Chapter 17 Physics- Change of Phase

The calories needed to change 10 grams of ice at 0°C to steam at 100°C is

7200. This is calorie counting: 10 grams of ice to 0°C requires 10 times 80 calories = 800 calories. 10 grams of water from 0° to 100° requires (10)(100 calories) = 1000 calories. And to 100° steam is 10 (540) = 5400 calories. Add 800 + 1000 + 5400 = 7200 calories.

sublimation

A change directly from the solid to the gaseous state without becoming liquid

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

A fan does not cool the room, but instead promotes evaporation of perspiration, which cools the body. Remember blowing over your soup??

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

A liquid absorbs energy when it changes to a gas and releases energy when it changes to a solid.

What is sublimation??

A phase transition directly from a solid into the gaseous phase without first becoming a liquid. An example would be dry ice

Which molecules in a container of water are the most likely to evaporate and carry energy away with them? A. The faster ones. B. The blue ones. C. The slower ones. D. Since all have about the same speed, the ones that migrate from liquid to air.

A. The faster ones.

Near the top of a mountain, water in an open pot boils at A) a higher temperature than at sea level. B) a lower temperature than at sea level. C) the same temperature as at sea level. D) None of the above choices are true.

B) a lower temperature than at sea level.

When you step out after a hot shower, you feel cold, but you can feel warm again if you step back into the shower area. Which process is responsible for that warm feeling? A. Evaporation B. Condensation C. Both of these D. None of the above

B. condensation When you step back into the shower area, the steam that is present condenses on your body, causing it to warm up.

In a container of room-temperature water, the molecules of water A. move haphazardly, but have the same speeds at any instant. B. have a wide variety of speeds. C. move uniformly and have pretty much the same speed at any instant. D. I refuse to answer these kind of trick questions.

B. have a wide variety of speeds.

The reason that evaporation is a cooling process is A. radiation of heat during the process. B. due to conduction and convection. C. the more energetic molecules escape the liquid. D. all of the above E. none of the above

C. the more energetic molecules escape the liquid.

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

Cooling slows molecular motion until attractive forces between molecules can hold them in place.

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

Cooling sweat does not evaporate well in humid air.

In winter, why does the road surface on a bridge tend to be more icy than the road surfaces at either end of the bridge?

Either end of the bridge is in contact with the 'warm' ground

What happens to energy and temperature at the boiling point of a liquid?

Energy increases and temperature remains constant.

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

Energy is released when we change state from liquid to solid, and also the fact that the coating of ice acts as an insulating blanket. Every gram of water that freezes releases 80 calories, much of it to the fruit; the thin layer of ice then acts as an insulating blanket against further loss of heat.

what is evaporation?

Evaporation is when the fastest molecules at the surface of a liquid have escape velocity and leave to become a gas.

Why does freezing of water not occur at 0∘C when foreign ions are present?

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

Which cooks food in boiling water, high temperature or high pressure?

High temperature cooks food, not the high pressure that produces high-temperature water.

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

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

What evidence can you cite for the claim that water can boil at a temperature of 0°C? Ice forms when boiling water is added to freeze dried coffee. Ice will form in boiling water in a vacuum chamber. Ice is often seen in geysers. All of the above

Ice will form in boiling water in a vacuum chamber.

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

Increase. Higher pressure collapses the bubbles that form.

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

Increasing the temperature increases molecular vibrations until attractive forces can no longer hold the molecules in one place.

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.

a refrigerator is a heat pump. how does this work

It transfers heat out of a cold environment and into a warm environment. When the process is reversed, the heat pump is an air conditioner. In both cases, external energy operates the device.

What happens to water at room temperature if you decrease the atmospheric pressure around it? The water will immediately freeze .It will neither freeze nor boil. It will first boil and then freeze. The water will keep boiling.

It will first boil and then freeze.

Would evaporation be a cooling process if molecules of every speed had an equal chance to escape from the surface of a liquid?

