![]() Continuous reactions occur over a range of conditions, so the products and reactants coexist stably over a range of conditions (but the compositions of the phases changes systematically as conditions change). Such reactions are more common than discontinuous reactions because compositional variation, of either fluid or solid phases, is typical for geological materials. Continuous reactions involve phases that may vary in composition.Discontinuous reactions are always net-transfer reactions. In a discontinuous reaction, products and reactants can only co-exist stably precisely at the equilibrium reaction conditions (on the reaction line in P-T space). (See the kyanite=sillimanite reaction on the phase diagram shown below.) On either side of the curve, a different set of phases is stable. For these, a curve (or line) can be drawn on a pressure-temperature (P-T) diagram. ![]() Discontinuous reactions are those that occur at a particular temperature (for a particular pressure). ![]() An example is:įe (in garnet) + Mg (in biotite) = Mg (in garnet) + Fe (in biotite)Ĭategorization based on reaction progress Exchange reactions involve chemical components being exchanged between phases, so compositions change, but modes remain the same (no phases disappear and no new phases are produced).Net-transfer reactions may be terminal reactions or tie-line flip reactions (discussed below). Net-transfer reactions involve chemical components being "transferred" from one phase or set of phases to others (new phases are produced as old ones disappear).Reactions among solid and fluid phases can be categorized in several different ways, based on what the reaction does, how the reaction progresses, or based on the nature of phases involved. w l is the mass fraction of the whole sample in the liquid phase.A 5 page summary (Acrobat (PDF) 158kB Aug1 07) of this information is available, which can be used as a class handout. The same equations can be used to find the mass fraction of alloy in each of the phases, i.e. The tie line drawn is from the solid alpha to the liquid and by dropping a vertical line down at these points the mass fraction of each phase is directly read off the graph, that is the mass fraction in the x axis element. There is now more than one two-phase region. Then the liquid concentration will start increasing.Įutectic phase diagrams Tie line in the Alpha plus Liquid two phase region If you're having difficulty realising why this is so, try visualising the composition when w o approaches w l. And then the denominator is the overall length of the arm so the difference between the solid and liquid compositions. That is if you want the mass fraction of solid then take the difference between the liquid composition and the original composition. The numerator of each equation is the original composition that we are interested in is +/- the opposite lever arm. Where w B is the mass fraction of element B for the given composition (represented as w o in this diagram). In an alloy or a mixture with two phases, α and β, which themselves contain two elements, A and B, the lever rule states that the mass fraction of the α phase is It can be used to determine the fraction of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus line. ![]() In chemistry, the lever rule is a formula used to determine the mole fraction ( x i) or the mass fraction ( w i) of each phase of a binary equilibrium phase diagram. Formula for determining the mole or mass fraction of phases in a binary phase diagram
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