Effect of Reactant Concentrations

Reaction of Iron(III) Chloride with Ammonium Thiocyanate. 

Prepare for this experiment a 0.01-0.02 M solution of iron(III) -chloride and a 0.02-0.03 M solution of ammonium thiocyanate. Pour into a beaker 20 ml each of the iron(III) chloride and ammonium ithiocyanate solutions. How can the red colour of the solution be 

Pour the solution obtained into four test tubes. Keep the first one as a reference. Add to the second tube two or three drops of a concentrated iron(III)j chloride solution, to the third one two or three drops of a concentrated ammonium thiocyanate solution, and to the fourth one a small amount of dry ammonium chloride. Stir the contents of the test tubes and observe the change in the intensity of the colour of the solutions. 

Explain the occurring phenomena on the basis of the law of meiss action. Will equilibrium be shifted if the obtained solutions are diluted The concentration of what substance changes from one experiment to another, and how many times What conclusion should be made from the results obtained  

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The effect of reactant concentrations on reaction rate was studied using unpromoted skeletal copper catalysts initially leached at 278 K and then... 

The Effect of Reactant Concentration. Several experiments were conducted to quantify the effect of reactant concentration on the aldehyde reduction rate. The initial CO pressure was varied... 

The effect of reactant concentration can be divided into two separate influences. The simplest is obvious Lower overall concentrations result in a slower rate. This does not necessarily mean a thinner fihn, however—sometimes the opposite. The reason for this is clear if we return to our introductory discussion on the CD process—rapid precipitation. It is clear that if the reaction is too fast, it will terminate with most of the product precipitating homogeneously in solution rather than depositing on the substrate (which requires time to occur). This results in a very thin film, if any fihn at all. Similarly, for the less extreme case of a CD reaction that terminates, not within a second, but still in a short time, the final fihn thickness will be small. At the other extreme, if the reaction is extremely slow, a thick fihn can be built up, but it may take a very long time for this to occur (weeks, even months). It is therefore evident that there is an optimum rate for the reaction, which can be controlled by a combination of reactant concentrations, temperature, and pH. 

Titration curves in Figure 7-6 illustrate the effect of reactant concentration. The equivalence point is the steepest point of the curve. It is the point of maximum slope (a negative slope in this case) and is therefore an inflection point (at which the second derivative is 0) ... 

Steven W. Wright, "Tick Tock, a Vitamin C Clock/ J. Chem. Educ., Vol. 79, 2002,40A-40B. This article presents an activity that uses supermarket chemicals to perform a clock reaction in which the endpoint is signaled by an abrupt change in appearance from colorless to blue-black. This activity can be used to explore reaction kinetics and the effect of reactant concentrations on the apparent rate of reaction. 

Scherer MM, Tratnyek PG. Dechlorination of carbon tetrachloride by iron metal effect of reactant concentrations. 209th National Meeting, Anaheim, CA, American Chemical Society 1995 35(l) 805-806. 

Ethane thiol reacts more readily than the methyl compound, but the main features of the reaction (e.g. the effect of reactant concentration) are similar. The products include some acid (assumed to be peracetic or acetic) as well as sulphur dioxide and acetaldehyde the large sulphur deficit is again ascribed to disulphide formation. In oxygen-rich mixtures all the sulphur is converted to sulphur dioxide. 

Effect of Reactant Concentration on Reaction Rate (70). Effect... 

General support for this type of reaction scheme is afforded by investigations on the effect of reactant concentrations. An excess of phosphorus pentachloride gives a high yield of the linear end-stopped bodies the proportion of these petrol-insoluble compounds can be reduced almost to zero by extracting the phosphorus pentachloride slowly into a refluxing suspension of ammonium chloride in tetrachloroethane (/). 

Fig. 2. Reaction of 0NCO with HjO in dioxane at 23°C in the presence of triethylene diamine (0,0014 M). Effect of reactant concentration. [HjO] = J [0NCO].

