Submitted by: Submitted by johncola19
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Pages: 6
Category: Science and Technology
Date Submitted: 04/15/2013 10:49 AM
Hess’s Law Data Sheet
Data and Observations:
Keep your initial observations and data in your notebook pages. Use the space below to fill in your final answers once you are done.
Determination of Ccal:
| Trial 1 | Trial 2 | Trial 3 |
| Cold Water | Hot Water | Cold Water | Hot Water | Cold Water | Hot Water |
Mass of water (g) | 48.978 | 48.11 | 48.751 | 46.860 | 51.364 | 50.280 |
Ti (C) | 18.7 | 66.8 | 20.1 | 62 | 19.5 | 65 |
Tf (C) | 41.38 | 41.38 | 40.87 | 40.87 | 39.81 | 39.81 |
(Tf – Ti) = T (C) | 22.68 | -25.42 | 20.77 | -21.13 | 20.31 | -25.19 |
qw = m · c · T (J) | 4647.68 | -5116.85 | 4236.54 | -4142.8 | 4364.76 | -5299.26 |
- qHW – qCW | 469.17 | -93.74 | 934.5 |
Ccal (J/C) | 20.69 | -4.5 | 46.01 |
Average Ccal = 20.73 (J/C)
Show an example of the calculations for one trial on the next page.
Determination of Hf for MgO:
[Remember, - qrxn = - n · H°rxn = Ccal · T + (m · c · T) with c = 3.862 J/(g°C)].
Reaction Trial | Mg or MgO (moles) | Total mass of solution (g) | T (C) | qrxn (KJ) | Hrxn (KJ/mol) | Observations |
Mg + HCl Trial 1 | .012 | 49.557 | 22.76 | -4.35 | -362.5 | Bubbles with gas |
Mg + HCl Trial 2 | .012 | 48.815 | 25.19 | -4.75 | -395.8 | Bubbles with gas |
MgO + HCl Trial 1 | .015 | 49.299 | 8.18 | -1.56 | -104 | Bubbling occurred |
| | | | | | |
Ccal example calculation:
Trial 1-
Mass of cup with stir bar- 9.470 grams
Mass of cup with stir bar and 50 mL of water- 58.448 grams
Mass of beaker before heating- 49.163 grams
Mass of beaker with 50 mL of water- 98.293 grams
Mass of beaker with hot water- 97.273 grams
Mass of cold water in grams- Simply found by subtracting the mass of the cup and stir bar alone from the mass of the cup, stir bar and 50 mL of water from:
58.488 grams-9.470 grams=48.978 grams of cold water
Mass of hot water in grams- Simply found by subtracting the mass of the beaker alone from the mass of the beaker with hot water:...