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An Experiment to Investigate the Kinetics of the Reaction of Magnesium with Acid

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Jason Kotiah 7/9/2000 An Experiment to Investigate the Kinetics of the Reaction of Magnesium with Acid Aim The aim is to find out the kinetics and determine the rate of reaction of magnesium with hydrochloric acid. To do this we have to measure the amount of hydrogen gas being produced within a given time and from this, the order of magnesium and HCl(aq) can be worked out. Also the activation energy can be worked out, by increasing the temperature of the HCl(aq) and from this, measure the amount of hydrogen produced within certain time intervals. Background Theory The collision theory is a model, which has been used to account for the dependence of rate of reaction on temperature. The collision theory involves reacting particles such as HCl(aq) moving towards each other such as magnesium and colliding in such a way that bonds are broken and new bonds formed. In many reactions between gases, it is the actual collision, which controls the rate of the reaction. For a collision which actually results in a reaction, the kinetic energy possessed by the colliding particles of HCl(aq) and magnesium, must be more than a certain minimum energy, E e.g. a mole of colliding particles at a temperature T, the rate of reaction can be found from: ln(rate) = ln(collision rate) - EA/R (1/T) where R is the gas constant, 8.314J K-1 mol-1 and EA is the activation energy. ...read more.


The fraction of particles with energy greater than EA is equal to the shaded area divided by the total area: Experiments (orders) such as this one show that the rates of most reactions can be related to the concentration of individual reactants by an equation of the form: Rate = k(X)n This expression, in which X is the reactant (HCl(aq)) and n is usually 0,1 or 2, it is known as rate equation or rate law. The value of n gives the order of the reaction. When n = 0, the reaction is said to be zero order with respect to HCl(aq): Rate = k[HCl(aq)]0 But, since [HCl(aq)]0 = 1, Reaction rate = k When n = 1, the reaction rate is proportional to [HCl(aq)]1 and the reaction is said to be first order with respect to HCl(aq). When n = 2, the reaction rate is proportional to [HCl(aq)]2 and the reaction is said to be second order with respect to HCl(aq). This graph shows the variation of reaction rate with concentration for reactions, which are zero, first and second order. Overall Preliminary Work The basic principle of this experiment was to add magnesium to HCl(aq) and then measure the rate of the reaction at different time intervals or finding out how long it took for the reaction to finish. To start off the preliminary stages of this experiment, I had to find out what form of magnesium to use: - ribbon, filings or powder. ...read more.


If I were to use 0.1g of Magnesium for the activation energy experiments, then I would have to react this amount of Magnesium at much higher temperatures then room temperature. This would cause problems as the Magnesium would react so quickly that the rate would be near infinity (rate = time). Even with lower concentrations than 2M Hydrochloric acid the problem of not getting results of a large enough time range still remains. Also the amount of Hydrogen gas produced was very small, so to get an end point for all of the reactions (e.g. how long it took to collect 10cm or 20cm) would be impossible. As a result, I chose 0.3g of Magnesium filings. This amount of Magnesium would be used to find both the activation energy of the reaction between Hydrochloric acid and Magnesium and also the order of HCl(aq) in this reaction. The Order of Hydrochloric acid in this reaction with Magnesium Aim: to find the order of hydrochloric acid with respect to its reaction with Magnesium. It is not possible to find the order of Magnesium, because Magnesium is a solid and therefore it's concentration does not change during the reaction. Key variables: concentration of HCl(aq) Control Variables: temperature, amount of magnesium and volume of acid Preliminary work: to calculate the order of HCl(aq), the concentrations needs to be varied. The maximum concentration for Hydrochloric acid for this investigation was 2M and the lowest concentration I decided to use was 0.1M. Lower concentrations of acid reacting with Magnesium would take a lot of time. 4 1 ...read more.

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