14.3 Phase change and latent heat  (Page 5/9)

 Page 5 / 9

Why does snow remain on mountain slopes even when daytime temperatures are higher than the freezing temperature?

Snow is formed from ice crystals and thus is the solid phase of water. Because enormous heat is necessary for phase changes, it takes a certain amount of time for this heat to be accumulated from the air, even if the air is above $0º\text{C}$ . The warmer the air is, the faster this heat exchange occurs and the faster the snow melts.

Summary

• Most substances can exist either in solid, liquid, and gas forms, which are referred to as “phases.”
• Phase changes occur at fixed temperatures for a given substance at a given pressure, and these temperatures are called boiling and freezing (or melting) points.
• During phase changes, heat absorbed or released is given by:
$Q=\text{mL,}$

where $L$ is the latent heat coefficient.

Conceptual questions

Heat transfer can cause temperature and phase changes. What else can cause these changes?

How does the latent heat of fusion of water help slow the decrease of air temperatures, perhaps preventing temperatures from falling significantly below $\text{0ºC}$ , in the vicinity of large bodies of water?

What is the temperature of ice right after it is formed by freezing water?

If you place $\text{0ºC}$ ice into $\text{0ºC}$ water in an insulated container, what will happen? Will some ice melt, will more water freeze, or will neither take place?

What effect does condensation on a glass of ice water have on the rate at which the ice melts? Will the condensation speed up the melting process or slow it down?

In very humid climates where there are numerous bodies of water, such as in Florida, it is unusual for temperatures to rise above about $\text{35º}\text{C}\left(\text{95º}\text{F}\right)$ . In deserts, however, temperatures can rise far above this. Explain how the evaporation of water helps limit high temperatures in humid climates.

In winters, it is often warmer in San Francisco than in nearby Sacramento, 150 km inland. In summers, it is nearly always hotter in Sacramento. Explain how the bodies of water surrounding San Francisco moderate its extreme temperatures.

Putting a lid on a boiling pot greatly reduces the heat transfer necessary to keep it boiling. Explain why.

Freeze-dried foods have been dehydrated in a vacuum. During the process, the food freezes and must be heated to facilitate dehydration. Explain both how the vacuum speeds up dehydration and why the food freezes as a result.

When still air cools by radiating at night, it is unusual for temperatures to fall below the dew point. Explain why.

In a physics classroom demonstration, an instructor inflates a balloon by mouth and then cools it in liquid nitrogen. When cold, the shrunken balloon has a small amount of light blue liquid in it, as well as some snow-like crystals. As it warms up, the liquid boils, and part of the crystals sublimate, with some crystals lingering for awhile and then producing a liquid. Identify the blue liquid and the two solids in the cold balloon. Justify your identifications using data from [link] .

Problems&Exercises

How much heat transfer (in kilocalories) is required to thaw a 0.450-kg package of frozen vegetables originally at $0º\text{C}$ if their heat of fusion is the same as that of water?

35.9 kcal

a rare fraction and adjacent contraction of a sound wave are travelling in air and are separated by distance of 15cm, taken that velocity sound is 330ms what is the frequency?
Abbas
yes pls
Jennifer
Is ans 64/3
yuvraaj
2200hertz
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shubham
I am finding it hard to draw the velocity time graph, please can anyone assist me to know how to draw it, please?
bona
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v/6
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hmmm
Fortune
calculate the average velocity in time interval 6sec to 12sec ad determine the instantaneous velocity
Lekiisi
meaning of the term si units
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Chali
what what causes electric current
Chali
Charges(electron)
Caleb
Systeme international unitq@1qa@aaq
Caleb
Correct one international system of units.
Caleb
electric dynamo
albert
Electric dynamo is the sources of electric magnetic forces which utilize electromagnetic induction.
albert
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125m dip
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what is hypothesis theory law
Tamba
144.57m/s
physics is the science of measurement
What is physics
what is physics
Obaro
Good question! Physics is the study of the nature world . Does this help?
Yonn
physics is the study of matter in relations to energy.
Enoch
physics is the science of measurements
Jide
physics is a science concern with nature and properties of matter and energy
Ugomma
what is a parallelogram law of motion?
Nancy
describe how you would find the area of an irregular shaped body?
Chali
physics is the study of natural phenomena at their most fundamental level
Yaseer
Definition for physics
It deal with matter and relation to energy
Soughie
physics is the Study of matter in relation to energy.
albert
physics is a natural science that study matter its behaviour and relation to energy.
mohammed
physic tells us more about quantities and measurement also
Kelly
life as we know it that can be measured and calculated
Jesus
what is a reference frame
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The amount of time it takes a radioactive isotope to decay into a stable isotope is different for each radioactive isotope, and is characterized by its “half-life”. An isotope's half-life is the amount of time it takes for half the number of atoms of that isotope to decay to another isotope.
Nardine
what is the difference between Mass and weight
Pjustin
mass is constant while weight varies. unit of mass is kg, unit of weight is newton
Faith
how can a coin float in water and what principle governs it
in my opinion that work of surface tension but restrictions on coin is that coin do not break surface energy of molecules but some days before scientists prove that's another types of force
Aman
which force hold floating coins together thats my confusion
Aman