Practical investigations
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Thanks for your last answer! I'm still confused that when I monitor the temperature rise of the Mg-HCl and Mg-CH3COOH reactions (in a waterbath), given that they all react at room temperature. Would the temperature rise in HCl reaction be higher than that in CH3COOH reaction? Would the waterbath, which keeps the temperature constant, make any difference to the temperature rise?
141108
Corrie writes ....
Assuming the reaction between Mg and your two acids both give out the same amount of heat energy (same value for the enthalpy change), I would expect any temperature rise to be greater in the case of HCl because the reaction is much faster. In the case of the much slower reaction with ethanoic acid, the heat energy will not be produced as quickly and there will be more time for it to be lost to the surroundings.
However, the enthalpy change for the two reactions will, as I've explained in a previous answer, probably not be the same, but I do not expect they will be sufficiently different to alter what I've said above about any temperature rise.
The object of using a waterbath, at a given temperature, is to make good thermal contact with the reaction mixture in order to keep its temperaturte constant by exchange of heat energy with the waterbath. Stirring the mixture also plays an important part in ensuring the mixture makes contact with the walls of its container in the waterbath.
So, if a waterbath is doing its job, the temperature of the mixture should not rise significantly - providing the rate of heat release by the reaction is not too great. It would be very difficult to control the temperature of a very fast, very exothermic reaction without special apparatus.
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updated: 19 November 2008
