The Effect of Concentration

The more people there are in a crowded room, the greater is the likelihood that people will bump into each other. In the same way, if we increase the number, or concentration, of the reacting species, it should make sense that molecules will collide with each other more often. In the case of gases, since pressure increases with concentration, we can also say that gases react faster at higher pressures. In either case, collision theory tells us that an increase in the frequency of collisions results in products being formed at a faster rate. 

An example would be taking T ims for an upset stomach. Turns are made of CaCOj and react with acid to generate CO gas (see Chapter 9). If the concentration of stomach acid (HCl) is low, COj will be generated very slowly and you may not even notice it. If the concentration of stomach acid is high, however, CO will be generated rapidly, the result probably being a loud belch as excess CO escapes from your digestive system. 

Molecules travel faster at higher temperatures, so at higher temperatures we expect two results  

Any molecule that has kinetic energy equal to or in excess of the activation energy for the reaction, can potentially become products. 

But even then remember that molecules must come together with the proper orientation. 

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A = 4.05 X lO " cm/(s-kPa)(4.1 X 10 cm/(s-atm)) and = 1.3 x 10 cm/s (4)//= 1 mPa-s(=cP), NaCl diffusivity in water = 1.6 x 10 cm /s, and solution density = 1 g/cm . Figure 4 shows typical results of this type of simulation of salt water permeation through an RO membrane. Increasing the Reynolds number in Figure 4a decreases the effect of concentration polarization. The effect of feed flow rate on NaCl rejection is shown in Figure 4b. Because the intrinsic rejection, R = 1 — Cp / defined in terms of the wall concentration, theoretically R should be independent of the Reynolds... 

Siddiqi-Lucas suggested that component volume fractions might be used to correlate the effects of concentration dependence. They found an average absolute deviation of 4.5 percent for nonpolar-nonpolar mixtures, 16.5 percent for polar-nonpolar mixtures, and 10.8 percent for polar-polar mixtures. 

Law of Mass Action The effect of concentration on the rate is isolated as... 

The possibility of preconcentration of selenium (IV) by coprecipitation with iron (III) hydroxide and lanthanum (III) hydroxide with subsequent determination by flame atomic absorption spectroscopy has been investigated also. The effect of nature and concentration of collector and interfering ions on precision accuracy and reproducibility of analytical signal A has been studied. Application of FefOH) as copreconcentrant leads to small relative error (less than 5%). S, is 0.1-0.2 for 5-100 p.g Se in the sample. Concentration factor is 6. The effect of concentration of hydrochloric acid on precision and accuracy of AAS determination of Se has been studied. The best results were obtained with HCl (1 1). 

The effect of concentration of cationic (cetylpyridinium chloride, CPC), anionic (sodium dodecylsulfate, SDS) and nonionic (Twin-80) surfactants as well as effect of pH value on the characteristics of TLC separ ation has been investigated. The best separ ation of three components has been achieved with 210 M CPC and LIO M Twin-80 solutions, at pH 7 (phosphate buffer). Individual solution of SDS didn t provide effective separation of caffeine, theophylline, theobromine, the rate of separ ation was low. The separ ation factor and rate of separ ation was increase by adding of modifiers - alcohol 1- propanol (6 % vol.) or 1-butanol (0.1 % vol.) in SDS solution. The optimal concentration of SDS is 210 M. 

Through all these calculations of the effect of pH and metal ions on the ATP hydrolysis equilibrium, we have assumed standard conditions with respect to concentrations of all species except for protons. The levels of ATP, ADP, and other high-energy metabolites never even begin to approach the standard state of 1 M. In most cells, the concentrations of these species are more typically 1 to 5 mM or even less. Earlier, we described the effect of concentration on equilibrium constants and free energies in the form of Equation (3.12). For the present case, we can rewrite this as... 

Fructose is present outside a cell at 1 /iM concentration. An active transport system in the plasma membrane transports fructose into this cell, using the free energy of ATP hydrolysis to drive fructose uptake. Assume that one fructose is transported per ATP hydrolyzed, that ATP is hydrolyzed on the intracellular surface of the membrane, and that the concentrations of ATP, ADP, and Pi are 3 mM, 1 mM, and 0.5 mM, respectively. T = 298 K. What is the highest intracellular concentration of fructose that this transport system can generate Hint Kefer to Chapter 3 to recall the effects of concentration on free energy of ATP hydrolysis.)... 

It has been emphasised that the oxygen reduction reaction is diffusion controlled, and it might be thought that the nature of the metal surface is unimportant compared with the effect of concentration, velocity and temperature that all affect /Y and hence. However, in near-neutral solutions the surface of most metals will be coated (partially or completely) with either... 

