Physics Chapter 17

Heat pump

A device that transfers heat out of a cool environment and into a warm environment.

*to help evaporation occur in its mouth and bronchial tract.* Since they have no sweat glands dogs pant, this causes evaporation to occur in its mouth and bronchial tract. Since evaporation is a cooling process it cool the dogs off.

A hot dog pants -to bring more oxygen into its lungs. -to help evaporation occur in its mouth and bronchial tract. -for no particular reason - some things just happen. -to impress dogs of the opposite sex.

*even colder* Because frost occurs when water condenses on objects. And Condensation is a warming process. Excess KE of the liquid from its gas phase is transferred to the liquid when it condenses. So since no water is able to condense and produce frost, warming the objects of the continent with KE, the nights would be colder.

A substance can be sprayed on crops to prevent frost formation under many conditions. If frost did not form on the fields and woods of an entire continent, cold nights would be no different. less cold. even colder.

* raises the boiling point of water.* Since boiling is a cooling process, it causes a liquid to cool. By raising the boiling point it prevents the water from cooling a quickly, and allows the food to cook in a higher temperature.

An inventor discovers a harmless and tasteless salt, which changes its boiling point when added to water. The market value for this salt will be best if the salt raises the boiling point of water. either raises or lowers the boiling point, as the food would be cooked either way. lowers the boiling point of water.

*pressure is sufficiently lowered* lowered pressure at high altitudes decrease the boiling point of a liquid. boiling depends not only on temperature, but on pressure as well.

Boiling can occur in cold water when _______. -concentration and physics come together -sub-zero temperatures are achieved -pressure is sufficiently increased -pressure is sufficiently lowered

*below the surface and throughout water* this occurs when bubbles in the liquid form when the pressure of the vapor inside the bubbles is great enough to resist the pressure of the surrounding liquid.

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

*a transfer of energy* When a substance goes through a phase change it almost always needs to release energy, or absorb energy.

Changes of phase almost always require _______. -electron transfer -a condition of thermal equilibrium -a transfer of energy -an absence of molecular contact

*faster* glass with no ice will warm faster, water at zero Celsius will warm more quickly. Because Energy must first go into melting the ice at zero Celsius. Only when all of the ice has melted will the resulting water at zero Celsius begin to warm up.

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 slower. faster. in the same amount of time. None of the above choices are true.

*absorb energy* The is because the a liquid has a lower kinetic energy than a gas, and to change into a gas it has to absorb energy.

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

*release energy* This is because a liquid has more KE kinetic energy then a solid, and when it changes phases into a solid it has to release that energy.

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

*a warming process.* When condensation occurs excess KE, is shared with the liquid, and this increases the liquids temperature.

Evaporation is a cooling process and condensation is -a warming process. -a cooling process also. -neither a warming nor cooling process.

*the more energetic molecules are able to escape the liquid.* Molecules about to be propelled out of the liquid gain energy, while those that remain in the liquid lose energy. Thus the average kinetic energy of the molecules remaining in the liquid is lowered. Therefore cooling the liquid.

Evaporation is a cooling process because -heat is radiated during the process. -the temperature of the remaining liquid decreases. -of conduction and convection. -the more energetic molecules are able to escape the liquid. -none of these

*higher temperature* The food is able to be cooked at this higher temperature in a pressure cooker because the higher pressure of the cooker puts a pressure force on the liquid and and causes the molecules in the vapor that form the bubbles inside the boiling liquid to move at a faster rate and causes the bubbles to collapse more easily. Thus a liquid under pressure, is able to cook longer and the temperature is able to get hotter before it begins to boil.

Food in a pressure cooker is cooked faster because of the increased internal energy in the water. greater rate of bubble formation in the water. higher temperature. Choices A, B, and C are all true.

* goes up* If atmospheric pressure is raised then the molecules in the vapor that form the bubbles inside the boiling liquid need to move at a fast rate, to prevent the bubbles from collapsing. Thus if a liquid is under pressure, the liquid's temperature needs to be rise to be raise as well.

