Enthalpy Change For Deltah 2 example essay topic

Evaluating An Enthalpy Change That Cannot Be Measured Directly. Dr. Watson. Introduction. We were told that sodium hydrogen carbonate decomposes on heating to give sodium carbonate, water and carbon dioxide as shown in the equation below: - 2 NaHCO 3 (s) Na 2 CO 3 (s) + H 2 O (l) + CO 2 (g) = DeltaH 1 This was given as deltaH 1 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 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 500 ml Beaker. 1 x Thermometer (-10 to 50 oC).

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.

Diagram. Method. 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 hydrogen carbonate 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. Calculations. From these results I had to calculate deltaH 2 and deltaH 3. DeltaH 2 refers to the enthalpy change when sodium hydrogen carbonate reacts with hydrochloric acid, and deltaH 3 is the enthalpy change when the sodium carbonate reacts with the acid.

Firstly however it is necessary to show the equations for the two reactions: -DeltaH 2 = 2 NaHCO 3 (s) + 2 HCl (aq) 2 Na Cl (aq) + 2 H 2 O (l) + 2 CO 2 (g). DeltaH 3 = Na 2 CO 3 + 2 HCl (aq) 2 Na Cl (aq) + H 2 O (l) + CO 2 (g) The enthalpy changes of the two reactions can be worked out using the formula shown below: -Energy Exchanged between = Specific Heat Capacity x Mass of the x Temperature Reactants and Surroundings of the Solution Solution Change. Therefore the DeltaH 2 of the reaction when fitted into the formula is: -Energy Exchanged between = 4.18 x (84 x 2) x -11.1 Reactants and Surroundings. This gives the enthalpy change for DeltaH 2 to be = -7794.9 Joules per mole. The same formula is used for DeltaH 3: -Energy Exchanged Between = 4.18 x 106 x 21.8 Reactants and Surroundings.

This gives the Enthalpy change for DeltaH 3 to be = 9659.1 Joules per mole. From these two results we are able to work out what DeltaH 1 is likely to be even though we have not done the experiment. This is done using the formula: - DeltaH 1 = DeltaH 3 + DeltaH 2 = DeltaH 1 = 9659.1 + (-7794.9) = DeltaH 1 = 1864.2 Joules per mole. Conclusions. The result obtained will not be a very accurate due to the means by which the experiment was done. The equipment used was not the most efficient for measuring enthalpy changes, however it does give a rough estimate to work from.

Some errors of the equipment would have been heat lost through conduction from the reaction vessel. Also heat may well have been lost through the open top of the container, even though there was a lid this was not very secure some heat will have escaped through here. In summation the experiment was very difficult to undertake as the enthalpy change for DeltaH 1 is hard to determine due to the fact that it thermally decomposes in the air, causing great problems in calculating its enthalpy change with its surroundings.