Half life period

Halb-weiss, n. Textiles) half-bleach, -wert-druck, m. half-value pressure, -wertsbreite, /. width at half of maximum intensity (of a spectral line or band), -wertzeit,/. half-life period. -woUe, /. half-wool, union. -woU-farberei, /. union dyeing, -wuste, /, semi-desert. 

Halb-zeit, /. half-life period, -zeitkonstante, /. half-life constant, -zellstoff, n. hemicellu-lose Paper) half stuff, -zeug, n. semifinished or semifabricated product Paper) half-stuff, -zinn, n. = Halbgut. -zirkel, m. semicircle. 

Hence, for e.vo/e propenyl)lithium in THF a free energy of activation of AG 38, c of 17 keal/mol was found, with a half-life period of 8 minutes at this temperature17. 

Dioxin half-life period under photolysis is on glass - 6 days, in methanol - 6 hours, in hexane - 1 hour. [3, 8],... 

Even nowadays the application of radioactive isotopes is the most sensitive method for the analysis of biomolecules or their reaction products. Besides the low detection limits, the replacement of a naturally overbalancing stable isotope by its radioactive analogue does not interfere with the physical or chemical properties of the enzyme (with some exceptions for hydrogens). Figure 6 lists some frequently used radioactive isotopes and their half-life periods. 

The reaction rates can also be expressed in terms of half-life or half-life period. The half-life period is defined as the time required for the concentration of a reactant to decrease to half of its initial value. 

The half-life period tm of a zero order reaction can be calculated with the help of equation (1.19), taking t = ty2 and x = all as... 

Thus, the half-life period of zero order reaction is directly proportional to the initial concentration of the reactant. For example, on increasing the initial concentration by two fold, the half-life period of the reaction would also be double. 

The half-life period for a first-order reaction may be obtained from equation (b) by substituting t = tm when x = all, i.e. 

Thus, the half-life period of a first-order reaction is independent of initial concentration of reactant. Irrespective of how many times the initial concentration of reactant changes, the half-life period will remain same. 

Problem 1.10 The kinetics of a reaction was followed by measuring the absorbance due to a reactant at its A,max at 25°C. The log (absorbance) versus time (min) plot was a straight line with a negative slope (0.30 x 10 2) and a positive intercept. Find the half-life period of reaction. 

Half-life period gives the time T which must elapse for the radioactivity to decay to half its value at any instant and may be obtained by pulling... 

Thus the half-life period of a second order reaction is inversely proportional to the initial concentration of the reactant. 

The half-life period in this case can only be determined if the reactants are taken in stoichiometric amounts. 

Rearranging and integrating, the rate constant and half-life period may be obtained as... 

Therefore, in case of third order reactions the half-life period is inversely proportional to the square of initial concentration. 

If ax and a2 are the initial concentrations of the reactant in two experiments of same reactions and ( 1/2)i and (11/2)2 are the corresponding half-life periods, respectively, then... 

The order n may be calculated with the help of above equation. Again a plot of logarithms of ratio of half-life periods versus ratio of initial concentrations will be linear passing through the origin with a slope equal to (n - 1) and thus the order can be determined from its slope. 

Now half-life period for second order reaction is given as... 

What is meant by half-life period (r1/2) of a reaction. Show that f1/2 < = —for... 

For a gaseous reaction between A and B, the half-life period (t1/2) were measured and data reported are... 

A first-order reaction has the rate constant = 1.0 X 10-4 sec 1at 298 K. Calculate the half-life period of the reaction. 

Derive an expression for the rate constant of a reaction having order n. Also calculate the half-life period. 

Derive a relation between absolute temperature and half-life period for a nlh order reaction. 

As natural biological attenuation occurs, the rate of degradation of the contaminants in the soil can be estimated by calculating their half-lives. At the end of each half-life period, the concentration of the contaminant will be reduced by one half. Beginning with a concentration starting time 0, the sequence then is 1 /2, lU, /8,. .. for each succeeding half-life time period assuming all processes continue uninterrupted. 

Preliminary kinetic investigations of the conversion of pS-157 into pR-157 half-life period at 43 °C 347 min, half-life period at 55 °C 84 min,half-life period at 65 °C 26.4 min, half-life period at 75 °C 10.5 min activation energy (gG ) of the epimerization about 24 kcal moL ( 3)... 

Half-life period of a given radioactive substance is independent of the amount of substance present initially. It depends only on disintegration constant of the element. 

N a (t f -22.7 hrs) biochemically more important because of its shorter half-life period. Shorter half-life ensures attainment of transient equilibrium faster. 

The half life period of a substance is 50 minutes at a certain concentration. When the concentration is reduced to one half of the initial concentration, the half life period is 25 minutes. Order of the reaction, calculated ... 

Since the radioactivity of thorium salts is smaller than that of the minerals, B. B. Boltwood (93) thought that some of the radiothorium must have been lost during the purification process. On the assumption that radiothorium was formed directly from thorium, he computed that the half-life period of the former ought to be at least six years, whereas... 

He found that freshly prepared thorium salts have a normal radioactivity which decreases to a minimum in 4.6 years. He computed that the undiscovered member ought to have a half-life period of five and one-half years, and two chemists at the University of Chicago, Herbert N. McCoy (100) and William H. Ross, later verified this prediction. The new element was at first called mesothorium, but is now known as mesothorium 1 (20, 63), the name having been changed because Hahn... 

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