Friday, March 26, 2010

More on Heat and Energy: Where is all the Hydrogen?

More on Heat and Energy: Where is all the Hydrogen?

In an earlier blog we address the fact that Hydrogen is not a truly clean alternative fuel. This is because hydrogen is not an available resource on this planet. It has to be manufactured which is a dirty process in itself. So the question is where is all the Hydrogen?

This is a relevant question considering Hydrogen is the most abundant visible element in the universe. It makes up the majority of the mass of the sun and most stars. Jupiter is 89% hydrogen, Saturn is 96% hydrogen…so what’s with earth?

Well to answer this question we need to take a brief look at the Zeroth Law of Thermodynamics.

Interestingly the zeroth law of thermodynamic is one of the most important laws discovered in science. Unfortunately it was not fully understood until after the first three laws where numbered and detailed, and dubbing it the 4th law seemed inappropriate. So in the 1920s Ralph Fowler a British physicist coined the term zeroth law to mark its significance. Although it’s erudite aspects took fertile and deep minds to resolve, its application is very simple in everyday experience.

When two things touch each other they tend to reach the same temperature. The more surface area in contact the greater the transfer of energy. Place a hot cup of coffee on a cold desk and it will get cold quick, place it with a small edge on the desk and the other on edge on a raised surface such as a post-it stack, and the surface of the bottom of the cup will be mostly in contact with cold air rather then the cold desk. Since air is not near the conductor of energy as average desk the coffee stay warmer longer. A simple thermometer works on the same principle. When a thermometer is in the air it tends to reach the same temperature as the air. This is true because the molecules in the air impart their kinetic energy too the molecules in the thermometer if the air is warmer. In the event the air is colder the molecules in the thermometer are more energetic then the molecules in the air and as the energetic molecules on the thermometer surface strike air molecules they lose energy to the air, much like a q-ball will stop or slow when it strikes a stationary ball on a pool table. This happens millions or billions of times and eventually the thermometer will either lose or give the kinetic energy of the motion of its molecules to the air if it was initially warmer then the air, or if the thermometer is initially colder it will acquire energy from the air. Either way, the air and thermometer will come to the same relative energy or temperature. Only when the relative energies or temperature of the two objects are the same does the flow of energies cease.

Now with that in mind, one more small detail is necessary to clarify. Just because two objects have the same temperature does not mean necessarily that the molecules in the objects are moving at the same speed. Since the temperature is the kinetic energy of the molecules this would make one thing clear, the smaller the molecule the faster it would have to move to have energy. Since energy is a product of the velocity and the mass, a molecule that is larger would move slower then a small molecule and yet have the same energy. This is much like a pool ball would have to be traveling at a considerably higher speed then a bowling ball to scatter the pins at the end of a bowling lane with the same vigor. In a similar fashion if one imagined a baseball moving at 90mph one can accept that a professional catcher could manage to catch it, but if one visualized a bowling ball traveling at 90mph striking a catcher we can reason the results would be dire. This is because the energy of the item is a product of speed and mass. So since this is true, in materials made up larger molecules their molecules average velocity would be less then materials at the same temperature made up of smaller molecules.

Ok, so once one can absorb the information above one can see why there is no or little hydrogen in earth’s atmosphere. If hydrogen was released into the atmosphere, because of the zeroth law of thermodynamics, we could reasonably conclude that it would have to reach the same temperature, and same energy as the air around it. That said, its velocity would have to be substantial enough to allow it to have the same kinetic energy as the surrounding air. Now with that in mind consider that hydrogen is the lightest of all atoms…it’s miserably lacking in mass, in fact its 1/16 the weight of oxygen. So in order to come to the same energy it has to move incredibly fast, so fast it actually has a velocity significant enough to escape the pull of earth’s gravity. Over time due to the average velocity that allows hydrogen atoms to exceed earths escape velocity ( we will go over escape velocity in later blogs) of approximately 25,000 mph frequently enough that eventually the majority of hydrogen has escaped our atmosphere. So because of zeroth law, kinetic energy, and high velocities hydrogen is scarce.

Few things to ponder now that we have clarified these points…what makes a helium balloon or hot air balloon rise? Most think it’s because helium or hot air is “lighter” or more “buoyant”…but the real reason is in the details above and revolve around energy, and velocity.

What makes your voice sound funny when you breathe helium? Some believe it’s because it affects your vocal cords, or that the pitch changes. When in reality helium has little or no effect on your vocal cords, and in fact the pitch of ones voice does not change. Rather, it’s the timber of your voice that changes, and the details of why are again found in the facts above.

1 comment:

  1. To add some clarity to the helium balloon note at the end here is some interesting info:

    Hot air balloon...its more buoyant because its hot or because its lighter? Its because its lighter so the equivalent volume of hot air displaces less then the cool air..i.e. same volume less mass. Why is this true? The atoms have increased energy/velocity/kinetic energy, thus they push upon each other with greater vigor creating more volume ... and if you contain them then that area that has the air with increased temperature/energy has less mass...this is all because of the increased energy/velocity of the atoms.

    To take that further. if you cooled helium to the point that the kinetic energy of the molecules was sufficiently low would not float...again you could say its because its density is greater then air at that point, but the density is a byproduct of the average energy/velocity of the molecules/atoms.

    Helium rises because the average velocity is greater then the air. If you heat the heavy atom gold to the point that its vaporized at 2,856C its less dense per volume, and at some point if the individual atoms in a vaporized gold where hot enough/energetic enough/high enough velocity and contained in a balloon (assuming you could get a balloon to resist the heat and assuming you could keep the gold that hot, since it would tend to want to come back to the energy of its surroundings per zeroth law) the gold filled balloon would rise ostensibly because it was less dense then the air, but fundamentally because the energy of the atoms caused them to collide against each other and the container they where in with such great vigor they would take up greater volume