THERMAL HEATING

Gentiana Spahiu

There are multiple ways for students to learn theories, techniques and other information they would eventually need in their lives and I believe that the best way of teaching is through demonstration and student activities. The chapter of Lab experiments continues with yet another demonstration of things we know just because we are told of them. And yet again we have the chance to actually perform and witness different dynamics of substances, events, and chains of actions and reactions.
The Lab on Thermal Heating would inform us on the amount of energy absorbed by various liquids with different characteristics when heat is involved. (A copy of the lab in word format: Thermal Heating Lab)

For this experiment we were provided with two 100 ml beakers where one contained 80 ml of water and the other carried 80 ml of vegetable oil, both of room temperature. We were also given a hot plate (something similar to what they used to cook a while back) and two temperature probes. Last but definitely not the least, we were provided with access to our constant companions of these labs:  NXT Motor and LabView application. To conduct the experiment the professor pointed out the famo

us formula of the day would be:

ΔE=m c ΔT= volume c ΔT

where :

Δ E: Amount of energy absorbed (J)

m: mass of a liquid (g)

c: Heat capacity: (J/g-K)

ΔT : change in temperature (K)

r: mass density (g/ml)

Looking at the formula and at the experiment instructions we realized that some prep work was needed. First we plugged the hot plate and set it to 1.5 to warm up. Then the formula required that we researched the internet to find the heat capacity (c) and mass density (r) of both water and oil.

GOOD TO KNOW:
– Heat capacity or Thermal Capacity: the measurable physical quantity that characterizes the amount of heat required to change a body’s temperature by a given amount. It is usually measured in Joules per Kelvin.

– Mass Density: material’s mass per unit volume.

WATER	OIL
22.351101	20.32272
22.351101	20.22076
22.351101	20.22076
22.250099	20.22076
22.250099	20.42462
22.250099	20.628241
22.351101	20.83165
22.351101	20.933281
22.452049	21.23786
22.552971	21.339279
22.65386	21.64328
22.85552	21.74452
ΔT= 0.504419	ΔT= 1.421

So, we found:
Coil = 2 J/K r oil = .92

C water = 4.184 J/K r water= 1

On with the Experiment……
Once the hot plate was warmed enough we placed the two beakers of liquids on it and inserted a temperature probe in each of them without touching the glass walls. We then ran the LabView application for a preset time of two minutes to gather the temperature changes in the liquids and record them on an Excel Sheet.
The findings are shown in the table.

Interestingly, when looking at the table we see that the water starts off with slightly a higher temperature than the oil, but as both liquids are warming up and the temperatures are increasing I noticed that Oil was warming up more than water (as expected). When the two minutes were up, the water still had a higher temperature but in terms of temperature oil had absorbed more heat. I found that many were confused on why the water had a higher temperature at the end and I guess we can attribute that to the fact that water initially had a higher temperature to start with. Meanwhile we need to pay attention to the change of temperature in both liquids. In our experiment such change was (initial temp- ending temp.):

ΔTwater= 0.504419

ΔToil= 1.4218

Clearly the oil’s temperature changed the most. Now that we have all the elements needed to plug in the formula we can calculate the energy absorbed by both liquids:

ΔE _water = 168.84 J

ΔE _oil= 209.29 J

We were then required to calculate the percent error for the experiment and possible the source of it. To compute the error percentage we used the formula:

ΔE _water– ΔE _oil|/Average(ΔE _water, ΔE _oil) 100%  = 21.4%

The result of 21.4% I thought it was relatively decent considering the human error in conducting the experiment. Other reasons why such error occurred could be the fact that the initial temperatures of the liquids were different (very relevant), the problem our group had with heating up the hot plate and moving the beakers around before we finally inserted the temperature probes (to emphasize here- We never let the probes touch the glass walls).

Conclusion:

As expected the oil heat up faster than the water and this is due to the different characteristics that materials and liquids have. Such knowledge helps people to better define the kind of materials they would use for different projects. A person who is thinking of building a house will certainly consider the different building materials (wood, bricks, or glass) not only in terms of cost but even in terms of heat absorption and retention.