Three quarter reaction time

Thus the three-quarters life (or any given fractional life) is also independent of concentration for a first-order reaction. Examination of the data shows that the first three-quarters life (time to [A] = 0.237 mol dm -) is about 80 min and by inteipolation the second (lime to [A] = 0.178 mol dm - ) is also about 80 min. Therefore the reaction is first-order and the rate constant is approximately... 

For the decomposition of acetaldehyde at 518 C, CH3CH0 => CH4 + CO, data of half and three-quarter times were obtained for several initial pressures P0, torr, as tabulated. Find the order of the reaction. 

At a temperature of 78° C. the velocity constant whether referred to a unimolecular or a bimolecular reaction diminished with time after an hour rather less than three-quarters of the original metaphosphate remains.6 The product is mainly orthophosphate, as was proved by titration with methyl orange and phenolphthalein, although small quantities of pyrophosphate were formed by a side reaction. The pyro-acid was determined by titration to bromophenol blue in the presence of zinc sulphate, which leads to a complete precipitation of pyrophosphate, the ortho-acid being unaffected, thus... 

The table indicates, for example, that the difference in times between one-half and three-quarters completion divided by the half-life, (tn — will be 0.500 for a zero-order reaction, 1.000 for a first-order... 

When [R], = i[R]o half the reactant has undergone reaction and the half-time is equal to In Ifk. This half-time is independent of the concentration, and thus it takes the same length of time for a reaction to go from half to three-quarters completion as it does to go to half completion (Figure 21-1, right). 

For a reaction of this type, the reaction will slow down as the reaction proceeds, so that when half the starting compound has been used up, the rate will have fallen to half of the original value. After three-quarters has been used up (and only a quarter remains), the rate will have fallen to a quarter of the original rate, and so on. The time taken for the concentration to drop to a half of the original value in a first-order reaction is a constant, the half-life this does not depend on the original concentration. 

The supernatants were concentrated with CF 25 cone, washed twice with 1.0 ml buffer, and reacted with a reaction mixture containing 0.5 n mol/I hypoxanthine at 37°C for 30 minutes. Uric acid product was determined by the rate of increased absorption of 293 nm at 37°C measured in a Gilford 2400 type recording spectrophotometer. Protein concentration of the specimens was determined by the Lowry method. Urinary oxypurines were assayed by HPLC as follows. One to two ml of urine samples from 24 hours total excretion were diluted 5-10 times with 0.9% NaCl and filtrated by a 0.45 pm Millipore filter. Three quarters of ml of this sample with 0.25 ml of 0.1 N NaOH and 1.0 ml of ethyo-acetate n- Butanol =2 1 solution were mixed for one minute. 

In a i-l. three-neck flask fitted with a mechanical stirrer, reflux condenser and separatory funnel, are placed 381 g. (1.5 moles) of iodine and 400 g. (5.1 moles) of benzene. The mixture is heated to about 50° on a water bath and 275 cc. of nitric acid (sp. gr. 1.50) is added slowly from the separatory funnel the time required for the addition should be about one and one-quarter hours. A copious evolution of oxides of nitrogen takes place, and the gases are carried off from the upper end of the condenser to an open window or hood. The reaction proceeds smoothly (Note 1) and the temperature rises slowly without the application of heat until the mixture boils gently. When all of the nitric add has been added, the solution is refluxed for about fifteen minutes. If iodine still remains, more nitric add should be added slowly to the warm solution until the purple color of the iodine has been discharged and the solution becomes brownish red. 

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