For increased atmospheric pressure, the boiling temperature of a liquid goes up. remains at 100 degrees C. goes down.

*evaporation* This is because hot water has more H2o molecules with higher KE, this causes more of them to be bumped to the surface of the liquid, and break free of the liquid in to a gas phase.

Hot water has a relatively high rate of evaporation. conductivity. convection. condensation.

*by putting it in an environment that has as little pressure on it as possible, such as a vacuum which has no atmospheric pressure*

How can you bring water to a boil without giving it any heat?

*-Both freezing point and melting point are the same for a pure substance* The melting and freezing point is the temperature in between the point at which molecules of a substance either gain KE and move apart, or lose KE and gain more molecular bonds.

How does the freezing point of a liquid compare with its melting point? -Freezing point is less than melting point for a pure substance. -Freezing point is greater than melting point for a pure substance. -Both freezing point and melting point are the same for a pure substance.

*boil the eggs for a longer time.* Since boiling not only depends on tempreture but also on pressure, the lower the atmospheric pressure, as in this case in a higher altitude, the less speed the molecules of the vapor must move to produce a bubble in a liquid

If you want to cook eggs by boiling them while in the mountains, then compared to sea-level cooking, you should use a hotter flame. boil the eggs for a longer time. boil the eggs for a shorter time. None of the above choices are true.

* prevent boiling.* If atmospheric pressure is raised then the molecules in the vapor that form the bubbles inside the boiling liquid need to move at a fast rate, to prevent the bubbles from collapsing. Thus if a liquid is under pressure, the liquid's temperature needs to be rise to be raise as well.

Increased air pressure on the surface of hot water tends to promote boiling. prevent boiling. Neither choice A nor choice B is true. Choice A and choice B are both true.

*vaporizes* In one gram of water it takes 540 cal to take water from a liqid form and vaporize it in to a gas form. It only takes 80 cal to melt it and 100cal to boil

Most energy transfer occurs in water when it _______. -vaporizes -melts -increases from its melting temperature to its boiling temperature -freezes

* a lower temperature than at sea level.* If atmospheric pressure is lowered then the molecules in the vapor that form the bubbles inside the boiling liquid don't need to move as fast to prevent the bubbles from collapsing due to the force of the lower force of atmospheric pressure. Thus, a liquid under less pressure is able to form bubbles more easily and is able to boil faster, because there is less atmospheric pressure acting on it.

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

*the saturation of cooled air* If the number of molecules returning to the layer exactly balances the number escaping, then the system is said to be at saturation, and the air is said to be saturated with water vapor

On a humid day, water condenses on the outside of a glass of ice water. This phenomenon occurs mainly because of adhesion of water molecules to glass. evaporation. the porosity of glass. the saturation of cooled air. capillary action.

Boiling

Rapid evaporation that takes place within a liquid as well as at its surface.

* the water in them contains dissolved salts and sugars*

Stored potatoes, beets, and rutabagas freeze at temperatures below zero degrees Celsius (rather than at exactly zero) because they are good radiators of energy. they are good absorbers of radiant energy. they are very dense. the water in them contains dissolved salts and sugars. All of the above choices are true.

Latent heat of vaporization

The amount of energy required to change a unit mass of a substance from liquid to gas (and vice versa).

Latent heat of fusion

The amount of energy required to change a unit mass of a substance from solid to liquid (and vice versa).

*7200* It takes 80 cals, for 1g of ice to melt, 100 cal to boil it, and 540 cals to vaporize it. so... 80*100*540=720 cal 720 cal * 10 = 7200cal

The calories needed to change 10 grams of ice at zero degrees C to steam at 100 degrees C is 6400. 7200. 6200. 8000. None of the above choices are correct.

Condensation

The change of phase from gaseous to liquid.

Evaporation

The change of phase from liquid to gaseous.

