Simply a suggestion: keep in mind the laws of the NATURE

I actually have seen many discussions, which I, of course, regard very high of. However, I realized that in some cases, some augument might be judged by "if it observes the law of the first and second thermodynamics law".

The first states that: You can convert energy, but you cannot creat or destroy energy.

The second states: the entrope of an isolated system will never decrease. Or equivalently, it is impossible to convert heat completely into work, or heat does not flow from lower temperature to higher temperature spontaneously, or "you cannot get internal energy from a system without affecting the enviornment." etc...

Sometimes we also apply the third: you cannot reach zero degree kelvin.



Some times, people try to creat energy from zero, maybe God can do it. Human being cannot.

Sometimes people are trying to get some "internal energy" but don't want to pay attention to the effects of the environment. Yes, there are all kinds of energy around us. But for many type, you simply cannot make use, or you need to input much more energy to make use of a certain type of energy with much less output, the rest dissipated into the environment.

Some people sometimes claim they can use "zero point energy" of a crystal to do work, etc.

The above are abvious violation of the law of thermodynamics. You might argue, why must we observe these laws? Hard to answer, but we might have to be scientific and those laws are the foundation of sciences, proven by many many's work.

I am not saying we must be slaves of a certain doctrine, however, it is not advisable "not to observe these laws".. This is different from "not encouraging novel ideas", or "he was bought by an organization to criticize the new ideas"...

Science is science.

[edit on 6-3-2008 by fuelcell]

[edit on 6-3-2008 by fuelcell]

In daily life free energy might mean "energy for free money". In physics, free energy has a different meaniing.

For a system in thermodynamics, we have a state function enthalpy, H, which is related to another state function G, (Gibbs) free energy, and entropy, S, as shown by Equation 1.

H = G + TS (1)

where T is the absolute temperature (in K). For a process, the change of these state functions are shown as in Equation 2.

Δ G = Δ H – Δ (TS) (2)

If this process is in constant temperature and constant pressure, then we re-write Equation 2 into Equation 3:

Δ G = Δ H – T Δ S (3)

where Δ G is the difference of free energy, or change in free energy. Δ H equals to the heat effect in this process, and Δ S is the change in entropy. Here, this Δ G is the most possible energy you can exploit from a system in a process.

An exothermic chemical reaction can convert the heat energy into electricity. For example, the oxidation of hydrogen as in fuel cells, can give out heat. At a constant pressure (1 atm, 298 K), 1 mole of hydrogen can generate heat of 286 kJ (Δ H = -286 kJ) upon combustion, this is called the chemical energy of hydrogen. However, when hydrogen is used in fuel cell, you cannot exploit all this 286 kJ and change it into electric energy because it need to deal with the entropy change (Δ S = -163.2 J/K = -0.1632 kJ/K ), you can only obtain a portion of it, as shown in Equation 4.

Δ G = Δ H – T Δ S = -286- 298*(-0.163) = - 237 kJ

This shows that only 237 kJ out of 286 kJ of the chemical energy, or, 83%, could be possibly converted into electric energy. This is the theoretical energy efficient of a hydrogen fuel cell. The rest of the energy is inevitably dissipated into the environment. There is no way we convert the energy in a 100% efficiency. That portion of energy that can be converted into electricity is therefore called (change in) free energy.