<< Chapter < Page Chapter >> Page >

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 C . The warmer the air is, the faster this heat exchange occurs and the faster the snow melts.

Got questions? Get instant answers now!

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 = mL, size 12{Q= ital "mL"} {}

    where L size 12{L} {} is the latent heat coefficient.

Conceptual questions

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

Got questions? Get instant answers now!

How does the latent heat of fusion of water help slow the decrease of air temperatures, perhaps preventing temperatures from falling significantly below 0ºC size 12{"0°C"} {} , in the vicinity of large bodies of water?

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

If you place 0ºC size 12{"0°C"} {} ice into 0ºC size 12{"0°C"} {} water in an insulated container, what will happen? Will some ice melt, will more water freeze, or will neither take place?

Got questions? Get instant answers now!

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?

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

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] .

Got questions? Get instant answers now!

Problems&Exercises

How much heat transfer (in kilocalories) is required to thaw a 0.450-kg package of frozen vegetables originally at C size 12{0°C} {} if their heat of fusion is the same as that of water?

35.9 kcal

Got questions? Get instant answers now!
Practice Key Terms 3

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics for ap® courses' conversation and receive update notifications?

Ask