increases until it reaches 100

What happens when you heat ice that is at 0∘C?

The temperature stays constant until all the ice is melted.

What happens when you heat water that is at 100∘C?

The temperature stays constant until all the water is boiled.

Water with a mass of 0.500 kg at 15.0∘C is mixed with 0.800 kg of water at 35.0∘C. What is the final temperature Tf of the mixture?

m1 = 0.8 kg T1 = 35 C m2 = 0.5 kg T2 = 15 C T = (cw m1T1 + cw m2T2) / (cw m2 + cwm1) final temperature: T = 27.31 C

Melting and freezing are _________.

opposite processes

The purpose of a pressure cooker is to _________

prevent cooling from occurring

Heat travels from the Sun to Earth by the process of _________.

radiation

What do you use a pressure cooker for?

to prevent boiling and cooling

Most energy transfer occurs in water when it _________.

vaporizes

In an insulated vessel, a quantity of hot water at temperature T1 is mixed with a different quantity of cold water at temperature T2. After equilibrium is established, the vessel contains __________.

water only

What type of gas absorbs and re-emits infrared radiation?

greenhouse gases

Which will normally warm faster: a black pot of cold water or a silvered pot of cold water? Which will cool faster?

Black, Black

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

Boiling is a cooling process, so energy is removed as quickly as it is added.

Why does the strip behave as it does when Dr. Hewitt heats it up?

Both metals expand unequally.

In an insulated container, 0.50 kg of water at 80∘C is mixed with 0.050 kg of ice at −5.0∘C. After a while, all the ice melts, leaving only the water. Find the final temperature Tf of the water. The freezing point of water is 0∘C.

Change in the temperature of cold water dT = Tf-0 C = Tf Change in the temperature of original water in the container dT' = 80-Tf Latent heat of melting of ice L = 80cal/g Specific heat of water C = 1cal/g C Heat absorbed by ice to melt = mass(mi) x latent heat(L) Heat absorbed by water = mass(mw) x specific heat(C) x change in temperature (dT') mi=0.050kg= 50g and mw=0.50kg = 500g So, heat absorbed by the ice + heat absorbed by cold water = heat lost by hot water( at 80 C) mi*L + mi*CdT = mw*CdT' 50*80 + 50*1*(Tf) = 500 * 1 * (80-Tf) Cancelling out 50 from each term, 80+Tf=800- 10Tf So 11Tf =720 Tf = 65.45 C

What is condensation? Is condensation a warming or cooling process?

Condensation is when a gas becomes a liquid. It is a warming process.

When the temperature of ice-cold water is increased slightly, does it undergo a net expansion or a net contraction?

Contraction

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

Cool air contains more slow water molecules, which stick together more often when they collide.

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. Steel, 450 Aluminum, 910 Copper, 390 Rank from fastest to slowest. To rank items as equivalent, overlap them

Copper Steel Aluminum

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

Hot coals have a low conductivity, and water on wet feet absorbs a lot of energy as it vaporizes.

Distinguish between humidity and relative humidity.

Humidity is the mass of water per unit volume. Relative humidity is the ratio of the amount of water in the air to the maximum amount of water the air could contain.

Why is ice less dense than water?

Ice crystallizes with an open structure, and the gaps that form between the water molecules in ice increase its volume.

When an air molecule is hit by an approaching, faster moving molecule, does the approaching molecule's rebound speed increase or decrease? How about when it hits a receding molecule?

Increase, decrease

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

Increase. Higher pressure collapses the bubbles that form.

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

Pressure beneath the wire melts the ice without warming it, so the liquid flows above the wire, where it refreezes at lower pressure.

Show that 2000 cal are required to increase the temperature of 20 g of water from 0∘C to 100∘C. The specific heat capacity for water is 1 cal/(g⋅∘C).

Q=cmΔT=(1cal/(g⋅∘C))⋅(20g)⋅(100∘C)=2000cal

Relatively speaking, do high-frequency waves have long wavelengths or short wavelengths? Name an electromagnetic wave with higher frequency than blue light.

Short, ultraviolet

Cite a primary difference between waves of solar radiation and waves of terrestrial radiation.

Solar radiation peaks at shorter wavelengths in the visible, whereas terrestrial radiation peaks at longer wavelengths in the infrared.