No. The average kinetic energy and therefore the temperature would stay the same and no cooling would happen

Question 6:In one word, how can water in the power plant of a nuclear submarine far exceed 100°C?

Pressure The boiling point of water depends on the amount of pressure applied to its surface, as is evident in a pressure cooker. This is even more pronounced in the water of a nuclear-submarine power plant. The other choices do not explain superheating of water.

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

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

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

Steam releases more energy than boiling water of the same temperature.

Which is likely to be colder—a night when you can see the stars, or a night when you cannot?

The clear night is cooler as clouds act like a blanket and prevent radiative cooling

Which cooks food faster in a pressure cooker? The higher temperature of boiling water under pressure cooks the food faster. The higher pressure cooks the food faster. The bubbles created by boiling are full of steam that cooks the food faster. The violent convection heats and cooks the food faster.

The higher temperature of boiling water under pressure cooks the food faster.

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 ∘ C and when it equals 100 ∘ C?

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

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

The rapid evaporation of the alcohol leads to faster cooling. Therefore, the alcohol will feel cooler.

What happens when you heat water that is at 0∘∘C? The temperature does not change. The temperature increases forever. The temperature increases until it reaches 100∘∘C.

The temperature increases until it reaches 100∘∘C.

What happens when you heat ice that is at -40∘∘C? The temperature increases until the ice reaches its melting point. The temperature increases forever. The temperature stays constant.

The temperature increases until the ice reaches its melting point.

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.

When will water boil at a temperature lower than 100 degrees C ? Higher than 100 degrees celsius ?

Water boils at less than 100 degrees C when air pressure on its surface is reduced, and it boils at higher than 100 degrees C when pressure is increased.

Why does evaporation cool the liquid left behind?

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

Are melting and freezing opposite processes?

Yes, and the temperatures at which each occur are the same!

Does evaporation occur beneath the surface of water as it boils?

Yes, as evidenced by the bubbles that form. And of course, at the surface also.

Does regelation in ice involve a change of phase?

Yes. Pressure on ice crystals can crush them into a liquid. When pressure is removed, the liquid reforms to crystals in the solid phase.

Which melts faster in sunshine—dirty snow or clean snow? A. Dirty snow B. Clean snow C. Both A and B. D. None of the above.

a. dirty snow

Compared to a glass of ice water with ice in it, a glass of plain ice-cold water without ice on a warm day will warm up A. faster. B. slower. C. in the same amount of time. D. None of the above choices are true.

a. faster

A good absorber of radiation is a A. good emitter of radiation. B. poor emitter of radiation. C. good reflector. D. none of these

a. good emitter of radiation

Both black and white road surfaces radiate energy. At midnight on a starry night the warmer road surface is the A. white surface. B. black surface. C. neither, as no noticeable difference.

a. white surface

The temperature of melting ice is 32°F 0°C All of these 273 K.

all of these

Water can be brought to a boil by

applying heat and reducing air pressure on its surface

The process of evaporation occurs ____________. .at the bottom of the liquid everywhere in the liquid only within the liquid at the surface of the liquid

at the surface of the liquid

The Process of Boiling 100°C Water Tends To a) warm the water. b) cool the water. c) have no effect on the water's temperature d) All of the above

b. cool the water. When 100C water at atmospheric pressure is boiling, its temperature remains constant. That means it cools as fast as it warms.

