12.2 Changes of State and Thermodynamics
The three most common states of matter
Figure 12 Temperature vs Heat: adding thermal energy to water
Diagram showing names for the various changes of state
From solid to gas, without melting: Sublimation
An unusual example of freezing
When sea ice melts, it leaves behind brine that is so salty it sinks. A brinicle forms when sea water freezes around the descending salt. As the underwater icicle moves toward the sea floor, it kills nearly everything in its path by encasing it in ice. A film crew for the BBC was the first to capture this phenomenon on camera.
Read more at http://www.businessinsider.sg/amazing-natural-phenomena-2014-3/3/#4DHVGgWo8QuhSYSs.99
The triple point
Heat of fusion / Heat of vaporization, p.331
heat of fusion = amount of energy needed to melt 1 kg of a substance
heat of vaporization = amount of energy needed to vaporize 1 kg of a substance
The heat of fusion process can be seen in countless applications …in the manufacturing industry… coin making, glassblowing, forging metal objects, and transforming blow molded plastics into household products.
They all require heat of fusion to become a final product. The change in your wallet, the glass vase on your fireplace mantel, and the plastic soda bottle from the vending machine all went through a heat of fusion manufacturing process.
In coin making, solid zinc and copper (metals in American pennies) are placed into a casting furnace and heated by the heat of fusion process until they reach the liquid phase.
Once in the liquid phase, the molten zinc and copper are poured into a mold, and cast into long bars.
In the casting process, the molten metal transforms from the liquid phase to the solid phase, becoming a solid bar. The long bars are flattened by heavy machinery and stamped into thousands of coins. Without the heat of fusion process, a monetary system would not exist in the United States.
Energy and changes of states
p.332. We’re not covering this section.
Laws of thermodynamics
How does a heat engine transform thermal energy into mechanical energy (to do work) and waste heat?
Internal combustion engines
We cover internal combustion engines here.
Refrigerator energy diagram
space inside the frig = cold reservoir
space outside the frig (rest of the kitchen) = hot reservoir.
An electrically powered compressor supplies the work.
W = electrical energy taken from the wall outlet
Qc = heat sucked out of the cold reservoir
Qh = waste heat dumped into the room
2nd law of thermodynamics
The second law of thermodynamics is sometimes stated as “disorder increases over time”.
Details of the 2nd law are covered in AP Physics. View the laws of thermodynamics here., and the 2nd law of thermodynamics here.
Entropy is an advanced topic covered in AP Physics or AP Chemistry. Entropy is covered here.
Chapter 13, Section 1, page 354.
Why ice floats
Quick video of ice molecules melting into liquid water
Examine animations and examples of: Solids, Liquids, Gases, Solutions, Boiling, Evaporation, Sublimation, Deposition.
We’ll also ask: is everything a solid, liquid or gas? If not, what else is there?
Practical uses: Changes of States
The following section is excerpted from: Science Clarified: Science of Everyday Things
A liquid crystal is a substance that, over a specific range of temperature, displays properties both of a liquid and a solid. Below this temperature range, it is unquestionably a solid, and above this range it is just as certainly a liquid. In between, however, liquid crystals exhibit a strange solid-liquid behavior: like a liquid, their particles flow, but like a solid, their molecules maintain specific crystalline arrangements.
The cholesteric class of liquid crystals is so named because the spiral patterns of light through the crystal are similar to those which appear in cholesterols. Depending on the physical properties of a cholesteric liquid crystal, only certain colors may be reflected. The response of liquid crystals to light makes them useful in liquid crystal displays (LCDs) found on laptop computer screens, camcorder views, and in other applications.
LIQUEFACTION OF GASES.
One interesting and useful application of phase change is the liquefaction of gases, or the change of gas into liquid by the reduction in its molecular energy levels. Liquefied natural gas (LNG) and liquefied petroleum gas (LPG), the latter a mixture of by-products obtained from petroleum and natural gas, are among the examples of liquefied gas in daily use. In both cases, the volume of the liquefied gas is far less than it would be if the gas were in a vaporized state, thus enabling ease and economy of transport.
Liquefied gases are used as heating fuel for motor homes, boats, and homes or cabins in remote areas. Other applications of liquefied gases include liquefied oxygen and hydrogen in rocket engines; liquefied oxygen and petroleum used in welding; and a combination of liquefied oxygen and nitrogen used in aqualung devices. The properties of liquefied gases figure heavily in the science of producing and studying low-temperature environments. In addition, liquefied helium is used in studying the behavior of matter at temperatures close to absolute zero.
Coal gasification is the conversion of coal to gas… Though widely used as a fuel in power plants, coal, when burned by ordinary means, generates enormous air pollution. Coal gasification, on the other hand, makes it possible to burn “clean” coal. Gasification involves a number of chemical reactions, some exothermic or heat-releasing, and some endothermic or heat-absorbing…
The finished product of coal gasification is a mixture containing carbon monoxide, methane, hydrogen, and other substances, and this—rather than ordinary coal—is burned as a fuel. The composition of the gases varies according to the process used. Products range from coal synthesis gas and medium-Btu gas to substitute natural gas.
8.MS-PS1-4. Develop a model that describes and predicts changes in particle motion, relative spatial arrangement, temperature, and state of a pure substance when thermal energy is added or removed. Emphasis is on qualitative molecular-level models of solids, liquids, and gases to show that adding or removing thermal energy increases or decreases kinetic energy of the particles until a change of state occurs
HS-PS3-2. Develop and use a model to illustrate that energy at the macroscopic scale can be accounted for as either motions of particles and objects or energy stored in fields.
Clarification Statements: Examples of phenomena at the macroscopic scale could include evaporation and condensation, the conversion of kinetic energy to thermal energy,
HS-PS3-4a. Provide evidence that when two objects of different temperature are in thermal contact within a closed system, the transfer of thermal energy from higher temperature objects to lower-temperature objects results in thermal equilibrium, or a more uniform energy distribution among the objects and that temperature changes
necessary to achieve thermal equilibrium depend on the specific heat values of the two substances. Energy changes should be described both quantitatively in a single phase (Q =m·c·∆T) and conceptually either in a single phase or during a phase change.
HS-PS3-3. Design and evaluate a device that works within given constraints to convert one form of energy into another form of energy.
• Emphasis is on both qualitative and quantitative evaluations of devices.
• Examples of devices could include Rube Goldberg devices, wind turbines, solar
cells, solar ovens, and generators.
• Examples of constraints could include use of renewable energy forms and
PS1.A Structure of matter: That matter is composed of atoms and molecules can be used to explain the properties of substances, diversity of materials, how mixtures will interact, states of matter, phase changes, and conservation of matter. States of matter can be modeled in terms of spatial arrangement, movement, and strength of interactions between particles. Characteristic physical properties unique to each substance can be used to identify the substance.