Embedded Files
Introduction
Purpose: The purpose of this PBL is to explore the laws of conservation of energy and momentum by investigating how the macroscopic properties of a thermodynamic system such as temperature, specific heat, and pressure are related to the molecular level of matter, including kinetic or potential energy of atoms.
Driving Question: Why does ice melt faster on one ice-melting block than the other?
Hypothesis: The ice melts faster on one ice-melting block because that ice melting block is made of a material with a high thermal conductive capacity.
Materials
Ice-melting blocks with O-rings
Ice, cubed
Timers
Procedure
Place an O-ring on each ice-melting block.
Place a timer beside each ice-melting block.
Select two ice cubes. Ensure that they are similar in size and shape.
Place an ice cube on each ice-melting block.
Once the first ice cube is in place, begin the first timer.
Repeat Step 5 with the second ice cube and its respective timer.
Observe the ice cubes as they melt.
Once one of the ice cubes has melted completely, stop both timers and record the data.
Analyze the data and utilize background knowledge to determine what factors caused the ice cubes to melt at different rates.
Note: This experiment originally called for a recording of the initial and final temperatures of the ice-melting blocks. However, due to the lack of a functioning temperature sensor, these steps were excluded.
Safety
Because of the relatively benign nature of the experiment itself, the only safety precautions that must be observed are the following:
Maintain the work area clean and uncluttered.
Avoid touching any component of the experiment unnecessarily, as body heat may affect the final or starting temperatures of the ice-melting blocks.
Ensure that there are no exposed wires or electrical outlets near the work area, as water is a conductor of electricity.
Action Video & Pictures
Graph
Scientific Principle
The primary scientific principle applied in this PBL is thermodynamics.
The laws of thermodynamics define fundamental physical quantities (temperature, energy, and entropy) that characterize thermodynamic systems. 1
The Law of Conservation of Energy (otherwise known as the first law of thermodynamics) states that energy cannot be created or destroyed in an isolated system.
The second law of thermodynamics states that the entropy of any isolated system always increases.
The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.
The zeroth law of thermodynamics involves some simple definitions of thermodynamic equilibrium. Thermodynamic equilibrium leads to the large scale definition of temperature, as opposed to the small scale definition related to the kinetic energy of the molecules. The first law of thermodynamics relates the various forms of kinetic and potential energy in a system to the work which a system can perform and to the transfer of heat. This law is sometimes taken as the definition of internal energy, and introduces an additional state variable, enthalpy. The first law of thermodynamics allows for many possible states of a system to exist. But experience indicates that only certain states occur. This leads to the second law of thermodynamics and the definition of another state variable called entropy. The second law stipulates that the total entropy of a system plus its environment can not decrease; it can remain constant for a reversible process but must always increase for an irreversible process.2
1 Boundless. “The Three Laws of Thermodynamics.” Boundless Chemistry. Boundless, 02 Jun. 2016. Retrieved 06 Oct. 2016
2"What Is Thermodynamics?" NASA. Ed. Nancy Hall. NASA, 05 May 2015. Web. 06 Dec. 2016.
Data Table
Observations
The ice cube placed on Block #2 melted eight times more quickly than the ice cube placed on Block #1.
Block #2 is much heavier than Block #1, and appears to be made of some type of metal.
Block #2 is cold to the touch, whereas Block #1 appears to be at room temperature.
Despite being timed for nearly fifteen minutes, the ice cube on Block #1 remained only half melted.
Analysis and Discussion
In seconds, the ice cube on Block #1 remained half-melted after 878.53 seconds. The ice cube on Block #2 melted completely after 111.13 seconds. This indicates that the transfer of energy between the ice cube and the block was greater in the case of Block #2. In the case of Block #1, the transfer of energy was sluggish, resulting in a longer melting time.
Conclusion
In conclusion, the answer to the driving question is as follows: The ice cube on Block #2 melted more quickly because that ice melting block was made of a material with a higher thermal conductive capacity.
Real Life Application
Thermodynamics, more specifically the concept of heat transfer, is applicable in many different facets of life. For example, when designing thermal clothing, one must take into account the amount of heat absorbed by certain fabrics, a factor that is defined by its color, density, and the components of the fabrics themselves. Perhaps one of the most obvious examples of thermodynamics in real life can be found in the creation of cooling systems such as refrigerators and air conditioners, objects whose primary function is to lower temperatures. Understanding the laws of thermodynamics allows us to further industry and create effective shelters and cooling and heating systems, all of which facilitate the modern lifestyle.
Investigation Questions
While the ice was melting on each block, was any energy received or transferred from the air to the ice on either block? If yes, was the amount of energy received or transferred from the air greater or less than that from the blocks? How do you know?
Energy was transferred from the air to the ice on both blocks. However, the amount of energy transferred from the air is less than the amount of energy transferred from the block. Both ice cubes were affected by the same ambient temperature in the same location. However, one ice cubes still melted more quickly than the other. This is due to the influence of the energy transferred from the block.
Would the same piece of ice melt faster on the ice-melting blocks if the ice-melting blocks had greater mass but the same thickness? Explain your answer.
The ice would melt more quickly because the amount of energy produced has increased. In accordance with the Law of Conservation of Energy, if more energy is produced, more energy is transferred to the ice. This allows the ice to melt more quickly.
Would the same piece of ice melt faster on the ice-melting blocks if the ice-melting blocks had greater mass and greater thickness? Explain your answer.
No, because the ratio of the thickness and the mass would remain the same. Thus, this hypothetical scenario is the same as the actual experiment. It has simply been enlarged.
Would the same piece of ice melt faster on the ice-melting blocks if the amount of surface area contact between the ice and the blocks was greater? Explain your answer.
No, because points of contact do not affect final melting time. Regardless of the amount of surface area contact, the mass, thickness, and amount of energy produced remains the same.
Imagine you put both ice-melting blocks in the refrigerator overnight before performing the same ice melting demonstration. How would your result be different than that seen when the ice-melting blocks started at room temperature? Explain your answer.
The starting temperature of the ice melting blocks would not affect the final result of the experiment, as the conductive capacity of metal and wood does not change.
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