Use of Enthalpy Changes of Metal Reactions

In this essay, the author

• Explains the use of enthalpy changes of metal reactions to experimentally test the reactivity series of common metals.
• Argues that enthalpy changes of reaction can predict the place of a metal in the metals reactivity series.
• Explains that if the hypothesis is proved correct through experimentation then they can apply it to predict the place of metals they have investigated in the reactivity series.
• Explains that arranging the metals investigated in order of decreasing enthalpy change of reaction and comparing this list with published and accepted data will prove the hypothesis is correct.
• Explains that the enthalpy change of a reaction is the heat evolved when the reaction takes place. all chemical bonds hold heat energy within them.
• Explains that an exothermic reaction would be considered to have a negative enthalpy change because heat energy has been given up into the surroundings.
• Explains their hypothesis based on the understanding that more reactive metals will create more stable compounds on reaction, meaning less energy will be held in their strong and stable bonds.
• Explains that the reaction between lithium metal and copper sulphate is simple and safe, and should be spontaneous with a good number of common metals.
• Explains how they calculate the enthalpy change of the reaction using î” h = m c ( tinitial – tfinal).
• Explains that the independent variable is the choice of metal in the experiment, which changes from experiment to experiment. the dependant variable changes because of the changing metal.
• Explains that uncontrolled variables are aspects over which they have no effective control, such as the ambient temperature in the cup which may change with external temperatures. the surface area of the metal affects the rate of reaction.
• Explains that the faster the reaction, the harder it will be to measure the enthalpy change. metal filings can mitigate this by using the thermometer.
• Explains that the reaction will be conducted in the insulated styrofoam cup to minimise the heat loss to the surroundings.
• Explains how the temperature of the reaction is measured in situ by measuring 25cm3 of copper sulphate into a cup and adding 0.5 g (an excess) of metal to the stopwatch.
• Explains that leaving the cup is responsible for the fall in temperature after this point. it is important to take further readings after the peak temperature has passed.
• Explains that heat loss error will mean that the temperature measured will not take account of all the heat generated by the reaction.
• Explains that they have chosen five metals with which to conduct the reaction. they expect them to react with copper ions on the basis of their standard electrode potentials and cover a reasonable range of the reactivity series.