What are the four common phases of matter?

Solid, liquid, gas, plasma

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

Some are slow and some are fast.

How are the speeds of molecules of air affected when the air is compressed by the action of a tire pump? What happens to the temperature of the air?

Speeds increase; temperature increases.

How would decreasing the percentage of greenhouse gases affect the amount of infrared radiation reflected by the atmosphere back toward Earth?

The amount of infrared radiation would decrease.

Why isn't Millie's hand burned when she holds it above the escape valve of the pressure cooker (see Figure 16.8 in the textbook)?

The escaping gas is cooled by expansion.

How does the pressure exerted by bubbles in the water compare with the atmospheric pressure when the temperature of water in an open pressure cooker is below 100

The pressure exerted by the bubbles is less than the atmospheric pressure below 100∘ C and equals the atmospheric pressure at 100∘ C.

What happens when you heat ice that is at -40∘C?

The temperature increases until the ice reaches its melting point.

Cite three ways in which a Thermos bottle inhibits heat transfer.

There is no conduction and no convection through a vacuum, and silvered surfaces stops radiation.

In an insulated container, liquid water is mixed with ice. What can you conclude about the phases present in the container when equilibrium is established?

There is no way of knowing the phase composition without more information.

Is there a distinction between thermal energy and internal energy? Which term do physicists prefer?

Thermal energy emphasizes heat flow, whereas internal energy is the grand total of all energies inside a substance. Physicists prefer internal energy.

How is heat similar to and different from internal energy?

They are both forms of energy, but heat flows, whereas internal energy does not.

Which of the following changes would make the water balloon more likely to pop? (Ignore effects of convection within the fluid.)

Use a liquid that has a lower heat capacity than water. Use a thicker balloon Using a liquid with a lower heat capacity than water means that the candle flame will raise the liquid's temperature more quickly than for water. A thicker balloon will conduct heat through to the liquid more slowly, so that the outer part of the balloon wall will heat up more quickly to its melting point.

Which is greater-an increase in temperature of 1 Celsius degree or an increase of 1 Fahrenheit degree?

an increase of 1 °C is larger

The final temperature of the water is __________.

between T1 and T2

A thermos bottle controls heat transfer by _________.

conduction, convection, and radiation.

Newton's law of cooling applies to objects that undergo _________.

cooling or warming

You are mixing water with ice in an insulated container. The following are given: the amount of heat absorbed by the ice if heated to its melting point: 400 J, the amount of heat absorbed by the ice if it all melts (which includes the heat needed to bring the ice to its melting point): 2100 J, the amount of heat given off by the water if cooled to its freezing point: 2400 J, and the amount of heat given off by the water if it all freezes (which includes the heat needed to bring the water to its freezing point): 5200 J. Based on this information, at equilibrium, which phases are present?

Water only Since 2100 J is less than 2400 J , the ice would completely melt before the water reaches its freezing point. The final temperature of the mix is above 0∘C .

Why is evaporation a cooling process?

When the fastest molecules leave during evaporation, the slower, cooler ones remain.

You are mixing water with ice in an insulated container. The following are given: the amount of heat absorbed by the ice if heated to its melting point: 6400 J, the amount of heat absorbed by the ice if it all melts (which includes the heat needed to bring the ice to its melting point): 14,100 J, the amount of heat given off by the water if cooled to its freezing point: 1800 J, and the amount of heat given off by the water if it all freezes (which includes the heat needed to bring the water to its freezing point): 5200 J . Based on this information, at equilibrium, which phases are present?

ice only Since 6400 J is more than 5200 J, the ice would not even begin to melt by the time all the water freezes. The final temperature of the mix is below 0∘C.

Suppose that we replace the aluminum with a mystery metal and repeat the experiment in the video. As in the video, the mass of the metal is the same as that of the water. Room temperature is about 20∘C before the start of the experiment. The water heats up to 40∘C, and the mystery metal heats up to 80∘C. Compared to that of water, the heat capacity of our mystery metal is

one-third as great. Given the same input of energy, the temperature of the metal increased three times as much as the temperature of the water. Therefore, the metal has one-third the heat capacity of water. (Recall that the heat Q delivered to a substance can be written Q = mc ΔT, where m is the mass of the substance and c is its heat capacity.)