In the example above, the double arrow shows that the reaction is an equilibrium reaction. This means that the forward reaction and the backward reaction can happen, usually due to a small enthalpy change in each reaction. Hence, the amount of product chemicals to reactant chemicals remains a fixed value, and such a ratio is called the equilibrium constant (K).
The equilibrium constant is a ratio of the concentration of the products raised to the appropriate powers to the concentration of the reactants raised to the appropriate powers. In the above example, the equilibrium constant is as follows:
formula_2
For some reactions, the equilibrium constant is very large, in which case nearly all of the reactant chemical is turned into products, such as when paper is burned. For other reactions, it is very small, which results in very little products being formed. If the equilibrium constant is close to 1, a mixture of both products and reactants is expected at equilibrium.
When chemists talk about equilibrium constants, they call reactions with large K values favorable and reactions with small K values unfavorable. It is important to note, however, these terms are not judgements about the value or usefulness of a particular chemical reaction. In fact, some very important reactions are actually "unfavorable"; one such example is the synthesis of ammonia from nitrogen and hydrogen gas (Haber process), which has a rather small equilibrium constant.
Understanding how chemical equilibriums work is important as it helps in understanding how a reaction happens. It allows chemists to calculate how much products will be formed from a reaction.
The concept of Le Chatelier's principle is important in predicting how an equilibrium will change when different factors are changed in a system. For example, using the Le Chatelier's principle, we are able to predict how the position of equilibrium will change when the concentration of a certain reactant/product has changed, as the system will try to counteract the change by favoring either the forward or the backward reaction
An exception to this rule is when an outside energy source forces the reaction to occur in the opposite direction, such as when a battery is recharged. Knowing the equilibrium constant of a reaction also helps you to understand the flow of energy that occurs during the reaction (thermodynamics).
Packet (computing)
In Information technology, a packet is collection of data that can be used by computers which need to communicate with each other, usually as part of a network. Some computers and networks do not use packets to communicate. But most currently do, including nearly all computers on the Internet. Packets allow many computers on a network to communicate more quickly and easily.
A packet consists of two kinds of data: packet information and packet "data" (or "payload"). If you think of a packet like a letter in the mail, the "control information" is like the outside of the envelope. There's an address that says where to send the letter, and a stamp that says how to send it (fast or slow). Similarly, the computer uses the "control information" in the packet to decide where, and how, to send the data. People aren't usually interested in the control information.
The "user data" is like the inside of the envelope. It is the actual information the computer is trying to send. This might be any kind of digital data, such as words, pictures, music, or computer programs. It's generally for people or computers to use, but not for the packet system to use.
Different communication protocols put the control information and user information in different places, or make it look different. But they still do the same thing.
Sometimes the computers make mistakes while transmitting data, or have trouble "hearing" each other. So many packets use a checksum or cyclic redundancy check to make sure they have the right information. This is usually one component of the control information. This helps to make sure the packets themselves have the right information. But then computers also need to get the right packets.
Designing computer networks can be difficult. Even though today's computers are very advanced, sometimes information doesn't arrive where it's supposed to. Sometimes computers try to fix this and end up sending it twice. And sometimes the information doesn't arrive in the right order. The Transmission Control Protocol, or TCP, was invented to fix these problems. But since it is complex, some computers use the User Datagram Protocol, or UDP, instead.
Errors and residuals in statistics
Statistical errors and residuals occur because measurement is never exact.
It is not possible to do an exact measurement, but it is possible to say how accurate a measurement is. One can measure the same thing again and again, and collect all the data together. This allows us to do statistics on the data. What is meant by errors and residuals is the difference between the observed or measured value and the real value, which is unknown.
If there is only one random variable, the difference between statistical errors and residuals is the difference between the mean of the population against the mean of the (observed) sample. In that case the residual is the difference between what the probability distribution says, and what was actually measured.
Suppose there is an experiment to measure the height of 21-year-old men from a certain area. The mean of the distribution is 1.75 m. If one man chosen at random is 1.80 m tall, the "(statistical) error" is 0.05 m (5 cm); if he is 1.70 tall, the error is −5 cm.
A residual (or fitting error), on the other hand, is an observable "estimate" of the unobservable statistical error. The simplest case involves a random sample of "n" men whose heights are measured. The "sample" mean is used as an estimate of the "population" mean. Then we have:
The sum of the residuals within a random sample must be zero. The residuals are therefore "not independent". The sum of the statistical errors within a random sample need not be zero; the statistical errors are independent random variables if the individuals are chosen from the population independently.
In sum:
Quartet
Generally speaking, a quartet is a group of four. In music, a quartet is a group of four people playing or singing four different parts to make a piece of music, such as a string quartet or a barbershop quartet.
Bank and Monument stations
Bank and Monument are interlinked stations, officially one station known operationally as the "Bank-Monument complex". However, separate names are used on station entrances, platforms and the tube map. The complex spans the length of King William Street in the City of London. Together they form the eighth busiest station on the network, being served by five London Underground lines and the Docklands Light Railway (DLR).
The two parts of the combined station take their names from the nearby Bank of England and the Monument to the Great Fire of London. The complex is in Travelcard Zone 1.
London Buses routes 8, 11, 21, 23, 25, 26, 40, 43, 76, 133, 141, 242 and 388 and night bus routes N8, N11, N21, N26, N76, N133, N550 and N551 serve the station.
Packet
Packet may refer to:
Barbican tube station
Barbican is a London Underground station serving the Barbican Centre in the City of London, England. It is on the Circle, Hammersmith & City and Metropolitan lines. It is between Farringdon and Moorgate. It is in Travelcard Zone 1. First Capital Connect trains used to stop at this station on their way to Moorgate station, but this stopped in March 2009. The outbound service calling here was abandoned many years before.
Barking station
Barking station is a railway station served by National Rail, London Underground and London Overground services. It is in Barking in the London Borough of Barking and Dagenham in East London. The station is in Zone 4 and is managed by c2c.
Barkingside tube station