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Educational Services. Featured Products. Resources Discontinued Products. Application Notes. The additional greenhouse gases are contributing to global warming and to associated climatic changes.
The global average concentration of water vapour quickly rises in response to an increase in global temperature, due to the increased water-holding capacity of a warmer atmosphere. Because water vapour is a greenhouse gas, the original warming is amplified.
This amplification is known as a positive feedback. Half of the CO 2 released to the atmosphere is absorbed by natural CO 2 sinks, on the land and in the ocean, helping to mitigate emissions from human activities. How the kinetic-molecular picture finally came to be universally accepted is a fascinating piece of scientific history and is discussed briefly below in the section Kinetic theory of gases.https://freesubwoopho.tk
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Any theory of gas behaviour based on this kinetic model must also be a statistical one because of the enormous numbers of particles involved. The kinetic theory of gases is now a classical part of statistical physics and is indeed a sort of miniature display case for many of the fundamental concepts and methods of science.
Such important modern concepts as distribution functions, cross sections, microscopic reversibility, and time-reversal invariance have their historical roots in kinetic theory, as does the entire atomistic view of matter. When considering various physical phenomena, it is helpful for one to have some idea of the numerical magnitudes involved.
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In particular, there are several characteristics whose values should be known, at least within an order of magnitude a factor of 10 , in order for one to obtain a clear idea of the nature of gaseous molecules. These features include the size, average speed, and intermolecular separation at ordinary temperatures and pressures. In addition, other important considerations are how many collisions a typical molecule makes in one second under these conditions and how far such a typical molecule travels before colliding with another molecule.
With this knowledge, one could calculate at least some of the gas values. It is interesting to see how the answers could be estimated from simple observations and then to compare the results to the accepted values that are based on more precise measurements and theories.
One of the easiest properties to work out is the average distance between molecules compared to their diameter; water will be used here for this purpose. The liquid occupies a volume of 1. Thus, the average volume occupied by one molecule in the gas is larger than the corresponding volume occupied in the liquid by a factor of 1. Since volume varies as the cube of distance, the ratio of the mean separation distance in the gas to that in the liquid is roughly equal to the cube root of 1,, or about If the molecules in the liquid are considered to be touching each other, the ratio of the intermolecular separation to the molecular diameter in ordinary gases is on the order of 10 under ordinary conditions.
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It should be noted that the actual separation and diameter cannot be determined in this way; only their ratio can be calculated. It is also relatively simple to estimate the average speed of gas molecules.
Looking for a Gas
Consider a sound wave in a gas, which is just the propagation of a small pressure disturbance. If pressure is attributed to molecular impacts on a test surface, then surely a pressure disturbance cannot travel faster than the molecules themselves. In other words, the average molecular speed in a gas should be somewhat greater than the speed of sound in the gas.
This value depends on the particular gas and the temperature, but it will be sufficient for the kind of estimates sought here. The average molecular speed, along with an observed rate of the diffusion of gases, can be used to estimate the length and tortuosity of the path traveled by a typical molecule. If a bottle of ammonia is opened in a closed room, at least a few minutes pass before the ammonia can be detected at a distance of just one metre.