How can the woodward hoffman rules determine whether cyclization proceeds by light or heat?
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The basic idea is that in any chemical reaction, the HOMO of one molecule interacts with the LUMO of another, and the result is that a chemical bond is formed. \n\nThere are two criteria for this to happen. First, the energy difference between the HOMO and LUMO must be small. Second, there must be enough overlap between the HOMO and LUMO for the bond to form.\n\nIt also turns out that in order to get good overlap, you must have the same symmetry of the two orbitals. The amount of overlap is calculated as the integral of the product of the two wavefunctions. If the orbitals have opposite symmetry, this integral cancels out to zero and you have no overlap. However, if the orbitals have the same symmetry, it's possible they can form a bond.\n\nThe Woodward-Hoffman rules are just an easy way to predict which reactions will have favorable symmetry so that orbital overlap is possible and the reaction can potentially form a bond. \n\nThe issue of heat vs light is an issue of which orbital is the HOMO. If you excite a molecule with uv light, you can promote and electron to the next higher orbital. This means that the HOMO is now different from the ground state, and will have a different symmetry than the ground state. As a result, it is going to overlap well with different LUMOs and allow for different reactivity.\n\nNeedless to say, the Woodward Hoffman rules simplify a lot of quantum physics into some very short and sweet rules with amazing predictive ability. Roald Hoffman definitely deserved the Nobel Prize in 1981 for this work, and there is little doubt that R. B. Woodward would have received his second Nobel had he been alive in 1981.
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Specific heat does not apply to reactions, only actual chemicals.  You are probably thinking of the heat of reaction, or enthalpy.  The change in enthalpy of a reaction (written as delta H, delta as the Greek letter that looks like a little triangle) flips its sign when the reaction is run in the reverse direction.  So a positive delta H value becomes negative when the reaction is run in reverse direction, and a negative delta H value becomes positive.
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It depends on the wavelength of the light and its energy.
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You need to look up the entropy for all compounds, multiply by the entropy by the stochiometric coefficients (e.g. 4 for NH3, 3 for O2). Then subtract the left side from the right side.\n\nVery simple actually, once you find the data.
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understanding the reaction meachanism \neffect of catalysts etc....\ndetermining the amounts needed
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Synthesis - a compound forms from simpler reactants
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D is the correct answer, Light enables photosynthesis so a and c are wrong, and no reaction can increase exponentially as in B
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detlaH=H(products) - H(Reactants)\n\n200KJ/mol
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Ahh, a pharamacology question!  If one plots a Michaelis-Menten graph of the data, in order to determine any variables of the reaction, you have to "eyeball" it and make your best estimation- Transformation into a Lineweaver-Burk plot yields a straight-line graph- From this graph you can determine exactly the reaction variables.\nThe y-interecept is 1/Vmax, the x-intercept is 1/Km, and the slope is Km/Vmax. So, with a little Junior High algebra, you can determine Km and  Vmax for the reaction exactly, without subjective determination.\n\nSo: \n1) you can determine Km and Vmax and\n2) L-B plots allow exact determination of these variables, while M-M plots do not-you have to make a best estimation on them
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the minimum amount of energy required to start a reaction
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Correct.\nD. when delta G is positive the reaction is non-spontaneous
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At temperatures above 220 K the rxn would be spontaneous. To determine spontaneity, first determine the delta G value by using the formula deltaG=deltaH-Tdelta S. Now find out what temperature value would make the delta G negative which would indicate a spontaneous rxn, and in this case it is spontaneous above 220 K.
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3C2H2----->C6H6 this is called polymerisation.the reaction takes place when acetylene is passed through a red hot copper tube
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a compound contaning carbon
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RT , in gaschromotography depends mainly on the boiling points of the compounds in the mixture , the molecular weight ,the low boiling point, low molecular wieght has the lowest RT , the polartiy of the compound affected the RT depending on the column used.
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in simple terms; it does not matter how many steps it took to get to the end, what matters are the first and last points.\n\nfor example: when travelling in a circle, your distance is the circumfrence of the circle and the DISPLACEMENT is ZERO because you started and ended in the same place.\nDisplacement is a state function. \n\nsecond example: Hess's Law, a set of chemical reactions are added together to make one overall equation. A set of reactants forms products, and those products are reactants for another reaction that also occurs, these are elementary steps, or intermediates. The end product, where the products are not reacting further in another reaction. The OVERALL chemical equation does not take into account the elementary steps, it only shows the initial reactants and the final products. Thus, it is a state fuction.
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&#92;\n..&#92;\n..-----&#92;\n........&#92;\n.........&#92;\n(ignore the periods)\nx axis: time\nY axis: temperature\nThe step is there because the nature of cooling objects. As the naphthalene is cooled, its temp first decreases normally. However, when it begins to solidify, the heat being removed is used up as naphthalene molecules are subjected to intermolecular forces and begin to become a solid. Therefore, the horzontal part is where the substance becomes a solid. Finally, when the naphthalene is fully a solid, the temperature decreases again. An easy way to picture this concept is with boiling water. As some water molecules change to the gaseous state, the temperature of the water does not rise above its boiling point. This is equivilent to the horzontal part of the naphthalene cooling curve. As the substance changes states, energy is being generated/used up, and the temperature does not change for a time. When the conversiion is fully made, the temperature continus on its original course.