What do the terms system and surroundings mean? What is the difference between an isolated system and a closed system? What is the universe in terms of thermodynamics?

An isolated system in thermodynamics is one that stands alone, quarantined from the rest of the universe. Imagine a perfectly insulated container where no heat, light, or sound can escape or enter. In such a system, no transfer of energy or matter occurs with the surroundings. This is an idealized concept because in reality, perfect isolation is tough to achieve. Even the most insulated systems we can create, like a thermos, will eventually experience some form of energy transfer over time.

Understanding the nature of isolated systems is crucial in theoretical scenarios. It allows scientists to simplify calculations by assuming that the system's total energy remains constant since it is unaffected by external factors. This concept is pivotal when discussing the first law of thermodynamics, also known as the law of energy conservation. In an equation, it's represented as \( \Delta E_{system} = Q - W = 0 \) for an isolated system, where \( Q \) refers to heat and \( W \) denotes work.

On the flip side, a closed system is slightly more connected with the rest of the world. Although no atoms or molecules can leave or enter, energy is free to cross the boundary. It's like a pot with a lid on a stove: while the lid prevents the soup's ingredients from spilling out, heat from the stove can still pass into the pot and cook the soup.

A home's heating system is a real-world example of a closed system. Heat can be added through the furnace or taken away through air conditioning, but the air inside the home (assuming no windows or doors are opened) remains the same. This system is often analyzed using the first law of thermodynamics in the form \( \Delta E_{system} = Q - W \), where changes in the system's energy are due to heat transfer \( Q \) and work done \( W \), but mass remains constant. Understanding closed systems helps us design more efficient engines, heating and cooling systems, and even model Earth's atmosphere.

When thermodynamicists speak of the universe, they're not just referring to the vast expanse of stars and galaxies. It’s the all-encompassing term that includes the system being studied and everything around it—its surroundings. This concept is a bit abstract but is crucial for understanding that within this 'universe,' the laws of thermodynamics operate under the assumption that energy and matter cannot magically disappear or appear; they can only be transformed or relocated.

If you mix both the system and surroundings, you get the 'thermodynamics universe.' For instance, if a cup of hot tea (the system) is sitting in a room (surroundings), the 'thermodynamics universe' includes both the tea and the room. According to the conservation of energy, the energy lost by the tea as it cools must be equal to the energy gained by the surrounding air in the room. There's a practical outcome of this: we have energy budgets for isolated areas, like when calculating the energy needs for heating a home or running a refrigerator. In these cases, understanding the thermodynamic universe allows us to predict and control the direction and flow of energy.