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Welcome to our Physics lesson on Does the First Law of Thermodynamics Explain Everything about Thermal Processes?, this is the first lesson of our suite of physics lessons covering the topic of Entropy and the Second Law of Thermodynamics, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
Despite its importance in determining the values of heat, work and internal energy, the First law of Thermodynamics does not provide sufficient answers to everything that happens during a thermal process. In nature, not every thermodynamic event occurs spontaneously although at least theoretically the First Law allows this; rather, most processes have a well-defined order of occurrence. Let's consider a few examples to explain this point.
When we place in contact a hot and a cold object, the heat energy always flows from the hottest to the coldest object. We know this from practice but we are not able to determine the direction of heat flow from the First Law of Thermodynamics. It simply tells us that the heat released by one object equals the heat absorbed by the other.
Ice melts at room temperature absorbing heat energy from surroundings but it never freezes at room temperature by giving off heat to the surroundings and making the room hotter.
A drop of ink diffuses in the entire volume of a glass filled with water but it never concentrates back into a single drop when diffused in water.
If you shake a box with salt and pepper, they mix up but they cannot separate again if you continue mixing up the box.
If you line up 20 pencils in parallel on a table and then shake the table, the order of pencils will be distorted and you will never be able again to align the pencils so regularly.
It is clear that all these processes are one-directional; this means they never occur spontaneously. From here, we can deduce they must obey to any physical law unexplained so far.
You have reached the end of Physics lesson 13.10.1 Does the First Law of Thermodynamics Explain Everything about Thermal Processes?. There are 6 lessons in this physics tutorial covering Entropy and the Second Law of Thermodynamics, you can access all the lessons from this tutorial below.
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