UNDERSTANDING THERMODYNAMICSBASIC CHEMISTRY

Calorie is the unit to messure energy in the SI. Could you ever imagine how much energy is in a donut?

Let’s make an exercise to know it

The number of calories in a food is one way to measure the energy you get from that food. You'll get 226 calories, 12.7 grams of fat and 24.6 grams of carbohydrates, including 8.8 grams of sugar, if you consume a 3 1/4-inch plain cake doughnut. Add chocolate coating for frosting, and this goes up to 303 calories, 16.9 grams of fat and 34.4 grams of carbohydrates, including 17.9 grams of sugar for a 3 1/2-inch doughnut. A 3 3/4-inch glazed chocolate cake doughnut will set you back 250 calories, 11.9 grams of fat and 34.4 grams of carbohydrates, including 19.2 grams of sugar.

http://healthyeating.sfgate.com/energy-donuts-10719.html

How much energy is in a donut?

Yeast donuts

Should you favor the lighter and fluffier yeast doughnuts, you'll still be consuming a lot of calories, fat and sugar. A 3 3/4-inch glazed yeast doughnut has 269 calories, 14.5 grams of fat and 30.7 grams of carbohydrates, including 14.6 grams of sugar. Make that a 3 1/2- by 2 1/2-inch cream-filled yeast doughnut, and you'll be consuming 307 calories, 20.8 grams of fat and 25.5 grams of carbohydrates, including 12.4 grams of sugar. Swap out the cream filling for jelly, and the same-size doughnut contains 289 calories, 15.9 grams of fat and 33.2 grams of carbohydrates, including 17.9 grams of sugar.

http://healthyeating.sfgate.com/energy-donuts-10719.html

THERMODYNAMICS temperatura scales The Celsius, Kelvin, and Fahrenheit temperature scales are shown in

relation to the phase change temperatures of water. The Kelvin scale is called absolute temperature and the Kelvin is the SI unit for temperature.

Rankine Scale

The Rankine Scale For some engineering purposes, the Rankine scale is used. The degree

size is the same as the Fahrenheit degree, and the zero of the scale is absolute zero. Often just R for "Rankines" is used rather than °R for expressing Rankine temperatures. The zero of the Rankine scale is -459.67°F (absolute zero) and the freezing point of water is 491.67R = 32°F.

Zeroth Law of Thermodynamics

The "zeroth law" states that if two systems are at the same time in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

Heat transfer

The transfer of heat is normally from a high temperature object to a lower temperature object. Heat transfer changes the internal energy of both systems involved according to the First Law of Thermodynamics.

Calculating Home Heating Energy

Heat transfer from your home can occur by conduction, convection and radiation. It is typically modeled in terms of conduction, although infiltration through walls and around windows can contribute a significant additional loss if they are not well sealed. Radiation loss can be minimized by using foil-backed insulation as a radiation barrier.

The U.S. heating and air conditioning industry uses almost entirely the old British and U.S. common units for their calculations. For compatibility with the commonly encountered quantities, this example will be expressed in those units.

Material Thermal conductivity(cal/sec)/(cm2 C/cm)

Thermal conductivity(W/m K)*

Diamond ... 1000

Silver 1.01 406.0

Copper 0.99 385.0

Gold ... 314

Brass ... 109.0

Aluminum 0.50 205.0

Iron 0.163 79.5

Steel ... 50.2

Lead 0.083 34.7

Mercury ... 8.3

Ice 0.005 1.6

Glass,ordinary 0.0025 0.8

Concrete 0.002 0.8

Water at 20° C 0.0014 0.6

Asbestos 0.0004 0.08

Snow (dry) 0.00026 ...

Fiberglass 0.00015 0.04

Brick,insulating ... 0.15

Brick, red ... 0.6

Cork board 0.00011 0.04

Wool felt 0.0001 0.04

Rock wool ... 0.04

Polystyrene (styrofoam) ... 0.033

Polyurethane ... 0.02

Wood 0.0001 0.12-0.04

Air at 0° C 0.000057 0.024

Helium (20°C) ... 0.138

Hydrogen(20°C) ... 0.172

Nitrogen(20°C) ... 0.0234

Oxygen(20°C) ... 0.0238

Silica aerogel ... 0.003

Heat Conduction

Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole. If one end of a metal rod is at a higher temperature, then energy will be transferred down the rod toward the colder end because the higher speed particles will collide with the slower ones with a net transfer of energy to the slower ones. For heat transfer between two plane surfaces, such as heat loss through the wall of a house, the rate of conduction heat transfer is:

Calculation

First Law of Thermodynamics

The first law of thermodynamics is the application of the conservation of energy principle to heat and thermodynamic processes:

Second Law of Thermodynamics

The second law of thermodynamics is a general principle which places constraints upon the direction of heat transfer and the attainable efficiencies of heat engines. In so doing, it goes beyond the limitations imposed by the first law of thermodynamics. It's implications may be visualized in terms of the waterfall analogy.

Second Law: Heat Engines

Second Law of Thermodynamics: It is impossible to extract an amount of heat QH from a hot reservoir and use it all to do work W . Some amount of heat QC must be exhausted to a cold reservoir. This precludes a perfect heat engine.

This is sometimes called the "first form" of the second law, and is referred to as the Kelvin-Planck statement of the second law.

Second Law: Refrigerator

Second Law of Thermodynamics: It is not possible for heat to flow from a colder body to a warmer body without any work having been done to accomplish this flow. Energy will not flow spontaneously from a low temperature object to a higher temperature object. This precludes a perfect refrigerator. The statements about refrigerators apply to air conditioners and heat pumps, which embody the same principles.

This is the "second form" or Clausius statement of the second law.

Second Law: Entropy

Second Law of Thermodynamics: In any cyclic process the entropy will either increase or remain the same.

Since entropy gives information about the evolution of an isolated system with time, it is said to give us the direction of "time's arrow" . If snapshots of a system at two different times shows one state which is more disordered, then it could be implied that this state came later in time. For an isolated system, the natural course of events takes the system to a more disordered (higher entropy) state.

Carnot Cycle The most efficient heat engine cycle is the Carnot cycle, consisting of two

isothermal processes and two adiabatic processes. The Carnot cycle can be thought of as the most efficient heat engine cycle allowed by physical laws. When the second law of thermodynamics states that not all the supplied heat in a heat engine can be used to do work, the Carnot efficiency sets the limiting value on the fraction of the heat which can be so used.

In order to approach the Carnot efficiency, the processes involved in the heat engine cycle must be reversible and involve no change in entropy. This means that the Carnot cycle is an idealization, since no real engine processes are reversible and all real physical processes involve some increase in entropy.