The effects of concentration, velocity and temperature are complex and it will become evident that these factors can frequently outweigh the thermodynamic and kinetic considerations detailed in Section 1.4. Thus it has been demonstrated in Chapter 1 that an increase in hydrogen ion concentration will raise the redox potential of the aqueous solution with a consequent increase in rate. On the other hand, an increase in the rate of the cathodic process may cause a decrease in rate when the metal shows an active/passive transition. However, in complex environmental situations these considerations do not always apply, particularly when the metals are subjected to certain conditions of high velocity and temperature. 

Beer s Law. We have so far considered the light absorption and the light transmission for monochromatic light as a function of the thickness of the absorbing layer only. In quantitative analysis, however, we are mainly concerned with solutions. Beer studied the effect of concentration of the coloured constituent in solution upon the light transmission or absorption. He found the same relation between transmission and concentration as Lambert had discovered between transmission and thickness of the layer [equation (3)], i.e. the intensity of a beam of monochromatic light decreases exponentially as the concentration of the absorbing substance increases arithmetically. This may be written in the form ... 

For pure substances, n is usually held constant. We will usually be working with molar quantities so that n = 1. The number of moles n will become a variable when we work with solutions. Then, the number of moles will be used to express the effect of concentration (usually mole fraction, molality, or molarity) on the other thermodynamic properties. 

The Structures of Simple Molecules.—The foregoing considerations throw some light on the structure of very simple molecules in the normal and lower excited states, but they do not permit such a complete and accurate discussion of these questions as for more complicated molecules, because of the difficulty of taking into consideration the effect of several unshared and sometimes unpaired electrons. Often the bond energy is not great enough to destroy s-p quantization, and the interaction between a bond and unshared electrons is more important than between a bond and other shared electrons because of the absence of the effect of concentration of the eigenfunctions. 

The effect of temperature on adsorption was also stndied. At low temperatnre (i.e., near 0°C) adsorption proceeds very slowly, while at high temperatnre (40°C) the snrface coverage varies strongly from sample to sample, indicating side effects snch as partial desorption. Final valnes of always approached 30%, independent of the temperatnre. The effects of concentration and temperature on the surface coverage are clearly not compatible with a description of the adsorption behavior by Fangmnir s eqnation. 

The effect of concentration on the rate of a particular chemical reaction can be summarized in an algebraic expression known as a rate law. A rate law links the rate of a reaction with the concentrations of the reactants through a rate constant (jt ). In addition, as we show later in this chapter, the rate law may contain concentrations of chemical species that are not part of the balanced overall reaction. 

The effects of concentration or dilution of the active ingredient on the activity of a disinfectant are of paramount importance. Failure to be aware of these changes in activity is responsible for many misleading claims concerning the properties of a disinfectant. 

Thus, the ideas above do not suffice for an interpretation of all experimental results. These ideas include the assumption that the ions move in the membrane only under the effect of concentration and potential gradients (diffusion and migration), and that transport of one sort of ions is independent of the transport of other sorts of ions. This transport of ions under the effect of external forces has been named passive ionic transport. 

The effect of concentrated nitric acid on thiols is potentially dangerous. It forms a sulphonic acid ... 

Neglecting the effects of concentration changes on solvent density, the phase... 

Hydrogenation of lactose to lactitol on sponge itickel and mtheitium catalysts was studied experimentally in a laboratory-scale slurry reactor to reveal the true reaction paths. Parameter estimation was carried out with rival and the final results suggest that sorbitol and galactitol are primarily formed from lactitol. The conversion of the reactant (lactose), as well as the yields of the main (lactitol) and by-products were described very well by the kinetic model developed. The model includes the effects of concentrations, hydrogen pressure and temperature on reaction rates and product distribution. The model can be used for optinuzation of the process conditions to obtain highest possible yields of lactitol and suppressing the amounts of by-products. 

Explain why magnesium metal, rather than copper metal, might be used to study the effect of concentration of hydrochloric acid on rates of reactions. 

It is not usual to talk about the resistance of electrolytes, but rather about their conductance. The specific conductance (K) of an electrolyte is defined as the reciprocal of the resistance of a part of the electrolyte, 1 cm in length and 1 cm2 in cross-sectional area. It depends only on the ions present and, therefore it varies with their concentration. To take the effect of concentration into account, a function called the equivalent conductance, A, is defined. This is more commonly (and conveniently) used than the specific conductance to compare quantitatively the conductivities of electrolytes. The equivalent conductance A is the conductance of that volume of the electrolyte which contains one gram equivalent of the ions taking part in the electrolysis and which is held between parallel electrodes 1 cm apart (units ohm-1 cm4). If V cubic centimeters is the volume of the solution containing one gram equivalent, then the value of L will be 1 cm and the value of A will be V square centimeters, so that... 

We have examined the effects of concentration, temperature, solvent and added electrolyte on the kinetics of this structural interconversion. In all instances, the kinetics are well described by the rate law for a reversible first-order reaction [Equation 1] ... 

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