Read full version paper The Specific Heat Capacity Of A Liquid By The Method Of Cooling
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Autor: antoni 30 March 2011
Words: 1597 | Pages: 7
This experiment will be using the calorimeter to measure the specific heat capacity of paraffin and water by the method of cooling. Specific heat capacity is to measure the heat energy required to increase the temperature of a unit quantity of substances by a certain temperature interval and is the S.I unit is J g-1K-1. Thus, heat is measured by monitoring the temperature difference between heat transfer fluid and process fluid. Also, using calorimeter in this experiment is because we need to measure the heat of chemical reactions or physical changes as well as heat capacity. Firstly, a blackened copper calorimeter with copper lid to fit is bored with two holes to take a thermometer (0-100。C in 0.1.C) and a copper stirrer. Secondly, the outer jacket should place in double-walled and should fill with a mixture of water and ice. The lid of the calorimeter is to reduce heat losses by the process of convection and evaporation. As for theory, it used to determine the formula of
[ m0c0+(m1-m0)c ] t1
Lastly, hypothesis of this experiment is the differences of the specific heat capacity have difference duration of time to cool down. Therefore, water has higher capacity then paraffin oil; it needs to take a longer time to cool down in a constant temperature, 40.C.
To determine the relationship of the specific heat capacity and the time taken to cool down in between of water and paraffin oil.
1. Firstly, weight the mass of the calorimeter with the lid and the stirrer.
2. Secondly, assemble the apparatus follow as in the diagram and meanwhile heat up
the water in a beaker to about 70.C.
3. Thirdly, the calorimeter is removed from the apparatus and it is filled with 125ml of heated water in it to within a centimeter of the top. Thermometer, stirrer and lid is replaced and put the whole back in to the cooling chamber (double-walled contained the mixture of ice and water).
4. Water was stirred frequently; when the temperature decrease to 60.C, record the temperature in one minute intervals down to 40.C by using a stopwatch.
5. Thermometer is removed and the calorimeter and its contents, including the lid and the stirrer need to re-weight the mass of it.
6. Result of the first experiment is recorded in the table.
7. Then, the calorimeter is rinsed with water and wiped it till dry.
8. Later on, heated up the paraffin oil in a beaker to about 70.C and poured 125ml of it into the calorimeter.
9. As same as the first experiment, keep on stirred the paraffin oil and record down the temperature when it decrease to 60.C in one minute intervals down to 40.C by using a stopwatch.
10. Thermometer is removed and the calorimeter and its contents, including the lid and the stirrer is re-weighted.
11. Lastly, all the result was recorded in the table and draws a graph to show the differences of the specific heat capacity have difference duration of time to cool down.
Mass of calorimeter + lid + stirrer m0 = 224g = 0.224kg
Mass of calorimeter + lid + stirrer + paraffin oil m1 = 312g = 0.312kg
Mass of calorimeter + lid + stirrer + water m2 = 340g = 0.340kg
Table 1: Water
Table 2: Paraffin Oil
Co= 3.8x102 J.kg-1K-1
Cw = 4.2x103 J.kg-1K-1
m0 = 0.224kg
m1 = 0.312kg
m2 = 0.340kg
tw = 17.5 min (water)
t1 = 10(paraffin oil)
01 = 55°C
02 = 45°C
For method 1:
The average rate of cooling for the calorimeter and liquid contents is
[(0.224)(3.8x102) + (0.312-0.224)C][45-55]
Average rate of cooling is
=[(0.224)(3.8x102) + (0.312-0.224)C][45-55]
Two average rates of loss of heat must be equal. Hence,
[moco+(m1-m0)c][02-01] = [moco+(m1-m0)c][02-01]
Therefore, [moco+(m1-m0)c] t1
(0.224)(3.8x102) + (0.312-0.224)C 10
(0.224)(3.8x102)+(0.340-0.224)(4.2x103 J.kg-1K-1) 17.5
0.088C 241.92 C 2.7x103 J.kg-1K-1
The rate of cooling of the calorimeter and contents must be the same in both cases, hence,
[moco+(m1-m0)c] x M1 = [moco+(m2-mo)cw x Mw
Mw = 42-50 Ml = 44-54
= -0.52 = -0.83
[(0.224)(3.8x102)+(0.312-0.224)C]x-0.83 = [(0.224)(3.8x102)+(0.340-0.224)(4.2x103] x-0.52 85.12+0.088C(-0.83) = 85.12+0.116(4.2x103) x-0.52
85.12+0.088C = -168.224
0.088C = -253.344
C = 2.9x103 J.kg-1K-1
Average values for C:
C in method 1 = 2.7x103 J.kg-1K-1
C in method 2 = 2.9x103 J.kg-1K-1
Therefore, the average values for C is
= 2.7x103 J.kg-1K-1 + 2.9x103 J.kg-1K-1
= 2.8x103 J.kg-1K-1
Based on the sources of engineering tool box (http://www.engineeringtoolbox.com/specific-heat-fluids-d_151.html), the actual value of the specific heat capacity of paraffin oil should be 2.13x103 J.kg-1K-1.. C in method I that I have done is 2.7x103 J.kg-1K-1 and C in method 2 is 2.9x103 J.kg-1K-1. So, the average values for C is 2.8x103 J.kg-1K-1. The different between these two values of specific heat capacity is 0.62x103 J.kg-1K-1.
Moreover, there were some possible sources of error when we doing this experiment because the experimental value of the specific heat capacity is different from the actual value. One of the reasons is parallax error, it wills occurs in error reading of an instrument employing a scale and pointer. This is because the observer's eye and pointer are not in a line perpendicular to the plane of the scale when we took the reading of the paraffin oil and water. If this occurs, the reading of the temperature in paraffin oil and water will be affected. Therefore, the specific heat capacity of the paraffin oil, C, was appeared differently.
On the other hand, environmental factors are one of the systematic or random errors. Before starting to do the experiment, we should off the fan. If not, it will cause vibrations and changes in temperature. Also, the liquid of paraffin oil and water will evaporate easily and it will affect the time taken of the experiment. Thus, human error should also be avoided in error analysis discussions because it is too general to be useful. Sometimes human may cause carelessness and poor technique on the part of the experimenter.
In these two parts of the experiment, it is very important to have the same volumes of liquid in paraffin oil and water. We should beware of heating beyond the recommended temperature of 70° as it is inflammable. So, the internal energy of a system depends only on its state; any increase in the internal system is the sum of the heat supplied to the system and the work done on the system. When you were stemming the water or paraffin oil, internal energy and heat is produced. As well as, internal energy is the sum of all the microscopic kinetic and potential energies of the molecules in an object. Also, heat is energy transferred as a result of a temperature gradient.
In conclusion, precautions should be taken to reduce the error which will cause the changes to the final result. We should be careful when we place our eyes position to the meniscus level of the mercury when we taking the reading from the thermometer. Also, we should prevent environmental factors and human error while doing the experiment.