Addition or Removal of a Substance

Using these concentrations in the reaction quotient expression, we can calculate the value of for the reaction at this temperature as follows  

If we were to apply stress to this system by adding more N2, increasing its concentration from 2.05 M to 3.51 M, the system would no longer be at equilibrium. To see that this is true, use the new concentration of nitrogen in the reaction quotient expression. The new calculated value of (0.173) is no longer equal to the value of (0.297). 

Conversely, if we were to remove N2 from the original equilibrium mixture, the lower concentration in the denominator of the reaction quotient would result in Qc being greater than K. In this case the reaction will shift to the left. That is, the reverse reaction will take place, thereby increasing the concentrations of N2 and H2 and decreasing the concentration of NH3 until Qc is 

In essence, a system at equilibrium will respond to addition of a species by consuming some of that species, and it will respond to the removal of a species by producing more of that species. It is important to remember that addition or removal of a species from an equilibrium mixture does not change the value of the equilibrium constant K Rather, it changes temporarily the value of the reaction quotient, Q. Furthermore, in order to cau.se a shift in the equilibrium, the species added or removed must be one that appears in the reaction quotient expression. In the case of a heteroge- 

Sample Problem 15.11 shows the effects of stress on a system at equilibrium. 

Hydrogen sulfide (H2S) is a contaminant commonly found in natural gas. It is removed by reaction with oxygen to produce elemental sulfur. 

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Addition or Removal of a Substance Changes in Volume and Pressure Changes in Temperature Catalysis... 

The stresses that can be applied to a stem at equiliixium include the addition or removal of a substance, changes in the volume of the reaction vessel, and changes in the temperature. 

The removal of oxygen or the addition of hydrogen to a compound the opposite of oxidation. On the basis of the electronic theory of valency the meaning of the term has been extended to include all reactions in which there occurs an increase in the ratio of the electropositive to the electronegative atoms or groups of a substance. 

A recent (typically within a few months or less) initial exposure to the medication, a recent change in the dose of the medication, or a recent addition or removal of another psychoactive substance to the regimen... 

A polymer is defined by the International Union of Pure and Applied Chemistry (lUPAC) as a substance made of large molecules that is characterized by the multiple repetition of one or more species of atoms or group of atoms (called monomers or constitutional units) linked to each other covalently in amounts sufficient to provide a set of properties that do not vary markedly with the addition or removal of one or a few of the constitutional units. lUPAC and many other authorities... 

The derivation of the phase rule in this section uses the concept of components. The number of components, C, is the minimum number of substances or mixtures of fixed composition from which we could in principle prepare each individual phase of an equilibrium state of the system, using methods that may be hypothetical. These methods include the addition or removal of one or more of the substances or fixed-composition mixtures, and the conversion of some of the substances into others by means of a reaction that is at equilibrium in the actual system. 

Oxidation loss of electrons by a species during a chemical or electrochemical reaction addition of oxygen or removal of hydrogen from a substance. 

Chemical treatment is what the name implies-the addition of a foreign substance to effect the removal of unwanted substances. This includes such operations as neutralization, coagulation, ion exchange, and electrodialysis. These, along with the advanced physical systems, have been referred to at times as tertiary treatment or advanced treatment processes. 

Although crystals can be grown from the liquid phase—either a solution or a melt—and also from the vapour phase, a degree of supersaturation, which depends on the characteristics of the system, is essential in all cases for crystal formation or growth to take place. Some solutes are readily deposited from a cooled solution whereas others crystallise only after removal of solvent. The addition of a substance to a system in order to alter equilibrium conditions is often used in precipitation processes where supersaturation is sometimes achieved by chemical reaction between two or more substances and one of the reaction products is precipitated. 

In the case of a substance like Tris, or the food additive AF-2, the combination of an extremely widespread human exposure to the chemical and a positive result in a number of short-term tests should have been sufficient evidence to stop its use, considering that alternatives were available. Yet Tris and AF-2 were not removed from the market until the results from animal cancer tests indicated that they were carcinogens. It is becoming apparent that a positive result in many of these short-term test systems is meaningful, and that the systems may not only be a complement to animal cancer testing but may also provide much additional toxicological information as well. We... 

When iodine is dissolved in hydriodic acid or a soln. of a metallic iodide, there is much evidence of chemical combination, with the formation of a periodide. A. Baudrimont objected to the polyiodide hypothesis of the increased solubility of iodine in soln. of potassium iodide, because he found that an extraction with carbon disulphide removed the iodine from the soln. but S. M. Jorgensen showed that this solvent failed to remove the iodine from an alcoholic soln. of potassium iodide and iodine in the proportion KI I2, and an alcoholic soln. of potassium iodide decolorized a soln. of iodine in carbon disulphide. The hypothesis seemed more probable when, in 1877, G. S. Johnson isolated cubic crystals of a substance with the empirical formula KI3 by the slow evaporation of an aqueous-alcoholic soln. of iodine and potassium iodide over sulphuric acid. There is also evidence of the formation of analogous compounds with the other halides. The perhalides or poly halides—usually polyiodides—are products of the additive combination of the metal halides, or the halides of other radicles with the halogen, so. that the positive acidic radicle consists of several halogen atoms. The polyiodides have been investigated more than the other polyhalides. The additive products have often a definite physical form, and definite physical properties. J. J. Berzelius appears to have made the first polyiodide—which he called ammonium bin-iodide A. Geuther called these compounds poly-iodides and S. M. Jorgensen, super-iodides. They have been classified 1 as... 

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