An Explanation of the Ideal Gas Law

An Explanation of the Ideal Gas Law The Ideal Gas Law is one of the Equations of State. Although the law describes the behavior of an ideal gas, the equation is applicable to real gases under many conditions, so it is a useful equation to learn to use. The Ideal Gas Law may be expressed as: PV NkT where:P absolute pressure in atmospheresV volume (usually in liters)n number of particles of gask Boltzmanns constant (1.38Â ·10−23 JÂ ·K−1)T temperature in Kelvin The Ideal Gas Law may be expressed in SI units where pressure is in pascals, volume is in cubic meters, N becomes n and is expressed as moles, and k is replaced by R, the Gas Constant (8.314 JÂ ·K−1Â ·mol−1): PV nRT Ideal Gases Versus Real Gases The Ideal Gas Law applies to ideal gases. An ideal gas contains molecules of a negligible size that have an average molar kinetic energy that depends only on temperature. Intermolecular forces and molecular size are not considered by the Ideal Gas Law. The Ideal Gas Law applies best to monoatomic gases at low pressure and high temperature. Lower pressure is best because then the average distance between molecules is much greater than the molecular size. Increasing the temperature helps because of the kinetic energy of the molecules increases, making the effect of intermolecular attraction less significant. Derivation of the Ideal Gas Law There are a couple of different ways to derive the Ideal as Law. A simple way to understand the law is to view it as a combination of Avogadros Law and the Combined Gas Law. The Combined Gas Law may be expressed as: PV / T C where C is a constant that is directly proportional to the quantity of the gas or number of moles of gas, n. This is Avogadros Law: C nR where R is the universal gas constant or proportionality factor. Combining the laws: PV / T nRMultiplying both sides by T yields:PV nRT Ideal Gas Law Problems Ideal vs Non-Ideal Gas ProblemsIdeal Gas Law - Constant VolumeIdeal Gas Law - Partial PressureIdeal Gas Law - Calculating MolesIdeal Gas Law - Solving for PressureIdeal Gas Law - Solving for Temperature Ideal Gas Equation for Thermodynamic Processes Process(Constant) KnownRatio P2 V2 T2 Isobaric(P) V2/V1T2/T1 P2=P1P2=P1 V2=V1(V2/V1)V2=V1(T2/T1) T2=T1(V2/V1)T2=T1(T2/T1) Isochoric(V) P2/P1T2/T1 P2=P1(P2/P1)P2=P1(T2/T1) V2=V1V2=V1 T2=T1(P2/P1)T2=T1(T2/T1) Isothermal(T) P2/P1V2/V1 P2=P1(P2/P1)P2=P1/(V2/V1) V2=V1/(P2/P1)V2=V1(V2/V1) T2=T1T2=T1 isoentropicreversibleadiabatic(entropy) P2/P1V2/V1T2/T1 P2=P1(P2/P1)P2=P1(V2/V1)−Î ³P2=P1(T2/T1)ÃŽ ³/(ÃŽ ³ − 1) V2=V1(P2/P1)(−1/ÃŽ ³)V2=V1(V2/V1)V2=V1(T2/T1)1/(1 − ÃŽ ³) T2=T1(P2/P1)(1 − 1/ÃŽ ³)T2=T1(V2/V1)(1 − ÃŽ ³)T2=T1(T2/T1) polytropic(PVn) P2/P1V2/V1T2/T1 P2=P1(P2/P1)P2=P1(V2/V1)−nP2=P1(T2/T1)n/(n − 1) V2=V1(P2/P1)(-1/n)V2=V1(V2/V1)V2=V1(T2/T1)1/(1 − n) T2=T1(P2/P1)(1 - 1/n)T2=T1(V2/V1)(1−n)T2=T1(T2/T1)

