Two key points are worth emphasizing. Take water H 2 O as an example. However, if heat is added, some of the solid H 2 O will melt and turn into liquid H 2 O.
If heat is removed, the opposite happens: some of the liquid H 2 O turns into solid H 2 O. Water is a good substance to use as an example because many people are already familiar with it. Other substances have melting points and boiling points as well. Again, consider H 2 O as an example. Only after all of the solid has melted into liquid does the addition of heat change the temperature of the substance.
For each phase change of a substance, there is a characteristic quantity of heat needed to perform the phase change per gram or per mole of material. Remember that a phase change depends on the direction of the heat transfer. If heat transfers in, solids become liquids, and liquids become solids at the melting and boiling points, respectively.
If heat transfers out, liquids solidify, and gases condense into liquids. At these points, there are no changes in temperature as reflected in the above equations. How much heat is necessary to melt The heat of fusion of H 2 O is Note the units on these quantities; when you use these values in problem solving, make sure that the other variables in your calculation are expressed in units consistent with the units in the specific heats or the heats of fusion and vaporization.
This phase change is called sublimation. Each substance has a characteristic heat of sublimation associated with this process. We encounter sublimation in several ways. You may already be familiar with dry ice, which is simply solid carbon dioxide CO 2. Solid carbon dioxide is called dry ice because it does not pass through the liquid phase. When considering phase changes, the closer molecules are to one another, the stronger the intermolecular forces.
For any given substance, intermolecular forces will be greatest in the solid state and weakest in the gas state. The boiling points of ethyl ether and ethanol are Which substance has stronger intermolecular forces?
As a liquid boils, it is undergoing the liquid to gas phase change. In order to do this, the intermolecular forces present in the liquid state must be overcome.
Stronger intermolecular forces will require more energy to be overcome. A higher boiling point means more energy is required to overcome the intermolecular forces present in the liquid state. A solid will merely vibrate, although your eyes cannot detect this.
A liquid will allow atoms to roll around each other but not bounce out of their container. A gas is of such a high temperature that the molecules are literally bouncing off the container and taking up as much space as they are allowed.
Remember--the higher the energy level or temperature, the faster and farther apart the atoms move. When converting the temperature of 0 o C to the Kelvin scale, you would say 0 o C is equal to Kelvins. P re K Education. Canvas Logins Find an Institution. Resources and services for Utah Higher Education faculty and students such as Canvas and collegEmedia.
Content and resources for career literacy and preparation. Career Ed News. Our goal is to educate, engage, and enrich the lives of Utah residents through broadcast programs and services. On-Demand Support , opt. Tech Services Sort It Out! It is Cold!
0コメント