Specific Heat Capacity - 03/31/07 05:14 PM
Please correct me if I'm wrong (as if I really had to say that;-)
The concept of Greenhouse Gas stems from an observation by Arrhenius a while back that the temperature of a glass cyclinder containing a gas rose as he shined a light on it.
We all agree that the Sun's radiant energy, of all wavelengths, strikes the surface of our planet, is absobed, warming the surface. That energy flows from the warmer surface to the cooler atmosphere, mostly in infra-red wave lengths. Without an atmosphere, that energy would just vanish quickly into space.
Although EM radiation can be correlated to temperature (as in the "background temp of the universe") only matter can really have temperature: it's a measure of the average kinetic energy of the molecules in the sample, and by extension, of their average velocity.
Empirical studies show that each different substance absorbs IR energy to a characteristic extent. The amount of energy needed to raise the temp of a standard volume of a given gas by 1degC is defined as that gas' specific heat capacity.
For the inert gases, all the heat absorbed by the single atom can only be used to increase the velocity of the atom (translational energy). The inert gases are all found to have sp heat cap very close to a single value, about 1.0 relative units.
For the di-atomic molecules, some energy absorbed is diverted to rotating the molecule about its center of mass, so it takes more energy input (also allowing for the higher mass) to get the temp up by the 1deg than for the inert gases. The sp heat cap of the di-atomics is about 1.3 relative units.
For tri-atomics, and additional degree of freedom occurrs with the geometry: not only can the molecule use absorbed energy to increase its translational and its rotational speeds, but now the angle between the three atoms can vary (vibrational energy), so it takes even more input to get the molecules up to speed for the 1 deg increase in temp. Sp heat cap for these is about 1.6 rel units.
I believe the GHG Theory suggests that having absorbed this energy, the gas molecules are free to re-radiate it off to another molecule. and the process is iterated, delaying the ultimate fate of each photon to be lost to space. But as each molecule re-radiates its absorbed photon, it slows back down, so when the neighboring molecule absorbs the second hand photon, the net change in the energy of the two molecules is zero. So, in the Grenhouse Phenomenon, the GHG doesn't "generate" energy, it just delays the loss of energy to space.
Secondly, note that sp heat capacity doesn't mean any given substance is "better" at absorbing energy, only that it takes more energy to get its temp up- ie- the "stronger" substances actually help to keep the temp lower for any given energy input.
This is where I believe GW theory has perverted the concept of sp heat cap. It claims CO2 is a more efficient absorber, whereas, it should only be stated that it helps keep temps down by absorbing energy not used to increase its translational velocity.
Now it may be a co-incidence, but if we use those relative sp heat cap figures above, the known concentrations of atmospheric gases, and an average world temp of 288degK, then it?s an easy algebra ?mixing problem? to calculate that a rise in CO2 from 300ppm to 600ppm results in an increase to about 288.5degK- consistent with the GHG Theory. If that?s how the experts are calculating it, then isn?t that wrong?
The concept of Greenhouse Gas stems from an observation by Arrhenius a while back that the temperature of a glass cyclinder containing a gas rose as he shined a light on it.
We all agree that the Sun's radiant energy, of all wavelengths, strikes the surface of our planet, is absobed, warming the surface. That energy flows from the warmer surface to the cooler atmosphere, mostly in infra-red wave lengths. Without an atmosphere, that energy would just vanish quickly into space.
Although EM radiation can be correlated to temperature (as in the "background temp of the universe") only matter can really have temperature: it's a measure of the average kinetic energy of the molecules in the sample, and by extension, of their average velocity.
Empirical studies show that each different substance absorbs IR energy to a characteristic extent. The amount of energy needed to raise the temp of a standard volume of a given gas by 1degC is defined as that gas' specific heat capacity.
For the inert gases, all the heat absorbed by the single atom can only be used to increase the velocity of the atom (translational energy). The inert gases are all found to have sp heat cap very close to a single value, about 1.0 relative units.
For the di-atomic molecules, some energy absorbed is diverted to rotating the molecule about its center of mass, so it takes more energy input (also allowing for the higher mass) to get the temp up by the 1deg than for the inert gases. The sp heat cap of the di-atomics is about 1.3 relative units.
For tri-atomics, and additional degree of freedom occurrs with the geometry: not only can the molecule use absorbed energy to increase its translational and its rotational speeds, but now the angle between the three atoms can vary (vibrational energy), so it takes even more input to get the molecules up to speed for the 1 deg increase in temp. Sp heat cap for these is about 1.6 rel units.
I believe the GHG Theory suggests that having absorbed this energy, the gas molecules are free to re-radiate it off to another molecule. and the process is iterated, delaying the ultimate fate of each photon to be lost to space. But as each molecule re-radiates its absorbed photon, it slows back down, so when the neighboring molecule absorbs the second hand photon, the net change in the energy of the two molecules is zero. So, in the Grenhouse Phenomenon, the GHG doesn't "generate" energy, it just delays the loss of energy to space.
Secondly, note that sp heat capacity doesn't mean any given substance is "better" at absorbing energy, only that it takes more energy to get its temp up- ie- the "stronger" substances actually help to keep the temp lower for any given energy input.
This is where I believe GW theory has perverted the concept of sp heat cap. It claims CO2 is a more efficient absorber, whereas, it should only be stated that it helps keep temps down by absorbing energy not used to increase its translational velocity.
Now it may be a co-incidence, but if we use those relative sp heat cap figures above, the known concentrations of atmospheric gases, and an average world temp of 288degK, then it?s an easy algebra ?mixing problem? to calculate that a rise in CO2 from 300ppm to 600ppm results in an increase to about 288.5degK- consistent with the GHG Theory. If that?s how the experts are calculating it, then isn?t that wrong?