Simple question about fixed volume

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In summary, "fixed volume" in thermodynamics refers to the system under consideration, which can include the container and/or the water. The boundaries of the system are determined by what variables are needed to calculate unknown values. In the case of an insulated container, the container is not included in the system when calculating heat changes.
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simple question about "fixed volume"

What exactly does "fixed volume" mean in thermodynamics, for a liquid? Does it mean that the container volume is fixed or that the volume of water is fixed, or that the volume of both the container and the water is fixed?

This is confusing me because if it refers only to the container having a fixed volume, then the volume of water could vary (like if you heat the water) while the volume of the container stays fixed. (for example, you have 1L of water in a 2L container).

This all started from a problem which states: "A sample of hot water is mixed with a sample of cold water in an insulated container of fixed volume..." it says the container is fixed volume, so does that mean the water fits perfectly in the container (no air space at the top?)
 
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The volume, fixed or variable, refers to the system under consideration, just as with any other thermodynamic variable.

The often difficult question is deciding what to include in the system. Since the point of the theory is to use the values of known variables to calculate the values of unknown ones this determines the boundaries of the system.

So if we have a perfectly insulating container and we are calculating heat changes within the system, we don't care about the container as no heat passes through it or to it. So we don't include the container in the system.

Hope this helps

go well
 

1. What is a fixed volume?

A fixed volume refers to a specific amount of space that remains constant regardless of changes in temperature or pressure. It can refer to the volume of a substance or the volume of a container.

2. How is the volume of a substance determined to be fixed?

The volume of a substance is determined by its physical properties, such as its shape, size, and density. These properties remain constant, resulting in a fixed volume for the substance.

3. How does a fixed volume affect the behavior of a substance?

A fixed volume plays a crucial role in determining the behavior of a substance. It affects how the substance responds to changes in temperature, pressure, and other external factors.

4. Can the volume of a substance change even if it is considered to be fixed?

Yes, the volume of a substance can change if the conditions it is subjected to change. For example, if the temperature or pressure increases, the volume of a substance may also increase, but the original fixed volume remains constant.

5. What are some examples of substances with a fixed volume?

Some examples of substances with a fixed volume include solids, such as a brick or a book, and liquids, such as water or oil. Gases, on the other hand, do not have a fixed volume as their volume can change with changes in temperature and pressure.

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