The U.S. Militarys Space Operations

The U.S. Militarys Space Operations People love a good military conspiracy theory, including the one that the Air Force has its very own space shuttle. It all sounds very James Bond, but the truth is that the military actually never had a secret space shuttle.  Instead, it used NASAs space shuttle fleet until 2011. Then it built and flew its own mini-shuttle drone and continues to test it on long missions. However, while there may be great interest within the military for a space force, theres just not one out there. There is a space command at the U.S. Air Force, mainly interested in working through issues of armed forces using space resources. However, there arent phalanxes of soldiers up there, just a lot of interest in what military use of space might eventually become. The U.S. Military in Space The  theories about the military use of space stem largely from the fact that the U.S. Department of Defense flew secret missions on the shuttles when NASA was still using them to get to space. Interestingly, when NASAs fleet was being developed, there were plans to make  additional copies exclusively for military purposes. That affected the specifications of the shuttle design, such as the length of its glide path, so that the vehicle could accommodate military and top-secret missions. There was also a shuttle launch facility built in California, at Vandenberg Air Force Base. This complex, called SLC-6 (Slick Six), was supposed to be used to put shuttle missions into polar orbits. However, after the Challenger exploded  in 1986, the complex was put into caretaker status and was never used for a shuttle launch. The facilities were mothballed until the military decided to retool the base for satellite launches. It was used to support Athena launches until 2006 when Delta IV rockets began to lift off from the site.   Use of the Shuttle Fleet for Military Operations Ultimately, the military decided that having dedicated shuttlecraft for the military was unnecessary. Given the amount of technical support, staff, and facilities required to run such a program, it made more sense to use other resources to launch payloads into space. In addition, more sophisticated spy satellites were developed to accomplish reconnaissance missions. Without its own fleet of shuttles, the military relied on NASAs vehicles to meet its needs for access to space. In fact, the space shuttle Discovery was planned to be available to the military as its exclusive shuttle, with civilian use as it was available. It was even going to be launched from the militarys Vandenbergs SLC-6 launch complex. Ultimately the plan was scrapped following the Challenger disaster. In recent years, the space shuttle fleet has been retired and new spacecraft are being designed to take humans to space.   For years, the military used whatever shuttle was available at the time of need, and military payloads were launched from the usual launchpad at Kennedy Space Center. The last shuttle flight strictly for military use was carried out in 1992 (STS-53). The subsequent military cargo was taken up by shuttles as a secondary part of their missions. Today,  with the increasingly reliable use of rockets via NASA and SpaceX (for example), the military has much more cost-effective access to space.   Meet the X-37B Mini-shuttle Drone While the military hasnt had a need for a conventional manned orbiting vehicle, some situations could call for a shuttle-type craft.  However, these craft will be quite different from the current stable of orbiters- perhaps not in look, but definitely in function. The X-37 shuttle  is a good example of where the military is going with a shuttle-type spacecraft. It  was originally designed as a potential replacement for the current shuttle fleet. It had its first successful flight in 2010, launched from atop a rocket. The  craft carries no crew, its missions are secret, and it is entirely robotic. This mini-shuttle has flown several long-term missions, most likely performing reconnaissance flights and specific types of experiments.   Clearly, the military is interested in the ability to place objects into orbit as well as have reusable spy craft; the expansion of projects like the X-37 thus seems entirely possible and very likely will continue into the foreseeable future. The U.S. Air Force space command, with bases and units around the globe, is the front line for space-based missions, and also focuses on cyberspace capabilities for the country, as needed.   Could There Ever Be a Space Force? Occasionally politicians float  the idea of a space force. What that force would be or how it would be trained are still very large unknowns. There are few facilities to get soldiers ready for the rigors of fighting in space. As well, theres been no talk by veterans of such training, and expenditures for such places would eventually show up in budgets. However, if there was to be a space force, massive changes to military structures would be needed. As mentioned, training would have to ramp up on a scale so far unknown to any military on the planet. Thats not to say one couldnt be created in the future, but there isnt one now.   Edited and updated by Carolyn Collins Petersen.