Hess' Law

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Hess’ Law: Heats of Formation for the Formation of Magnesium Oxide and Calcium Oxide

Spandana Amarthaluru
410178
Ms. Longworth
Friday March 22nd, 2013
Data Collection

For calculation purposes, the quantitative data for acquired for the experiments pertaining to equations 1, 2, 4 and 5 is included below. For the full qualitative and quantitative data recorded during the conduction of equation 2, see the attached sheet. Equation 1

Table 1
Time ± 0.1 Seconds| Temperature ± 0.5°C|
| Trial 1| Trial 2|
20.0| 32.0| 30.5|
40.0| 32.0| 30.5|
60.0| 32.0| 30.0|
80.0| 31.5| 30.0|
100.0| 31.0| 30.0|
120.0| 31.0| 30.0|
140.0| 31.0| 29.5|
160.0| 30.5| 29.5|
180.0| 30.5| 29.5|
200.0| 30.5| 29.0|
220.0| 30.0| 29.0|
240.0| 30.0| 29.0|
260.0| 30.0| 29.0|
280.0| 29.5| 29.0|
300.0| 29.5| 29.0|

Equation 2
Table 2
Time ± 0.1 Seconds| Temperature ± 0.5°C|
| Trial 1| Trial 2|
20.0| 40.0| 39.0|
40.0| 43.0| 41.0|
60.0| 44.0| 42.0|
80.0| 44.0| 43.0|
100.0| 42.0| 43.0|
120.0| 41.0| 42.0|
140.0| 42.0| 42.0|
160.0| 42.0| 42.0|
180.0| 42.0| 42.0|
200.0| 42.0| 41.5|
220.0| 43.0| 42.0|
240.0| 43.0| 42.0|
260.0| 42.0| 42.0|
280.0| 42.0| 42.0|
300.0| 42.0| 42.0|
Equation 4
Table 3
Time ± 0.1 Seconds| Temperature ± 0.5°C|
| Trial 1| Trial 2|
20.0| 35.0| 35.5|
40.0| 35.0| 35.0|
60.0| 34.5| 35.0|
80.0| 34.5| 35.0|
100.0| 34.5| 34.5|
120.0| 34.0| 34.5|
140.0| 34.0| 34.0|
160.0| 33.5| 34.0|
180.0| 33.5| 34.0|
200.0| 33.5| 33.5|
220.0| 33.0| 33.5|
240.0| 33.0| 33.0|
260.0| 33.0| 33.0|
280.0| 32.5| 32.5|
300.0| 32.5| 32.5|

Equation 5
Table 4
Time ± 0.1 Seconds| Temperature ± 0.5°C|
| Trial 1| Trial 2|
20.0| 27.0| 25.0|
40.0| 34.0| 30.0|
60.0| 37.0| 33.0|
80.0| 39.0| 36.0|
100.0| 39.0| 37.0|
120.0| 39.0| 37.0|
140.0| 39.0| 37.0|
160.0| 38.0| 37.0|
180.0| 37.0| 37.0|
200.0| 38.0| 37.5|
220.0| 38.0| 37.0|
240.0| 38.0| 37.0|
260.0| 38.0| 37.0|
280.0| 38.0| 36.0|
300.0| 38.0| 36.0|
Data Processing
Equation 1

Step 1: Determine t2 through extrapolation
As the coffee-cup calorimeter used during the experiment was not perfectly sealed, some heat was lost to the environment. Hence, a graph was used to extrapolate the final temperature to be used in determining ΔT for both trials 1 and 2 while conducting the reaction pertaining to equation 1. This is shown in Figure 1 below.

Using the data plotted in Figure 1, the equation of the trend line of the graph was calculated. In determining the slope of the trend line for the graph, t2 was determined as it is equivalent to the y-intercept of this line. Trial 1

Initially, the slope of the line itself was determined.
Point 1:20.0, 32.0, Point 2:(300.0, 29.5)
m=y2-y1x2-x1
29.5°C-32.0°C300.0 sec-20.0 sec
m= -8.93 ×10-3 ℃/sec

The slope was subbed into the y=mx+bequation using Point 1 as a reference point in order to determine the y-intercept of the line. y=mx+b
32.0℃=-8.93 ×10-320.0+b
b=32.2℃
Hence, it was determined that t2= 32.2 ± 0.5°C.
Trial 2
With (20.0, 30.5) and (300.0, 29.0) as reference points, the same procedure was used with the Trial 2 data to determine the final temperature during Trial 2 as 30.6 ± 0.5°C. The trend lines for both trials are plotted on Figure 1. The extrapolations used to determine the final temperatures of the trials are denoted by the dotted line. Step 2: Calculate heat of surroundings (Qsurroundings)

Using the calculations from Step 1, the enthalpy of reaction (∆Hrxn) for equation 1 was calculated for the first trial. The first step in doing so is to calculate Qsurroundings. Before employing the formula Qsurroundings=m∙c∙∆T, the values to be subbed into the formula were determined as shown below. m=(VHCl)(δH2O)

m=100.0±0.5...
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