An investigation into the behaviour of mono-di-tri protic acids with a pure metal.

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Investigating advanced reaction rates.

Aim

In this investigation I will examine how certain variables affect the rate of reaction. In particular I will attempt to evaluate the orders of the reactions, and whether this order is confined to a certain concentration range, and also I will aim to approximate the activation energy through observing the effect of temperature on the rate of reaction.

I will be using Magnesium (alkaline earth metal) during all of my reactions and a range of acids. For a successful outcome, careful planning must be undertaken, where preliminary work will be of key importance in determining quantities and ranges of reactants, and temperatures to use, as well as selecting the most appropriate apparatus and laboratory techniques to be used in the full investigation.                                

Theory

In this section I will explain the theoretical chemistry of the variables in my investigation, through my understanding of rates of reactions as well as the use of information from various sources including, books, the internet, and encyclopaedias which will be fully listed at the end of this project.

The rate determining step of a chemical reaction is one which is the slowest, and it is this which is represented in a rate equation. The rate equation cannot be calculated from the balanced chemical equation, but has to be found through experimental procedures. The overall rate equation takes the form of:

        

Rate (mol dm-³ s-1) = K [A]a[B]b[C]c

Where:

[A], [B], and [C] represent the concentration of the reactant in mol dm-³. The indices ‘a’, ‘b’, and ‘c’ show the order of the reaction with respect to each of the reactants A,B, and C. the sum of all the indices is called the overall order of the reaction.

K’ is a constant of proportionality known as the rate constant, and its units depend on the order of reaction. Knowledge of the rate constant has practical use, in that it can often be used to compare rates of reaction at different temperatures, or for comparing the rates of different reactions with similar rate equations.

As shown above, the order of a reaction with respect to a certain reactant is defined as the power to which its concentration term in the rate equation is raised. The rate of reaction is the change in concentration per second, with units mol dm-³.

Temperature

The kinetic energy of particles follows the Maxwell-Boltzmann distribution. Increase in temperature not only increases average kinetic energy of the reactant particles, but also the fraction of particles having kinetic energy higher than the activation energy. Thus, the effective collision frequency increases.

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The activation energy (minimum energy required for a chemical reaction to occur) for the reaction between Magnesium and Hydrochloic acid will be measured, through obtaining values for the rate at different temperatures. From this a graph of ln(k) against 1/T (Kelvin) will be plotted and the gradient will be calculated, which with the Arhenius equation ( explained in the analysis section), the activation energy will be calculated.

 

The reaction rate for a reactant or product in a particular reaction is defined as the fraction of the chemical that is formed, or removed in moles per unit time ...

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