Investigating displacement reactions to find out the order of reactivity of some metals.

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Aim

Investigating displacement reactions to find out the order of reactivity of some metals. I will find this out by comparing temperature rise caused by different metals during displacement reactions in a salt solution.

Prediction

I predict that the reactivity series for these three metals (Zinc, Magnesium, Iron) will look like this:

Magnesium

Zinc

Iron

I also think the following:

Magnesium will have the most vigorous reaction and the temperature change for this metal will be the most. Zinc will have a vigorous reaction with the solution but it will not be as vigorous as the reaction Magnesium will have. Iron will have the least vigorous reaction, as it is closest to Copper in the reactivity series (when compared with Zinc and Magnesium). Therefore the displacement reaction will occur between Iron and the Copper Sulphate solution but it will not be as significant as the displacement reaction Zinc and Magnesium will have with the Copper Sulphate solution.  

I believe that the most energy will be released by Magnesium. Magnesium as you can

see by the use of the reactivity series is above the other metals I am investigating (Zinc and Iron), meaning it has the ability to loose it’s electrons most easily and displace the copper from the solution and make it a pure metal. The equation for this will be:

Mg + CuSO4            MgSO4 + Cu

I also believe that the reactions will decrease in energy loss as the metal in the reactivity series goes down.

Background Information

To be able to produce our reactivity series, we must make use of the fact that a more reactive metal will displace a less reactive metal from its salt solution. When this happens, heat energy is released, as the reaction is an exothermic one. The greater the difference in reactivity between the two metals, the more energy released. This fact allows us to measure the temperature rise and judge from that which metals are the most reactive and which the least.

The reactivity series is a table of metals with the most reactive metals at the top of the table and the least reactive metals at the bottom. Look below for the reactivity series:

 

A displacement reaction is an example of a redox reaction. In a redox reaction one reactant loses electrons (oxidation) while the other gains the electrons (reduction). For example Zinc metal will displace Copper ions from solution because Zinc is higher than Copper in the electrochemical series. Zinc ions and Copper atoms (metal) are formed - the Zinc atoms lose electrons while the Copper ions gain the electrons.

Every reaction involves energy changes. In order for a reaction to take place old bonds need to be broken and new bonds need to be formed. This involves energy.

To break bonds, energy is needed. This is why many reactions need to be heated to get them started. Those that happen at room temperature are still using the heat from the surroundings to get started; they just don't need as much. The process of breaking bonds is endothermic (needs heat). When bonds are made, energy is released. This is an exothermic reaction (heat is given out).

The bond breaking which will occur will be caused by the displacement reaction ripping apart the bonds between the Copper cations and the Sulphate anions (as we are looking at Copper Sulphate) and because breaking bonds requires energy, the temperature of the reaction will fall. However, the more reactive metal will then make bonds between it and the Sulphate anions, making for a release of energy, which we will see as a rise in temperature. As the energy released by the making of the bonds will be greater than that of the energy taken in to break the bonds, we will note that displacement reactions cause an increase in temperature.

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The more reactive the metal, the stronger the bonds it will make to the sulphate anions, and the more energy will be released when the metal forms those bonds. Thus energy given out by the reaction is proportional to the bond strength.

In a reaction such as Copper Sulphate and Zinc, the Zinc is more reactive than the Copper. As a result, it acts a bit like a bully, demanding that the Copper give it the Sulphate ions. Energy is needed to break the bonds between the Copper ions and the Sulphate ions. When the Zinc bonds ...

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