First Law ΔU = Q − W | Understanding & Math Example

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In summary, the first law of thermodynamics can be expressed as the equation ΔU = Q − W, or Q - W = (U2 - U1), where Q represents heat, W represents work, and ΔU represents the change in internal energy of the system. This equation can also be written in terms of specific quantities, such as mass (kg). However, this equation has limitations, as it does not account for all types of energy and is only applicable to closed systems in thermodynamic equilibrium. Additionally, for PV work, there is a difference between PdV and ##P_{ext}dV##, with the latter representing work done by an external pressure. Overall, the first law of thermodynamics is a fundamental
  • #1
lee123456789
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Homework Statement
write about first law
Relevant Equations
Equation: Q - W = (U2 - U1)
ΔU = Q − W.
Is the non flow energy equation just the first law equation
Im writing about the first law

i write the definition and that the first law equation ΔU = Q − W or can be written as Equation: Q - W = (U2 - U1). Then gave a math example using Equation: Q - W = (U2 - U1) to show the first law. When using a unit of substance it is calculated on a unit of mass bases (Kg).
 
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  • #2
I can't really tell what your question is. If you are supposed to write about the first law, you should probably explain what ##Q## and ##W## and ##\Delta U## mean, and give an example. A simple example would involve heating a quantity of some gas (such as oxygen). If the gas is allowed to expand, then heating it can produce work, as well as changing its internal energy.
 
  • #3
Discuss the limitations on the equation.
1. Difference between closed system and open system
2. What types of energy are omitted from this equation? What would the equation look like if these types of energy were included?
3. What are the limitations on the initial and final states of the system in terms of thermodynamic equilibrium
4. What is the entity conserved by this equation?
5. For the PV work, what is the difference between PdV and ##P_{ext}dV##?
 

1. What is the First Law of Thermodynamics?

The First Law of Thermodynamics is a fundamental principle in physics that states that energy cannot be created or destroyed, only transferred or converted from one form to another. This law is often expressed as ΔU = Q − W, where ΔU represents the change in internal energy, Q represents heat transfer, and W represents work done.

2. How do you calculate the change in internal energy (ΔU)?

The change in internal energy (ΔU) can be calculated by subtracting the initial internal energy from the final internal energy. It can also be calculated using the formula ΔU = Q − W, where Q represents heat transfer and W represents work done.

3. What is the relationship between heat transfer (Q) and work done (W) in the First Law of Thermodynamics?

The First Law of Thermodynamics states that the change in internal energy (ΔU) of a system is equal to the sum of heat transfer (Q) into the system and work done (W) on the system. This means that any energy added to a system through heat transfer or work done will result in a change in the system's internal energy.

4. Can you provide an example of the First Law of Thermodynamics in action?

One example of the First Law of Thermodynamics is a car engine. The fuel in the car's engine is burned, producing heat (Q) and causing the gas to expand and push the pistons, resulting in work done (W). This work done is then used to power the car and move it forward. The change in the car's internal energy (ΔU) is equal to the heat transfer (Q) minus the work done (W).

5. How does the First Law of Thermodynamics relate to the conservation of energy?

The First Law of Thermodynamics is a statement of the conservation of energy. It states that energy cannot be created or destroyed, only transferred or converted from one form to another. This means that the total energy in a closed system will remain constant, even if it changes forms through heat transfer or work done.

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