Comparing Specific Heat of Ethanol and Water
Experiment number : 4343
Goal of Experiment
The goal of this experiment is to compare specific heat capacities of ethanol and water.
Basic information concerning specific heat capacity is listed in the taks Comparing Specific Heat of Water and Vegetable Oil, Theory.
Two identical plastic cups, low container for water, thermal imaging camera, electric kettle, ethanol.
Pour the same mass of water and ethanol into each of the two plastic cups.
Place the containers in the low container and fill it with hot water from the kettle, so that it reaches approx. one quarter of the height of the plastic cups, thus preparing a water bath.
Use the thermal imaging camera to observe how liquids in small cups heat up.
The video below shows a successful execution of the experiment. We can see that the temperature of ethanol increases faster than the temperature of water, which corresponds to the fact that its specific heat capacity is almost half that of water.
In this video, FLIR i7 thermal imaging camera was used. The temperature range of a colour scheme was set in the interval of 23 °C and 47 °C, the emissivity was ε = 0.95.
Pour the hot water into the low container slowly and steadily – if you pour rapidly, you may overturn the cups with the liquids being tested or they may “float away” from the field of view of the thermal imaging camera.
It is useful to point out to students that the thermal imaging camera only senses the temperature of the liquid surface.
To make the experiment conclusive, we require the mass of the heated ethanol and water to be the same; since the ethanol is less dense, its volume will be greater.
It is the different heights of the levels in the containers that leads students to such explanations of the experiment that do not work with specific heat capacity. Quite often, students assume that in the case of the fuller container, the temperature increase will be slower – after all, we heat the containers at their bottom and in the fuller one will therefore take longer for the heated liquid to rise to the surface where we measure the temperature. Such reasoning is to be appreciated, it makes physical sense, and if there was the same liquid in both containers, this explanation would indeed be relevant. The execution of our experiment, however, gives the opposite result – although the volume of ethanol is greater and its surface is therefore higher, it heats up significantly faster than in the case of water; the height of the surface is therefore probably not an essential factor in this experiment.
Link to similar experiment
The above experiment can of course be performed without a thermal imaging camera, with only two temperature sensors. This simpler equipment was used in a related experiment Porovnání měrné tepelné kapacity oleje a vody (in Czech only) which, in addition to the actual comparison of specific heat capacities, contains an extended reflection on the measured temperature versus time dependencies, that may seem paradoxical at first glance.
Thermal imaging camera basics - link to PDF
In this experiment, a thermographic measurement is used. The theory of thermography and basic recommendation and procedures that can help you obtain more accurate and undistorted results can be found in Experiments with thermal imaging camera (in Czech only).