Aim: Investigate any one of the factors affecting the rate of heat loss in a liquid.
Introduction: Heat is a form of energy which flows due to a temperature difference. Heat transfer is a process in which energy in the form of heat energy is exchanged between the materials which are at a different temperature.
Hypothesis: If the volume of the water is increased, then the rate of cooling will be slower, because there are more molecules in greater volume than less volume. Thus, it will take more time to lose the heat energy from all the molecules.
Variables:
Independent- Volume of water
Manipulation of variable: Volume is the independent variable. This we would vary by changing the volume of the water each time in the experiment.
Dependant- Temperature
Manipulation of variable: Temperature is the dependent variable which we would measure the initial temperature and measure each in 30 seconds for 5 minutes in the experiment. .
Constant- Liquid used, Total duration of time, initial temperature of water, surrounding temperature.
Manipulation of variable:
– Liquid used: Using the same liquid is necessary, generally water, so the heat capacity will not vary.
– Total duration of time: The duration of time must be kept constant. We take the readings for each volume of water for a certain period of time.
– Initial temperature of water: The initial temperature of water must be kept constant. This can be kept constant by using the same heated water together at the same time.
– Surrounding temperature: The surrounding temperature must be kept constant by doing the experiment in the same room.
Materials: Calorimeter, Stopwatch, Thermometer, Beaker, Hot water, Paper, Pencil
Diagram:
Initial temperature= 42 C
Temperature (in C) |
|||||||||||
Volume of water (in ml) | 30 sec | 1 min | 1 min 30 sec | 2 min | 2 min 30 sec | 3 min | 3 min 30 sec | 4 min | 4 min 30 sec | 5 min | Rate of cooling [ (Initial- Final temperature)/5 min ] |
50 ml | 42 C | 41 C | 41 C | 40 C | 39 C | 39 C | 38 C | 38 C | 37 C | 36 C | 1.2 C |
75 ml | 42 C | 41.3 C | 41 C | 40.8 C | 40.5 C | 40 C | 40 C | 39.7 C | 39 C | 38.8 C | 0.64 C |
100 ml | 42 C | 41.9 C | 41.8 C | 41.6 C | 41.5 C | 41 C | 40.5 C | 40 C | 39.5 C | 39.3 C | 0.54 C |
125 ml | 42 C | 41.8 C | 41.5 C | 41.3 C | 41 C | 40.5 C | 40.3 C | 40.1 C | 40 C | 39.4 C | 0.52 C |
150 ml | 42 C | 41.9 C | 41.7 C | 41.6 C | 40 C | 39.9 C | 39.8 C | 39.7C | 39.6 C | 39.5 C | 0.5 C |
Discussion of observation:
According to our experiment results, after 5 minutes, we found that rate of cooling for 50 ml hot water was 1.2 C and this is the highest cooling rate of water and the rate of cooling for 150 ml of hot water was the lowest (0.5 C). This shows that for 50 ml, which is the least volume of water, lost its heat the fastest, and for 150 ml, which is the most volume of water, lost its heat the slowest. According to the graph, the lower volume of water (50 ml) has a greater fall in temperature, and so, the graph decreases rapidly. As for the (150 ml), the graph is slowly decreasing, since they don’t have a greater fall in temperature.
Conclusion:
Our hypothesis was if the volume of the water is increased, then the rate of cooling will be slower, because there are more molecules in greater volume than less volume. Thus, it will take more time to lose the heat energy from all the molecules.
From the above observations, it is clearly proven that our hypothesis was correct. The least volume of water (50 ml) has rate of cooling of 1.2 C fall per minute. The most volume of water (150 ml) has rate of cooling of 0.5 C fall per minute. This tells us that the higher the volume, the slower the heat loss.
Evaluation: Our experiment could have been done better and more accurately by doing trials and by taking a longer period of time. We made some mistakes when taking measurements because of parallax error.
Improvements: A more drawback is the human responding system, which is not accurate to milliseconds, affecting the results. Some of the errors can be improved if we get to carry the investigation again.
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I feel that you should perhaps go into more detail surrounding why more molecules causes a substance to cool more slowly. It is not because there is more of the substance as such, but more to do with there needing to be more heat energy in a large amount of substance to heat it to a certain temperature than a lower one. Remember that temperature and heat energy are related but separate, so a large amount of substance has more heat energy to loose to change in temperature than a smaller one. 🙂
There are more factors in heat loss than number of moles of substance. You must consider the heat capacities of the liquid storages, surface area towards the dynamic atmospheric conditions and initial temperatures affecting the collision rate of the molecules of water.