When Steam Condenses to Water, Energy Is a) absorbed by the steam. b) released from the steam. c) conserved as the phase change occurs. d) changed to a different form.

b. released from the steam

When snow forms in the air, the surrounding air is A. None of these. B. warmed. C. both together, with no net effect. D. cooled

b. warmed

why can you wet your finger and touch a hot pan briefly ?

because energy that ordinarily would go into burning your finger goes instead into changing the phase of the moisture on your finger

Boiling is evaporation that mainly occurs _________. at the surface of water when water becomes overly hot at the bottom of a container of heated water below the surface and throughout water

below the surface and throughout water

A Thermos bottle has double glass walls with silver coating on the glass surfaces that face one another. The silver coating reduces the energy that is transferred by A. conduction. B. convection. C. radiation. D. friction. E. none of these

c. radiation

The surface of Earth loses energy to outer space due mostly to A. conduction. B. convection. C. radiation. D. radioactivity.

c. radiation

Steam burns are more damaging than burns caused by boiling water because steam has more energy per kilogram than boiling water gives up additional energy when it condenses choices A and B are both correct Choices B and C are both incorrect

choices A and B are both correct

The inside surface of a glass window becomes wet when the temperature outside is

colder

Condensation is a change of phase _________. without energy transfer from liquid to gas from gas to liquid from solid or liquid to gas

from gas to liquid

Evaporation is a change of phase _________. without energy transfer from solid or liquid to gas from gas to liquid from liquid to gas

from liquid to gas

When balls bump into one another and some gain kinetic energy, others lose the same amount of kinetic energy. Molecules about to be propelled out of the liquid are the ___, while the ___- of energy remain in the liquid

gainers; losers

The long stem of a wine glass helps to prevent

heat from the hand from warming the wine.

If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be A. lower. B. higher. C. unaffected. D. None of the above.

higher. If a good absorber were not also a good emitter, there would be a net absorption of radiant energy, and the temperature of a good absorber would continuously get hotter and hotter! (Nature does not behave that way.)

pressure cooker

holds pressurized water vapor above the water's surface, and this inhibits boiling. In this way, the boiling temperature of the water is increased to above 100°C

The purpose of a pressure cooker is to ___________. lessen pressure while cooking quicken heating lengthen the time of cooking increase the boiling temperature

increase the boiling temperature

Which contributes more to boiling, lowered temperature or pressure?

lowered pressure

Melting and freezing are

opposite processes

energy changes with change of

phase

A fire walker walking barefoot across red-hot wooden coals depends on wood's

poor conduction

Boiling can occur in cold water when

pressure is sufficiently lowered

The open structure of ________ that normally fuse at 0°C. When other kinds of molecules or ions are introduced, crystal formation is interrupted, and the freezing temperature is lowered.

pure ice crystals

why do we sweat?

regulate body temperature. sweat glands produce perspiration

When a gas is changed to a liquid, the gas

releases energy

when a gas is changed to a liquid state, the gas absorbs energy releases energy neither release nor absorbs energy both releases and absorbs energy

releases energy

Morning dew on the grass results from A. slow-moving water molecules sticking to one another. B. air pressure on water vapor. C. None of these. D. evaporation of water. E. the open-structured shape of water molecules.

slow-moving water molecules sticking to one another

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

When slow-moving water molecules collide they tend to

stick

The reason that evaporation is a cooling process is

the more energetic molecules escape the liquid. Losing the more energetic molecules in a liquid leaves the less energetic ones behind, which cools the liquid.

relative humidity

the ratio of the amount of water vapor currently in the air at a given temperature to the largest amount of water vapor the air can contain at that temperature.

The magnitudes of the energy changes during evaporation and condensation are

the same

A hot dog pants A. to help evaporation occur in its mouth and bronchial tract. B. for no particular reason, some things just seem to happen. C. to impress dogs of the opposite sex. D. to show its dominance over other dogs. E. to bring oxygen into its lungs.

to help evaporation occur in its mouth and bronchial tract

What do you use a pressure cooker for?

to prevent boiling and cooling

A refrigerator

transfers internal energy from inside to outside

Evaporation is a cooling process and condensation is

warming process. The lesson to learn is that evaporation and condensation are opposite processes, with opposite results. Evaporation warms, and condensation cools.

The statement "boiling is a cooling process" means

when a liquid is boiling, it cools as fast as it warms