L>Homework options Ch 13-14

Chapter13 , Chapter14

Chapter 13

Questions:

2) as soon as a mercury thermometer is warmed, the mercury expands. What happens when the mercury expands? Do an ext molecules the mercury appear or walk the distance between molecules increase?Answer: Clearly there is no new mercury included or lost to the sealed thermometer. The mercury expands because the atoms are additional apart from each other. This method they room not together tightly packed and also that the density has gained smaller.

You are watching: A liter of hot water will cool to room temperature faster in a

3) Why is the sometimes much easier to eliminate the lid from a tightly closeup of the door jar after ~ warming the under hot running water?

Answer: commonly when ingredient food is sealed in jars, that is sealed if hot. When the seasoned cools, and also the air above the ingredient cools, the pressure of the air decreases. By heater the jar, the air above the ingredient in the jug is heated and also will raise the press slightly, making it closer come atmospheric pressure and easier come open.

4) A closed bottle placed in a fire will all of sudden explode. Why?

Answer: together the gas in the party heats up in the closed bottle, the pressure will rise. Once the press is much more than the bottle can hold, it will explode.

5) on the average, top top a warm day carry out you think the wait molecules room closer together, furthermore apart, or the exact same distance apart together on a cold day? Assume that atmospheric push is the exact same on both days.

Answer: The air molecules will certainly be more apart ~ above the warm day. When a gas is heated, the will shot to expand, and make the thickness lower, so that the molecule are more apart.

6) A cuircular ring is heated native 20 °C come 80 °C. Will the hole in the ring end up being larger or smaller?

Answer: The hole will come to be larger. Mental the demonstration with the aluminum ball and ring i did in class. Another way to think around it is come imagine cut the ring and bending that out into a straight item of metal. When the straight metal bar is heated, that will expand in length. Currently bend it ago into a circular ring. The one has acquired larger, so the radius that the hole must have as well.

12) If the temperature that a gas is increased from 20 °C to 100 °C, by what aspect does the kinetic power of the molecule increase?

Answer: convert the temperature to Kelvin, 20 °C = 293K and 100 °C = 373K. The temperature has actually increased by a variable of

*
. The rise in kinetic power will it is in the same factor, because the kinetic energy of the molecule is straight proportional to temperature.

Exercises:

1) Room temperature is often defined as 68 °F. What temperature is this on the Celsius scale? on the absolute scale?

Answer: utilizing the formula

*
we discover
*
. Top top the absolute scale, us just add 273K come the °C, so that this is
*
.

2) top top a warm day it is 90 °F outside. What is this in degrees Celsius?

Answer:

*

9) If a gas is compressed come one-fifth its original volume however the temperature is maintained constant, what happens to the pressure?

Answer: indigenous Boyle"s law we know that

*
. If the volume is one-fifth as huge as it to be originally, then the pressure need to be 5 times together big. This is since five times one-fifth equals one, or
*
, keeping the product PV constant.

11) If the pressure on a gas is tripled, what happens to the volume if the temperature is maintained constant?

Answer: together in the vault problem, in bespeak to save the product PV constant, the volume must be one-third its initial volume.

12) The temperature the a gas in a glass container is raised from 300K to 600K. Just how does the push change?

Answer: since the temperature are already in K, us can directly calculate the factor through which the temperature has been increased. We can easily see the the temperature has actually been doubled. In that case, indigenous Charles" Law, the pressure will additionally double.

Chapter 14

Questions:

3) Why would certainly you expect the water temperature in ~ the bottom the a waterfall to be slightly greater than at the top?

Answer: The water in the waterfall loser gravitational potential energy and gains kinetic power as the falls. As soon as it will the bottom, it collides (inelastically) v the water listed below the falls. In one inelastic collision, the mechanical energy is transformed into warmth energy, i m sorry should warm the water slightly.

5) go an electric fan cool the air? Why or why not? If not, why use it?

Answer: An electrical fan offers electricity, and also the fan motor has actually resistance, so the actually produced heat energy, heater up the air approximately it. The factor a fan have the right to cool united state off is the it brings drier air come our bodies which have the right to then carry moisture which has actually evaporated away from our bodies. The humidity carries away heat energy from ours bodies once it evaporates, cooling us off.

7) The particular heat that water is fairly large. Define why this reality makes water particularly good for heaters (that is, hot-water radiators).

Answer: due to the fact that water has actually a big specific heat, water have the right to carry huge amounts the heat. This heat have the right to be supplied to warmth a the majority of air and also make rooms warm.

8) Why walk water in a canteen remain cooler if the towel jacket bordering the canteen is retained moist?

Answer: The water evaporating indigenous the canteen requires thermal energy to turn into a gas and also it gets part of this power from the canteen, keeping it cool.

10) Why perform you feeling cool once you action out of a swim pool right into a warmth breeze?

Answer:The water evaporating native our body requiers thermal power to end up being a gas, so that gets component of that power from us, cooling united state off.

12) as soon as your human body overheats, it perspires. What is the worth of the process?

Answer: In order to evaporate, the perspiration requires a large amount of thermal power . This thermal energy is take away from ours bodies and also cools united state off. As long as friend have enough fluid in your body, this process can continue and will keep your human body temperature.

15) describe why skin burns led to by heavy steam are frequently so severe.

Answer: In bespeak to come to be steam, every gram that water had actually to absorb 540 calorie of warm energy. Once the vapor contacts your skin (which is a reasonably cool 37°C ) it condenses and also releases this heat energy to her skin. The an ext steam that touches your skin, the much more serious the burn will be.

16) will certainly potatoes chef faster if the water is boiling faster?

Answer: No. The temperature the the cook water deserve to never get over 100°C, and the temperature identify the rate with i beg your pardon food cooks. The extra energy from the high flame goes into creating steam, not into cooking the potatoe.

21) in ~ the same temperature, why walk a tile floor it seems ~ so lot cooler to your bare feet than a carpet?

Answer: The tile is a much far better heat conductor 보다 carpet. When your skin contact the tile, warmth will it is in readily carried out away indigenous you; you feel cool. As soon as your feet call carpet, i m sorry is a negative thermal conductor, very small heat flows away from you; you feel warm.

25) Why perform Bedouins wear numerous layers of apparel in the desert also when the temperature will 50°C (122°F)?

Answer: The class of apparel trap air in between them and air is a very good thermal insulator (poor thermal conductor). This keeps the bedouins cool even on the hottest day.

28) Why does the earth cool at night an ext quickly when the sky is clear than once it is cloudy?

Answer: The clouds act together an insulating layer and reflect heat radiation ago to the earth as well as keep wait from convecting openly upward.

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30) Why does dirty eye melt faster than clean snow?

Answer: The dirty snow, i m sorry is darker, is more efficient at absorbing the suns radiation 보다 clean snow. This energy can then be used to heat the snow and melt it.

Exercises:

1) how much warm (joules) is compelled to progressive the temperature that 2.0kg of water from 0°C come 20°C? (for instance when a two-liter party of water warms to room temperature from near freezing)

Answer: The heat power required to raise the water temperature is

*
. The starting temperature is
*
, and the last temperature is
*
. The particular heat the water is
*
, which means it takes 4180J that heat energy to advanced the temperature the 1kg the water by 1°C. The heat power needed to warmth the water is then:
*

3) exactly how much work have to a human do to balance out eating a 400 Cal piece of cake?

Answer: The food unit of energy is the Cal which is indistinguishable to the kcal, so

*
. That means a human must do a full work that
*
. This is the exact same amount of work expended by an 84kg man as he climbs an around 2000m mountain!