In earlier chapters, we considered the effects of reactant concentrations and completeness of the reaction on titration curves. Here, we describe the effects of these variables on oxidation/reduction titration curves. 

For experiments in which the temperature was varied, the temperature was increased stepwise with constant feed composition and total flow. For determining the effect of contact time, measurements were made at a series of total flows between 50 - 300 cm min" with either 100 or 250 mg of catalyst. The flow was varied in a random way rather than sequentially, to avoid any bias in the data. Similarly, for determining the effect of reactant concentration, the concentration of one reactant was varied in a non-sequential manner, while the concentration of the other reactants was kept constant. The catalyst was treated with 20% 02/He for 15 min at 480°C between experiments using different hydrocarbons to remove any hydrocarbon residues from the catalyst. 

One way to study the effect of reactant concentration on reaction rate is to determine how the initial rate depends on the starting concentrations. It is preferable to measure the initial rates because as the reaction proceeds, the concentrations of the reactants decrease and it may become difficult to measure the changes accurately. Also, there may be a reverse reaction of the type... 

Fig. 10.8. Effect of reactant concentrations in the aqueous cycloaddition of methyl vinyl ketone to isoprene (7 = 303.2 K). Reaction time = 20 h at 0.1 MPa and 3 h at 200 Mpa. [isoprene] [ketone] = 1.1 1, total volume is 2.5 mL.

One of the earliest addition reactions studied is that which takes place between trimethyl phosphite and 2-nitrobut-2-ene, and which illustrates the effect of reactant concentrations on the course of the reaction. When reactant concentrations are high, the phosphorane 60 is isolable, whereas at low reactant concentrations, the product is the oxime 61, formed from 60 through a process initiated by the transfer of a proton from... 

Scherer, M. M. Tratnyek, P. G. (1995) Dechlorination of carbon tetrachloride by iron metal Effect of reactant concentration. 209th American Chemical Society National Meeting. Division of Environmental Chemistry Preprints of Papers, Anaheim, California, pp. 805-806. 

Equation (3.40) is quite general and describes the effect of reactant concentration on rate, not only at the start of the reaction in the complete absence of P (in the forward direction) or A (in the reverse direction), but also at any time during the approach to equilibrium (Alberty, 1959 Qeland, 1963, 1977). 

The effect of Cl on CO, methane, and ethane oxidation reactions on Pt/AljOj catalysts is shown in Figure 17.3. The plots in the left panels correspond to the conversion at different temperatures, and those in the right, to the Arrhenius plots. The turnover frequency (TOF) values used to obtain the Arrhenius plots were obtained at low conversion (<15%) to minimize the effect of reactant concentration. 

Effect of Reactant Concentrations on the Apparent Equilibrium Constant of Monoses ... 

An overhead projector demonstration of the effect of reactant concentration on equilibrium. Lee R. Summerlin and james L. Ealy, jr., "Equilibrium and Le Chatelier s Principle," Chemical Demonstrations, A Sourcebook for Teachers, Vol. 1 (American Chemical Society, Washington, DC, 1988) 77-78. 

The determination of the time dependence of the rate of a chain reaction and the study of the effects of reactants concentrations and of incident light intensity are used techniques for the elucidation of the ki of chain reactions. The best way to establisl three parameters is to change them separately... 

A more complex case of so-called cross-catalytic reactions may involve two reactants A and B and two products Z and P. The intermediates are X and Y and the catalytic loop is caused by multiplication of the intermediates X, see the scheme above. Figure 63 above may well illustrate the input effect of reactant concentration within the given reaction mechanism (at the threshold concentration of A the steady sub-critical region changes from the sterile to the fertile course of action capable of oscillations in supercritical region. Although first assumed hypothetically, it enabled to visualize the autocatalytic nature of many processes and gave to them the necessary practical dimension when applied to various reality situations ... 

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