Hess

9 September 2017

& # 8217 ; Law Essay, Research Paper

Hess & # 8217 ; Law: Work to be done: Find enthalpy alteration by mensurating temperature alteration of a reaction. Chemicals and setup: Thermometer Scale Isolator NaOH, solid NaOH, 0.50M solution Acetic acid, 0.50M and 0.25M Lab: Reaction 1 ) The temperature of 200ml H2O that I poured into the isolator was 23.0 & # 186 ; C. To that I added 1.97g solid NaOH and allow the reaction take topographic point. After a piece I measured the temperature to 24.9 & # 186 ; C & # 224 ; rT = 1.9 & # 186 ; C. The figure of mole NaOH is 1.97 / 40 = 0.049 mol. Reaction 2 ) In this experiment I used 100ml 0.50M acetic acid, and to that I added 100ml 0.50M liquid NaOH. The temperature of the acetic acid was 23 & # 186 ; C and the temperature of the NaOH was 22 & # 186 ; C. So the norm, and the figure I use will be 22.5 & # 186 ; C. After the reaction the temperature of the solution was 25 & # 186 ; C, so rT = 2.5 & # 186 ; C. The figure of mole NaOH is 0.50 * .100 = 0.050 mol. Reaction 3 ) In the 3rd reaction I used 200ml 0.25M acetic acid with a temperature of 22.5 & # 186 ; C, that I added to 2.00g NaOH. The

temperature after the reaction was 27?C, so rT = 4.5?C. And the number of mole NaOH in the reaction was 2.00 / 40 = 0.05 mol. The same amount NaOH has been used in all three reactions, and the same amount of liquid also, 200ml. In reaction two and three is also the amount acetic acid the same.I can now calculate the enthalpy changes in each case: H = c m T, and since the same mass has been used, and since I can use the same c in all three cases H = 0.84 T (c = 4.2, m = 0.200g) rH1 = 1.596 rH2 = 2.1 rH3 = 3.78 According to Hess’ Law you should be able to calculate the enthalpy change for a reaction which is the sum of two (or more) reactions with known enthalpy change, so:NaOH(s) a NaOH(aq) (1) NaOH(aq) + HCl a NaCl + H2O (2) NaOH(s) + HCl a NaCl + H2O (3) (3) – (2) = (1) and we can also see that rH3 – rH2 ” rH1 Other results in class: GroupH1H2H3H3-H2 11.262.13.361.26 21.672.33.271.47 36.821.898.46.51 41.262.944.21.26 51.602.13.781.68 61.5962.13.363.36 72.52.14.22.1(The results of group 3 was probably because they isolated more.)

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