Law of Definite Proportions Definition

Law of Definite Proportions Definition The law of definite proportions, together with the law of multiple proportions, forms the basis for the  study of stoichiometry  in chemistry. The law of definite proportions is also known as Prousts law or the law of constant composition. Law of Definite Proportions Definition The law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. The mass ratio of elements is fixed no matter where the elements came from, how the compound is prepared or any other factor. Essentially, the law is based on the fact that an atom of a particular element is the same as any other atom of that element. So, an atom of oxygen is the same, whether it comes from silica or oxygen in air. The Law of Constant Composition is an equivalent law, which states each sample of a compound has the same composition of elements by mass. Law of Definition Proportions Example The law of definite proportions says water will always contain 1/9 hydrogen and 8/9 oxygen by mass. The sodium and chlorine in table salt combine according to the rule in NaCl. The atomic weight of sodium is about 23 and that of chlorine is about 35, so from the law one may conclude dissociating 58 grams of NaCl would produce about 23 g of sodium and 35 g of chlorine. History of the Law of Definite Proportions Although the law of definite proportions may seem obvious to a modern chemist, the manner in which elements combine was not obvious in the early days of chemistry through the end of the 18th century. French chemist Joseph Proust (1754–1826) is credited with the discovery, but English chemist and theologian Joseph Priestly (1783–1804) and French chemist Antoine Lavoisier (1771–1794) were the first to publish the law as a scientific proposal in 1794, based on the study of combustion. They noted metals always combine with two proportions of oxygen. As we know today, oxygen in the air is a gas consisting of two atoms, O2. The law was hotly disputed when it was proposed. French chemist Claude Louis Berthollet (1748–1822) was an opponent, arguing elements could combine in any proportion to form compounds. It wasnt until English chemist John Dalton (1766–1844)s atomic theory explained the nature of atoms that the law of definite proportions became accepted. Exceptions to the Law of Definite Proportions Although the law of definite proportions is useful in chemistry, there are exceptions to the rule. Some compounds are non-stoichiometric in nature, meaning their elemental composition varies from one sample to another. For example, wustite is a type of iron oxide with an elemental composition varying between 0.83 and 0.95 iron atoms for each oxygen atom (23%–25% oxygen by mass). The ideal formula for iron oxide is FeO, but the crystal structure is such that there are variations. The formula for wustite is written Fe0.95O. Also, the isotopic composition of an element sample varies according to its source. This means the mass of a pure stoichiometric compound will be slightly different depending on its origin. Polymers also vary in element composition by mass, although they are not considered true chemical compounds in the strictest chemical sense.

Leonard Susskind - Theoretical Physicist

Leonard Susskind - Theoretical Physicist In 1962, Leonard Susskind earned a B.A. in physics from City College of New York after transitioning from his plan to get a degree in engineering. He earned his Ph.D. in 1965 from Cornell University. Dr. Susskind worked at Yeshiva University as an Associate Professor from 1966 to 1979, with a year at University of Tel Aviv from 1971 to 1972, before becoming a Professor of Physics at Stanford University in 1979, where he remains to this today. He was awarded the Felix Bloch Professorship of Physics since the year 2000. String Theory Insights Probably one of Dr. Susskinds most profound accomplishments is that hes credited as one of the three physicists who independently realized, back in the 1970s, that a certain mathematical formulation of particle physics interactions seemed to represent oscillating springs ... in other words, hes considered one of the fathers of string theory. He has done extensive work within string theory, including the development of a matrix-based model. Hes also responsible for one of the more recent discoveries in the exploration of theoretical physics, the holographic principle, which many, including Susskind himself, believe will provide great insights into how string theory applies to our universe. In addition, in 2003 Susskind coined the term string theory landscape to describe the set of all physically possible universes that could have come into being under our understanding of the laws of physics. (At present, this could contain as many as 10500 possible parallel universes.) Susskind is a strong proponent of applying reasoning based upon the anthropic principle as a valid means to evaluate which physical parameters its possible for our universe to have. Black Hole Information Problem One of the most troubling aspects of black holes is that when something falls into one, it is lost to the universe forever. In the terms that physicists use, information is lost ... and that isnt supposed to happen. When Stephen Hawking developed his theory that black holes actually radiated an energy known as Hawking radiation, he believed that this radiation would be insufficient to actually resolve the problem. The energy radiating out from the black hole under his theory would not contain enough information to fully describe all of the matter that fell into the black hole, in other words. Leonard Susskind disagreed with this analysis, believing quite strongly that the conservation of information was so important to the underlying foundations of quantum physics that it could not be violated by black holes. Ultimately, the work in black hole entropy and Susskinds own theoretical work in developing the holographic principle have helped to convince most physicists - including Hawking himself - that a black hole would, over the course of its lifetime, emit radiation that contained the full information about everything that ever fell into it. Thus most physicists now believe that no information is lost in black holes. Popularizing Theoretical Physics Over the last few years, Dr. Susskind has become more well-known among lay audiences as a popularizer of advanced theoretical physics topics. He has written the following popular books on theoretical physics: The Cosmic Landscape: String Theory and the Illusion of Intelligent Design (2005) - This book presents Susskinds view of how string theory predicts a vast string theory landscape and how the anthropic principle can be applied to evaluate the various physical properties of our universe against all of the assorted possibilities. This is described above in the string theory section.The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics (2008) - In this book, Susskind describes the black hole information problem (described above), framed as an intriguing narrative about a disagreement within the theoretical physics community ... one which has taken decades to resolve.The Theoretical Minimum: What You Need to Know to Start Doing Physics with George Hrabovsky (2013) - A math-based introduction to the fundamental concepts within classical mechanics, such as conservation of energy and symmetries in physical laws, which is intended to lay the groundwor k for what someone would need to know to proceed to the next level in physics. This is based on lectures that are available online, as described below. In addition to his books, Dr. Susskind has presented a series of lectures that are available online through both iTunes and YouTube ... and which provide the basis of The Theoretical Minimum. Here is a list of the lectures, in roughly the order that I would recommend viewing them, along with links to where you can view the videos for free: Classical Mechanics (YouTube) - A 10-lecture series focusing on the fundamentals of classical mechanicsThe Theoretical Minimum: Quantum Mechanics (YouTube) - A 10-lecture series that tries to understand what physicists know about quantum mechanicsSpecial Relativity (YouTube) - A 10-lecture series explaining Einsteins theory of special relativityGeneral Relativity (YouTube) - A 10-lecture series that lays out the modern theory of gravity: general relativityParticle Physics: Standard Model (YouTube) - A 9-lecture series focusing on the Standard Model of particle physicsCosmology (YouTube) - A 3-lecture series focusing on what we know and understand about the history and structure of our universeString Theory and M-Theory (YouTube) - A 10-lecture series focusing on the fundamentals of string theory and M-TheoryTopics in String Theory (YouTube) - A 9-lecture series focusing on the fundamentals of string theory and M-Theory As you may have noticed, some of the themes repeat between lecture series, such as the two different lecture sets on string theory, so you shouldnt need to watch them all if there are redundancies ... unless you really want to.