ENERGY CHANGES IN SYSTEMS

Introduction

Energy changes can occur in physical and isolated systems, which refer to different types of systems based on their ability to exchange energy with their surroundings. Let’s look at each of these systems in detail.

1) Physical Systems: Physical systems are systems that can exchange energy with their surroundings in the form of heat or work. Examples of physical systems include open systems and closed systems.

Open systems are systems that can exchange both matter and energy with their surroundings. An example of an open system is a pot of boiling water on a stove. Heat energy is transferred from the stove to the pot, and water molecules escape from the pot into the surrounding air.

Closed systems are systems that can exchange energy with their surroundings, but not matter. An example of a closed system is a sealed container of gas. Energy can be added to the gas by heating it, causing the molecules to move faster and increase the internal energy of the system.

In physical systems, energy changes occur due to the transfer of heat or work between the system and its surroundings. These energy changes can be calculated using the first law of thermodynamics, which states that the total energy of a system and its surroundings remains constant. The change in internal energy (ΔU) of a physical system is given by the equation:

ΔU = q + w

where q is the heat transferred to or from the system, and w is the work done on or by the system. If heat is transferred to the system, q is positive; if heat is transferred from the system, q is negative. If work is done on the system, w is positive; if work is done by the system, w is negative.

 

2) Isolated Systems: Isolated systems are systems that cannot exchange energy or matter with their surroundings. Examples of isolated systems include thermally insulated containers and adiabatic systems.

In isolated systems, energy changes occur due to internal processes within the system. The first law of thermodynamics still applies, but because there is no heat or work transferred between the system and its surroundings, the change in internal energy (ΔU) is equal to zero.

ΔU = q + w = 0

This means that any energy changes that occur in an isolated system must be due to internal processes, such as chemical reactions or changes in temperature or pressure.

In summary, energy changes in physical and isolated systems are determined by the transfer of heat or work between the system and its surroundings or internal processes within the system. These energy changes can be calculated using the first law of thermodynamics.

 

In thermodynamics, a system is a portion of the universe that we are interested in studying. It is the part of the world that we can observe and measure. A system can be as small as a single molecule or as large as the entire universe. We often think of a system as having boundaries that separate it from the surroundings.

The surroundings are everything outside of the system. They are the environment in which the system exists, and they can influence the behavior of the system. The surroundings can include other systems, objects, and the environment as a whole.

An open system is one that can exchange both matter and energy with its surroundings. In other words, an open system can transfer both mass and energy across its boundaries. An example of an open system is a pot of boiling water on a stove. The water can evaporate into the air, and energy in the form of heat can transfer to the stove and the surrounding air.

A closed system is one that can exchange energy but not matter with its surroundings. In other words, a closed system can transfer energy across its boundaries, but the mass of the system remains constant. An example of a closed system is a sealed container of gas. The gas can transfer heat energy to its surroundings, but the number of molecules inside the container remains constant.

In summary, in thermodynamics, a system is a part of the universe that we want to study, while surroundings are everything outside the system. Open systems can exchange both matter and energy with the surroundings, while closed systems can only exchange energy.

 

Enthalpy change is the amount of heat absorbed or released during a chemical reaction at constant pressure. The enthalpy change can be positive or negative, indicating whether the reaction is endothermic or exothermic, respectively. Here’s a detailed explanation of the enthalpy changes involved in the following processes:

1. Combustion: Combustion is a process in which a fuel reacts with oxygen to produce heat and light. The enthalpy change involved in combustion is the heat of combustion (ΔHc). It is the enthalpy change when one mole of a substance is completely burned in excess oxygen. The heat of combustion is always negative because it is an exothermic reaction. The enthalpy change is due to the breaking of the bonds in the fuel and the formation of new bonds in the products.
2. Atomization: Atomization is a process in which a substance is converted from a condensed phase to a gas phase, by breaking the intermolecular forces that hold the molecules together. The enthalpy change involved in atomization is the heat of atomization (ΔHat). It is the enthalpy change when one mole of a substance is converted into its gaseous atoms. The heat of atomization is always positive because it is an endothermic reaction. The enthalpy change is due to the energy required to break the bonds holding the molecules together.
3. Sublimation: Sublimation is a process in which a solid is converted directly into a gas without passing through the liquid phase. The enthalpy change involved in sublimation is the heat of sublimation (ΔHsub). It is the enthalpy change when one mole of a solid is converted into its gaseous phase. The heat of sublimation is always positive because it is an endothermic reaction. The enthalpy change is due to the energy required to break the intermolecular forces holding the molecules in the solid phase.
4. Hydration/salvation: Hydration is a process in which water molecules surround and interact with ions, while salvation is a similar process that occurs when a solute is dissolved in a solvent other than water. The enthalpy change involved in hydration/salvation is the heat of hydration/salvation (ΔHhydr/ΔHsol). It is the enthalpy change when one mole of ions or solute dissolves in water or other solvent. The heat of hydration/salvation can be positive or negative, depending on the nature of the solute and solvent. The enthalpy change is due to the breaking of the intermolecular forces between the solute and solvent and the formation of new solute-solvent bonds.
5. Dissolution: Dissolution is a process in which a solute dissolves in a solvent to form a homogeneous mixture. The enthalpy change involved in dissolution is the heat of solution (ΔHsoln). It is the enthalpy change when one mole of a solute dissolves in a solvent. The heat of solution can be positive or negative, depending on the nature of the solute and solvent. The enthalpy change is due to the breaking of the intermolecular forces between the solute and solvent and the formation of new solute-solvent bonds. If the heat of solution is negative, the solute is said to be exothermic and vice versa.