Sublimation

The change of phase from solid to gaseous, skipping the liquid phase.

*colder* Condensation occurs more in cold air, because molecules slow down, allowing them to bump into each other and form chemical bonds with each other.

The inside surface of a glass window becomes wet when the temperature outside is _______. -colder -either warmer or colder -warmer -almost exactly the same as on the inside

*a great variety of speeds.* Molecules in liquid water have wide variety of speeds. Some gain KE, while others lose KE

The molecules in a room-temperature glass of water jostle around at -a very small range of speeds. -a great variety of speeds. -much the same rates of speed.

Regelation

The process of melting under pressure and the subsequent refreezing when the pressure is removed.

* 100 calories* Because1 calorie raises 1 gram of water 1 degree. so... to raise raise 1 gram of water 2 degree would = 2 50 grams X 2 = 100

To increase the temperature of 50 grams of water by 2 Celsius degrees requires 0.04 calorie. 25 calories. 100 calories. 4.18 calories. 2 calories.

*none of these* 80 calories is absorbed to melt 1 gram, so to melt 50 grams 50*80= 4000 cal

To melt 50 grams of 0-degree-Celsius ice requires 50 calories. 25 calories. 80 calories. none of these

*more calories than are required to bring 50 grams of ice at absolute zero to the boiling point.* absolute zero is about -273, and it takes 4.187 calories for water to be raised one degree. it takes 373 degree to reach 100 C, 373*4.187= *1561.8 Cal* But ... since it take 540 cals to vaporize 1 gram of water 540*50= *27,000 cal*

To turn 50 grams of boiling water to steam requires -500 calories -more calories than are required to bring 50 grams of ice at absolute zero to the boiling point. -540 calories. -50 calories. -None of the above choices are correct.

*transfer some of their kinetic energy to us.* condensation is a warming process

We are warmed by condensation because water molecules in the air that strike our bodies -transfer some of their kinetic energy to us. -form an insulating layer on our bodies. -gain kinetic energy as they change state.

*condensing on our bodies* If condensation exceeds evaporation, you are warmed

We feel uncomfortably warm on a muggy day because water molecules are -condensing on our bodies. -evaporating and condensing on our bodies at the same rate. -evaporating from our moist bodies.

*absorbs energy from its environment.* As the ice cube melts, it absorbs heat energy from its surroundings. Water molecules frozen in the form of ice are tightly bound. Water molecules in the form of liquid aren't. So to turn a solid into a liquid means breaking bonds, and that takes energy.

When a block of ice at zero degrees Celsius melts, the ice absorbs energy and gets warmer. releases energy and gets warmer. releases energy to its environment. absorbs energy from its environment.

* does not change* When energy is added to a liquid at the boiling temperature, it converts the liquid into a gas at the same temperature. the energy added to the liquid goes into breaking the bonds between the liquid molecules without causing the temperature to change.

When heat is added to boiling water, its temperature increases. does not change. decreases.

*release energy.* This is because a liquid has more KE kinetic energy then a solid, and when it changes phases into a solid it has to release that energy.

When liquids change to a solid state, they absorb energy. release energy. neither absorb nor release energy. both absorb and release energy.

* warmer* Condensation is a warming process. Excess KE of the liquid from its gas phase is transferred to the liquid when it condenses.

When water vapor condenses on the inside of a window, the room becomes slightly warmer. cooler. neither warmer nor cooler.

*100 g of steam at 100 degrees C* this is because you don't just feel the heat of the steam, but when the steam condenses after heating wet skin, it releases high amounts of energy

Which could burn a boy scout the most? -100 g of steam at 100 degrees C -100 g of water at 100 degrees C -Both would be equally damaging.

*Due to the higher amount of water vapor in the air of NYC there is a higher amount of condensation. Since condensation exceeds evaporation it causes you *

Why is a humid summer in NYC is less comfortable than a dry summer in Tucson, AZ?