Problem 21 - Chemistry The Central Science In Si Units

Question

(a) Which of the following cannot leave or enter a closed system: heat, work, or matter? (b) Which cannot leave or enter an isolated system? (c) What do we call the part of the universe that is not part of the system?

Step-by-Step Solution

Answer

(a) Matter cannot leave or enter a closed system; (b) Neither heat, work, nor matter can leave or enter an isolated system; (c) The part of the universe not part of the system is called the surroundings.

Step 1: Understanding a Closed System

In a closed system, matter cannot enter or leave the system boundary. However, energy in the form of heat or work can be exchanged across the boundary.

Step 2: Analyzing an Isolated System

In an isolated system, neither matter nor energy (in the form of heat or work) can cross the system boundary. The system is completely isolated from its surroundings without any exchange of matter or energy.

Step 3: Defining Surroundings

The part of the universe that is not part of the system is called the surroundings. In thermodynamics, the system is typically isolated for analysis, and everything outside is considered the surroundings that may interact with the system.

Key Concepts

Closed Systems

A closed system is a fundamental concept in thermodynamics. In such systems, matter cannot enter or exit through the system's boundary.
However, energy is not as restricted. Energy, in the form of heat or work, can flow across the boundary of a closed system. This means that although the mass remains constant, the energy levels within the system can change.
For instance, consider a sealed pot on a stove. The water inside won't leave the pot unless the lid is moved, but the heat from the stove can still enter the pot to increase the temperature of the water.

• This allows for various changes within the system as long as they don't involve a shift in matter.

It's crucial to note the difference between energy and matter in these contexts, as it dictates what types of processes can occur within the system.

Isolated Systems

An isolated system takes the idea of a closed system a step further. In an isolated system, not only is matter unable to move across the system's boundary, but energy in any form (such as heat or work) also cannot cross that boundary.
This means these systems are entirely closed off from interactions with their surroundings.
Imagine a vacuum flask or thermos that is perfectly sealed. In this scenario, no heat escapes or enters, and no matter can be exchanged with the surroundings.

• This makes isolated systems ideal for studying reactions or processes that need no external interference.

Thus, isolated systems are rare in everyday applications but are useful concepts for theoretical scenarios.

System and Surroundings

In thermodynamics, distinguishing between a system and its surroundings is essential. The system comprises the part of the universe that is being studied or analyzed. Everything outside this boundary is termed the surroundings.
Understanding the interaction between these two is key to understanding thermodynamic processes. It's the surroundings that the system exchanges heat, work, or other forms of energy with, except in the case of isolated systems.

• For practical purposes, defining the system clearly at the beginning of any analysis is necessary to set up the scope of observations.

For example, when observing a chemical reaction in a beaker, the chemicals and the beaker constitute the system, while everything else is the surroundings.