Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

3 APPARATUS 23A simple dilatometer merely consists of a glass bulb fused to a length of precisionbore capillary tubing. Good thermostatting is necessary, and care must betaken with a process having a high heat of reaction that heat exchange is efficient;a dilatometer of annular design may be used. When calculating the degree ofreaction from the volume change, it is usually adequate to assume that themolar volumes of reactants and products are additive, but the possibility thatthey may vary appreciably with concentration should be borne in mind.(f) Liquid systems involving dissolved gasSome reactions in solution involve dissolved gas, e.g. oxygen, as one of the reactants,or a gas as a product. In such cases, the process may be conveniently followedby measuring at constant pressure the volume either of reactant gas absorbed,or of product gas evolved, by means of a gas burette connected to the thermostattedreaction vessel, usually with a device for shaking or stirring the solution8lb.Care must be taken to ensure that the rate of absorption or evolution of gasis governed by the rate of reaction and not by the rate of, say, dissolution. This canbe done, for instance, by using conditions under which the rate of absorption isindependent of the rate of shaking.3.2.2 Flow method(a) Someflow systems“Straight through” system. In the simplest case (Fig. 15) the reactant A, main-LiquklreactantReferences pp. 104-1 I IFig. 15. “Straight-through” flow system. From ref. 66.