Order of Reactions occurring in aqueous solutions

In summary, the order of reactions in aqueous solutions refers to the relationship between the concentration of reactants and the rate of the reaction. It can be classified as zero-order, first-order, second-order, or higher, depending on how the rate depends on the concentration of reactants. Zero-order reactions have a constant rate independent of concentration, first-order reactions have a rate proportional to the concentration of one reactant, and second-order reactions depend on the concentrations of either one reactant squared or two reactants. Understanding the order of reactions is crucial for predicting reaction behavior and kinetics in various chemical processes.
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A well known rate of reaction experiment is the reaction between sodium thiosulphate and Hydrochloric acid in which colloidal Sulphur is produced. Over time this obscures a cross placed beneath the reaction vessel. Reaction time can then be measured for various concentrations of thiosulphate.

Plotting 1/t against concentration yields a (more or less) straight line graph and my question is what order of reaction is this ? And how does one derive it ? More generally, how is rate of reaction determined for any particular reaction occurring in aqueous solution ? There are a lot of internet videos showing the thiosulphate practical but none seem to discuss in any depth the theoretical reaction kinetics.
 
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FAQ: Order of Reactions occurring in aqueous solutions

What is the order of a reaction?

The order of a reaction refers to the power to which the concentration of a reactant is raised in the rate law expression. It indicates how the rate of the reaction is affected by the concentration of that reactant. The overall order of a reaction is the sum of the orders with respect to each reactant.

How is the order of a reaction determined?

The order of a reaction can be determined experimentally by measuring the rate of the reaction at different concentrations of reactants. By plotting these data and analyzing the resulting graphs, such as concentration versus rate, one can deduce the order with respect to each reactant.

What is the difference between zero-order, first-order, and second-order reactions?

In a zero-order reaction, the rate is constant and independent of the concentration of reactants. In a first-order reaction, the rate is directly proportional to the concentration of one reactant. In a second-order reaction, the rate is proportional to the square of the concentration of one reactant or to the product of the concentrations of two reactants.

Can the order of a reaction be a fraction or negative?

Yes, the order of a reaction can be a fraction or a negative number. Fractional orders often arise in complex reactions or catalytic processes, while negative orders can occur in reactions where the rate decreases with increasing concentration of a reactant, indicating a reverse or inhibitory effect.

How does temperature affect the order of reactions in aqueous solutions?

Temperature can influence the rate of a reaction and may affect the order as well. Generally, increasing temperature increases reaction rates, but the specific relationship between temperature and order depends on the reaction mechanism and the nature of the reactants involved. Changes in temperature can also alter the activation energy and the rate constants, potentially leading to different observed orders under varying conditions.

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