Evaluating an Enthalpy Change That Cannot Be Measured Directly.

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  • Topic: Hydrochloric acid, Carbon dioxide, Sodium bicarbonate
  • Pages : 3 (664 words )
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  • Published : October 8, 1999
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Evaluating An Enthalpy Change That Cannot Be Measured Directly.

Dr. Watson.


We were told that sodium hydrogencarbonate decomposes on heating to give sodium carbonate, water and carbon dioxide as shown in the equation below:-
2NaHCO3(s)--------> Na2CO3 (s) + H2O (l) + CO2 (g) = DeltaH1

This was given as deltaH1 and we had to calculate as part of the experiment. This however cannot be measured directly, but can be found using the enthalpy changes from two other reactions. These being that of sodium hydrogencarbonate and hydrochloric acid and also sodium carbonate and hydrochloric acid.

We were given a list of instructions in how to carry out the experiment, which are given later.

List of Apparatus Used.

1 x 500ml Beaker. 1 x Thermometer(-10 to 50oC). 1 x Polystyrene Cup. 1 x Weighing Balance. 1 x Weighing Bottle. 10 grams of Sodium Hydrogencarbonate. 10 grams of Sodium Carbonate. A bottle of 2 molar HCL.



Three grams of sodium hydrogen carbonate was weighted out accurately using a weighting bottle and a balance. Then thirty centimetres cubed of 2 molar HCL was measured using a measuring cylinder. The acid was then placed into the polystyrene cup and its temperature was taken and recorded using the thermometer. The pre-weighted sodium hydrogencarbonate was then added to the solution, and the final temperature was recorded.

The contents of the cup were then emptied out and the cup was washed out with water and then thoroughly dried. This was done three times for the sodium hydrogen carbonate so that I could remove any anomalies that were obtained.

The experiment was then repeated in exactly the same manner except sodium carbonate was used instead of sodium hydrogen carbonate.

The results were then tabulated, this table is shown below.

Results Table. Results Table for Sodium Hydrogencarbonate.

Results Table for Sodium Carbonate.


From these results I had to calculate...
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