Question

Define each of the following terms: a. heat b. energy c. work d. system e. surroundings f. exothermic reaction g. endothermic reaction h. enthalpy of reaction i. kinetic energy j. potential energy

Short answer

Heat is energy transferred due to temperature difference, energy is the capacity to do work, work is the energy transfer due to displacement, a system is the study subject in thermodynamics, surroundings are all outside the system, an exothermic reaction releases heat, an endothermic reaction absorbs heat, the enthalpy of reaction is the heat change at constant pressure during a reaction, kinetic energy is the energy of motion, and potential energy is the stored energy due to position.

Step-by-step solution

Defining Heat

Heat can be defined as a form of energy that is transferred between systems or objects with different temperatures. The transfer occurs from the hotter object to the colder one, until thermal equilibrium is reached.

Defining Energy

Energy is the capacity to do work. It exists in various forms such as heat, kinetic energy, potential energy, electrical, chemical, and nuclear energy. Energy can be converted from one form to another, though the total energy remains constant.

Defining Work

Work is the process of energy transfer that occurs when an object is moved over a distance by an external force at least partially applied in the direction of the displacement.

Defining System

A system in thermodynamics refers to the part of the universe under study, distinguished by boundaries, real or imaginary, from the rest of the universe, known as the surroundings.

Defining Surroundings

Surroundings are everything outside the system, which can interact with the system thermodynamically, exchanging energy and matter.

Defining Exothermic Reaction

An exothermic reaction is a chemical reaction that releases heat to its surroundings, resulting in a net release of energy as the total energy of the products is less than that of the reactants.

Defining Endothermic Reaction

An endothermic reaction is a chemical reaction that absorbs heat from its surroundings, resulting in a net absorption of energy as the total energy of the products is more than that of the reactants.

Defining Enthalpy of Reaction

The enthalpy of reaction is the heat change that occurs during a chemical reaction at constant pressure. It is defined as the difference between the enthalpy of the products and the reactants.

Defining Kinetic Energy

Kinetic energy is the energy possessed by an object due to its motion. It depends on the mass of the object and the square of its velocity.

Defining Potential Energy

Potential energy is the stored energy in an object or system due to its position in a force field or its configuration. Common types include gravitational potential energy and elastic potential energy.

Key concepts

Heat Transfer

Understanding heat transfer is essential in thermodynamics, which is the movement of heat energy from a warmer object to a cooler one. This occurs until the two objects reach the same temperature, a state called thermal equilibrium. In our daily lives, we experience heat transfer when a warm cup of coffee cools down to room temperature or when we heat our hands near a fire.

There are three modes of heat transfer: conduction, where heat moves through a solid material; convection, which occurs in fluids where warmer parts move towards cooler areas; and radiation, where heat is transferred through electromagnetic waves. Students should remember that heat always flows from hot to cold, following the second law of thermodynamics.

Energy Conservation

The principle of energy conservation states that energy cannot be created or destroyed, only transformed. This fundamental concept helps us understand why the total energy of an isolated system remains constant regardless of the processes happening inside it. This principle also underpins the first law of thermodynamics, which is essentially the law of conservation of energy applied to thermal processes.

For instance, when riding a bicycle down a hill, gravitational potential energy is converted into kinetic energy. Understanding this helps students recognize the continuous interchange of energy forms, like in power plants or living organisms.

Work in Physics

In physics, work is a measure of energy transfer that occurs when a force moves an object. It's determined by three factors: the magnitude of the force, the distance the object is moved, and the angle between the force and the displacement. An easy way to remember this is by the formula: work done (\( W \)) equals force (\( F \)) times distance (\( d \)) times the cosine of the angle (\( \theta \)) between them, or \( W = F \times d \times \text{cos}(\theta) \).

No work is done if an object doesn’t move or if the force is perpendicular to the direction of movement. This is why carrying a heavy bag while walking at a constant speed on a flat surface doesn't increase the bag's energy—it doesn’t do work on the bag.

Chemical System

A chemical system refers to the specific chemicals or substances involved in a reaction or process, contained within a defined boundary. For students studying thermodynamics, it is critical to distinguish the system from the surroundings since the energy exchange between the two defines how the reaction proceeds.

For instance, in a closed chemical system such as a sealed flask, matter does not enter or leave, but energy can be exchanged. Understanding a chemical system's boundaries aids in predicting behavioral changes under varying conditions like temperature or pressure.

Thermodynamic Surroundings

The thermodynamic surroundings include everything outside the boundaries of the studied system. They can absorb or supply heat and work to or from the system. For example, when you boil water in a pot, the stove supplies heat (surroundings) to the water (system).

Distinguishing the surroundings from the system helps in the study of energy exchanges. These surroundings can be anything from a laboratory bench to the entire universe, depending on the context of the thermodynamic analysis.

Exothermic Reaction

An exothermic reaction is chemically energetic, releasing heat into the surroundings and often feeling hot to the touch. Common examples include combustion in a fire or hand warmers that generate heat.

These reactions occur when the bonds formed in the product molecules need less energy to stabilize than the bonds that were broken in the reactants. This excess energy is then released as heat, which is why an exothermic reaction can be spontaneous and thermodynamically favorable.

Endothermic Reaction

On the flip side, an endothermic reaction absorbs heat from the surroundings, causing a drop in temperature around the reaction site. Photosynthesis in plants is an example, as plants absorb sunlight to convert carbon dioxide and water into glucose and oxygen.

In such reactions, more energy is needed to break the bonds of the reactants than is released when the new bonds in the products are formed. For these non-spontaneous reactions to continue, an external source of energy, such as heat or light, is often required.

Enthalpy

Enthalpy is a thermodynamic quantity representing the total heat content of a system, symbolized as (\( H \)). It's used in the calculation of the heat of reaction, or the enthalpy change (\( \text{∆}H \)), which shows whether a reaction is exothermic or endothermic. The equation (\( \text{∆}H = H_{products} - H_{reactants} \)) helps predict how much heat is released or absorbed during a reaction.

Remember, a negative (\( \text{∆}H \)) means an exothermic reaction, and a positive (\( \text{∆}H \)) signifies an endothermic reaction. Enthalpy relates closely to energy conservation, as it reflects the internal energy changes and external work done.

Kinetic Energy

Kinetic energy is the energy of motion. Any object that moves has kinetic energy, which increases with the object's mass and the square of its velocity (\( KE = \frac{1}{2}mv^2 \)), where (\( m \)) is mass and (\( v \)) is velocity. It's the energy associated with macroscopic motion, like a rolling ball, flowing water, or even the molecules moving in gases.

Understanding kinetic energy is important when studying energy conservation, as it's one of the forms energy can take and can be transformed into other types like potential energy.

Potential Energy

Potential energy is the stored energy in an object or system due to its position or configuration. It is relative to the object's arrangement with respect to the forces acting upon it. The most familiar form is gravitational potential energy (\( PE = mgh \)), where (\( m \)) is mass, (\( g \)) is the acceleration due to gravity, and (\( h \)) is height above a reference point.

In chemical systems, potential energy can also be thought of as the energy stored within the bonds between atoms. As these bonds are broken and formed during chemical reactions, the potential energy changes, contributing to the system's overall energy changes.