REACTION RATE IS INFLUENCED BY CONCENTRATION AND TEMPERATURE

What mass of water is produced when 16 grams of methane, CH4 (formula mass 16 atomic mass units), burn in the reaction 

Step 2. Use the coefficients of the balanced equation to find out bow many moles of H20 are produced from this many moles of CH4  

How many grams of ozone (03,48 amu) can be produced from 64 grams of oxygen (02,32 amu) in tbe reaction 

Step 3. Now that you know how many moles of H20 are produced, convert this value to grams of H20  

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The qualitative idea that reaction rate is influenced by the frequency and energy of reactant collisions leads to several quantitative questions How can we describe the dependence of rate on reactant concentration mathematically Do all changes in concentration affect the rate to the same extent Do all rates increase to the same extent with a given rise in temperature How do reactant molecules use the collision energy to form product molecules, and is there a way to determine this energy What do the reactants look like as they are turning into products We address these questions in the following sections. 

The study of reaction rates or kinetics of a particular denaturation process of a protein therapeutic can provide valuable information about the mechanism, i.e., the sequence of steps that occur in the transformation of the protein to chemically or conformationally denatured products. The kinetics tell something about the manner in which the rate is influenced by such factors as concentration, temperature, excipients, and the nature of the solvent as it pertains to properties of protein stability. The principal application of this information in the biopharmaceutical setting is to predict how long a given biologic will remain adequately stable. 

Stone et al. (S29) developed by a mathematical analysis the functional relationship between the rate of extraction of silica from pure quartz in sodium hydroxide solution and time, temperature, sodium hydroxide concentration, and particle size. With the use of response surface methodology, a comprehensive picture of this dissolution process was obtained from a few well-chosen experiments. The fractional extraction of silica can be expressed by a second-order equation. The effect of quartz particle size and temperature are predicted to be about equal and greater than the influence of sodium hydroxide concentration and reaction time. The reaction rate is controlled by the surface area of the quartz. An increase in sodium hydroxide concentration increases the activation energy for the reactions and is found to be independent of quartz size. 

Subsequently, we will learn by the example of homogeneous non-catalytic reactions (and so without any influence of mass transport) how the rate is influenced by the temperature and the concentration of the reactants (Section 4.3.1). We then inspect simple systems consisting of two parallel or two series reactions (Section 4.3.2), reversible reactions (Section 4.3.3), and how to consider a change in volume of a system (Section 4.3.4). 

The rate of a chemical reaction is influenced by pressure, temperature, concentration of reactants, kinetic factors such as agitation, and the presence of a catalyst. Since the viability of a plant depends not only on reaction efficiencies but also on the capital cost factor and the cost of maintenance, it may be more economic to alter a process variable in order that a less expensive material of construction can be used. The flexibility which the process designer has in this respect depends on how sensitive the reaction efficiency is to a change in the variable of concern to the materials engineer. 

So far, what has been examined is the effect of the concentrations of the reactants and the products on the reaction rate at a given temperature. That temperature also has a strong influence on reaction rates can be very effectively conveyed by considering the experimentally found data on the formation of water from a mixture of hydrogen and oxygen. At room temperature the reaction will not take place hence the reaction rate is zero. At 400 °C it is completed in 1920 h, at 500 °C in 2 h, and at 600 °C the reaction takes place with explosive rapidity. In order to obtain the complete rate equation, it is also necessary to know the role of temperature on the reaction rate. It will be recalled that a typical rate equation has the following form ... 

The catalyst activity depends not only on the chemical composition but also on the diffusion properties of the catalyst material and on the size and shape of the catalyst pellets because transport limitations through the gas boundary layer around the pellets and through the porous material reduce the overall reaction rate. The influence of gas film restrictions, which depends on the pellet size and gas velocity, is usually low in sulphuric acid converters. The effective diffusivity in the catalyst depends on the porosity, the pore size distribution, and the tortuosity of the pore system. It may be improved in the design of the carrier by e.g. increasing the porosity or the pore size, but usually such improvements will also lead to a reduction of mechanical strength. The effect of transport restrictions is normally expressed as an effectiveness factor q defined as the ratio between observed reaction rate for a catalyst pellet and the intrinsic reaction rate, i.e. the hypothetical reaction rate if bulk or surface conditions (temperature, pressure, concentrations) prevailed throughout the pellet [11], For particles with the same intrinsic reaction rate and the same pore system, the surface effectiveness factor only depends on an equivalent particle diameter given by... 

Intrinsic kinetic data can only be measured provided that the overall reaction rate is not limited by mass transport. Only then reahstic parameters can be calculated concerning the influence of catalyst and substrate concentrations (reaction order) as well as the temperature dependency (activation... 

Reaction rates are influenced not only by the activation energy and the temperature, but also by the concentrations of the reactants. When there is only one educt, A (1), v is proportional to the concentration [A] of this substance, and a first-order reaction is involved. When two educts, A and B, react with one another (2), it is a second order reaction (shown on the right). In this case, the rate v is proportional to the product of the educt concentrations (12 mM at the top, 24 mM in the middle, and 36 mM at the bottom). The proportionality factors k and k are the rate constants of the reaction. They are not dependent on the reaction concentrations, but depend on the external conditions for the reaction, such as temperature. 

The rate of cell growth is influenced by temperature, pH, composition of medium, rate of air supply, and other factors. In the case that all other conditions are kept constant, the specific growth rate may be affected by the concentration of a certain specific substrate (the limiting substrate). The simplest empirical expression for the effect ofthe substrate concentration on the specific growth rate is the following Monod equation, which is similar in form to the Michaelis-Menten equation for enzyme reactions ... 

Several factors must be considered when the experimental assay condi tions are developed. The reaction rate depends on the concentrations ol substrate, enzyme, and necessary cofactors. In addition, the reaction rate is under the influence of environmental factors such as pH, temperature, anti ionic strength. Enzyme activity increases with increasing temperature until the enzyme becomes denatured. The enzyme activity then decreases until all enzyme molecules are inactivated by denaturation. During kinetic mea surement, it is essential that the temperature of all reaction mixtures lx maintained constant. 

The thermal decay process of the radicals is a bimolecular reaction. The decay rate increases with increasing temperature. At 100° C, a half-life of 12 minutes has been observed for methyl methacrylate popcorn radicals. A fast decay rate takes place when the dry popcorn is swollen in a liquid such as benzene. That means that during the proliferous growth process, when the polymer is swollen by the monomer, a decay process also occurs, and a stationary radical concentration in the growing polymer popcorn results. A liquid that does not swell the polymer (for example, methanol for polystyrene) does not influence the decay rate. A much higher rate of radical decay is obtained with a benzene solution of diphenylpicrylhydrazil. The reaction rate between the polymer radical and inhibitor radical may be measured. 

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