Quick question 1st law thermodynamics

In summary: Therefore, the total change in internal energy is always 0. In summary, the equation to find the change in heat of a system that is isothermal is \Delta Q = P\Delta V and the total change in internal energy for a PV graph where the state of the system loops back onto itself is always 0.
  • #1
ice87
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What is the equation to find the change in heat of a system that is isothermal?

And also, for a PV graph, if the state of the system loops back onto itself, as in it starts at a and ends at a, is the total change in internal energy always 0?
 
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  • #2
ice87 said:
What is the equation to find the change in heat of a system that is isothermal?
Since PV=nRT, if T does not change, PV is constant. So the internal energy of the system does not change. As a result, there has to be heat flow to or from the system when work is done by or to the system (if it is compressed, heat is lost to the system; if it expands isothermally, it absorbs heat). The heat flow is: [itex]\Delta Q = \Delta U + P\Delta V = P\Delta V[/itex].

And also, for a PV graph, if the state of the system loops back onto itself, as in it starts at a and ends at a, is the total change in internal energy always 0?
Yes. If PV is the same, T is the same (PV=nRT). Since [itex]U = nC_vT[/itex], if the temperature is the same and n does not change, internal energy is the same.

AM
 
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  • #3


The first law of thermodynamics states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. This can be represented mathematically as ΔU = Q - W.

For an isothermal process, the temperature of the system remains constant. Therefore, the change in internal energy (ΔU) is equal to 0. This means that the equation to find the change in heat (Q) for an isothermal process is simply Q = W.

Regarding the PV graph, if the state of the system loops back onto itself, the total change in internal energy will depend on the path taken by the system. If the path taken is reversible, then the total change in internal energy will be 0. However, if the path is irreversible, there may be a change in internal energy even if the starting and ending states are the same. This is because irreversible processes involve energy dissipation and are not completely reversible.
 

1. What is the first law of thermodynamics?

The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only transferred or converted from one form to another.

2. How does the first law of thermodynamics apply to everyday life?

The first law of thermodynamics applies to everyday life in many ways, such as the energy we use to power our homes, cars, and electronic devices. It also plays a role in our body's metabolism and the food we consume for energy.

3. What are some examples of the first law of thermodynamics in action?

Some examples of the first law of thermodynamics in action include a car's internal combustion engine converting chemical energy into mechanical energy, a battery converting chemical energy into electrical energy, and the sun's energy being converted into heat and light on Earth.

4. How is the first law of thermodynamics related to the conservation of energy?

The first law of thermodynamics is directly related to the conservation of energy principle, as it states that energy cannot be created or destroyed, only transferred or converted. This means that the total amount of energy in a closed system remains constant.

5. What is the difference between the first and second law of thermodynamics?

The first law of thermodynamics deals with the conservation of energy, while the second law deals with the direction of energy transfer and the quality of energy. The second law states that in any energy transfer or conversion, some energy will be lost as heat and the overall quality of energy decreases.

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