Question

In a thermodynamic study, a scientist focuses on the properties of a solution in an apparatus as illustrated. A solution is continuously flowing into the apparatus at the top and out at the bottom, such that the amount of solution in the apparatus is constant with time. (a) Is the solution in the apparatus a closed system, open system, or isolated system? (b) If the inlet and outlet were closed, what type of system would it be?

Short answer

(a) the solution in the apparatus is an open system. (b) with the inlet and outlet closed, it would be a closed system.

Step-by-step solution

Case (a): With the solution continuously flowing in and out.

In this case, the solution in the apparatus has both mass and energy exchange with its surroundings as it is continuously flowing into the apparatus at the top and out at the bottom. As there is mass and energy exchange with the surroundings, this makes it an open system. So, the solution in the apparatus is an open system.

Case (b): With the inlet and outlet closed.

When the inlet and outlet are closed, there is no mass exchange between the solution in the apparatus and the surroundings. However, in this case, there can still be energy exchange between the system and its surroundings (e.g., due to heat transfer). Since there is only energy exchange and no mass exchange, this makes it a closed system. So, with the inlet and outlet closed, it would be a closed system.

Key concepts

Open System

An open system is one that can exchange both mass and energy with its surroundings. This is like having a door wide open to let things flow in and out. In the context of thermodynamics, an open system sees material, like a fluid or gas, move freely across its boundaries. This means:

• Mass can enter or exit the system.
• Energy can also move in or out, either through heat, work, or other forms of energy transfer.

A common real-world example is a kettle boiling water. As water vapor rises, both mass (the water vapor) and energy (the heat from boiling) leave the kettle. In our exercise, the apparatus with a constantly flowing solution exemplifies an open system. The solution enters through one part and leaves through another, ensuring continuous mass and energy exchange with its surroundings.

Closed System

A closed system is more restrictive compared to an open system. It allows for energy exchange but not mass exchange. Imagine a sealed pot on the stove. While heat can pass through the pot's walls, the soup inside stays put. Features of a closed system include:

• No new mass enters or leaves the system.
• Energy transfer can still occur, such as heat escaping through the pot.

In the given scenario, when the inlets and outlets of the apparatus are shut, mass exchange halts. However, energy can still transit across the boundaries (through heat, for example). Therefore, the system transitions to a closed type. It's like placing a lid over our boiling kettle, stopping the water vapor from escaping, but heat can still be exchanged with the environment.

Mass Exchange

Mass exchange refers to the transfer of mass into or out of a system through its boundaries. This process is possible in open systems, where the system's contents may flow:

• Into the system, increasing its mass.
• Out of the system, decreasing its mass.

For instance, mass exchange occurs when ingredients are added to a soup pot. In our thermodynamic apparatus, when the solution flows in and out, the constant movement of particles exemplifies mass exchange. This allows substances to join or depart, significantly affecting the system's dynamics. Unlike closed systems, where the boundary blocks mass transfer, an open system promotes interactions with its ecosystem.

Energy Exchange

Energy exchange in thermodynamics involves the transfer of energy across a system's boundaries, often seen as heat or work. Whether it's an open or closed system, energy exchange is permissible. Here's what you should know:

• In an open system, energy exchange includes mass carrying energy across the boundary.
• In a closed system, energy exchange might not involve mass transfer. It usually involves heat being absorbed or dissipated.

Think of a radiator transferring heat to warm a room—it’s an example of energy leaving a system. When energy is transferred without mass, like when a sealed cup of hot coffee cools down, it's demonstrating energy exchange. With the apparatus in our study, whether the system is sealed or not, energy is always in play, moving towards a balance or delivering work.