Chapter 4: Heat and Temperature

The Kinetic Molecular Theory

• All matter is made up of tiny, basic units of structure called atoms. Atoms are made of extremely small particles called protons and electrons.

• Different configurations of electrons and protons produce unique elements with unique physical and chemical properties.

• A molecule is generally defined as tightly bound group of atoms.

• Molecules interact with other molecules. When we observe an attractive force between same kind of molecules, it is called cohesion. When the attractions between different kind of molecules we call it adhesion.

Phases of Matter

Matter can exist in three primary phases: solid, liquid, and gas. These phases are determined by the arrangement and behavior of the particles that make up the substance.

Solid

Particles are closely packed together in a regular, organized arrangement. They have strong intermolecular forces holding them in place, which results in a fixed shape and volume. Solids are characterized by their rigidity and resistance to changes in shape and volume. However, the particles still vibrate in their positions, and as temperature increases, the amplitude of this vibration also.

Liquid

Particles are still in close proximity to each other, but they have more freedom to move around compared to solids. The intermolecular forces in liquids are weaker than in solids, allowing the particles to flow and take the shape of the container they occupy. However, liquids still have a fixed volume due to the cohesive forces between particles. Liquids also have the ability to evaporate and change into the gas phase with sufficient energy.

Gas

Particles have significant energy and are far apart from each other, resulting in a lack of strong intermolecular forces. Gas particles move freely and randomly in all directions, colliding with each other and the walls of the container. Gases have neither a fixed shape nor a fixed volume, as they expand to fill the entire available space. The behavior of gases is described by various gas laws, such as Boyle's law and Charles's law.

Plasma

Ionized gas phase that occurs at very high temperatures or in the presence of strong electromagnetic fields. In plasma, some or all of the electrons are separated from their parent atoms, resulting in a mixture of free electrons and positively charged ions. Plasma is commonly observed in stars, lightning, and certain technological applications like fluorescent lights and plasma TVs.

Molecules Move

The relationship between the temperature of a gas and the motion of molecules shows that the average kinetic energy is proportional to the temperature. Hence the temperature of a
substance is a measure of the average kinetic energy of the molecules making up the substance.

Temperature

• Temperature is a measure of the average kinetic energy of atoms and molecules in an object.

• A thermometer is an instrument that measures temperature by comparing the expansion and contraction of a liquid as it gains or loses thermal
  energy.

• There are three temperature scales in use:
  • Fahrenheit scale
  • Celsius scale
  • Kelvin scale (used in scientific research)

Celsius (°C)

Also known as the Centigrade scale, is the most widely used temperature scale worldwide. It is based on the melting
and boiling points of water, with 0°C representing the freezing point and 100°C representing the boiling point of water at sea level.

Fahrenheit (°F)

Primarily used in the United States and a few other countries. It is also based on the freezing and boiling points of water, with 32°F representing the freezing point and 212°F representing the boiling point of water at sea level.

Kelvin (K)

Absolute temperature scale commonly used in scientific and engineering applications. It starts at absolute zero, the theoretical point at which all molecular motion ceases, which is approximately -273.15°C or -459.67°F. The Kelvin scale is used extensively in fields such as physics, chemistry, and thermodynamics.

Converting between different temperature scales…

The following equations can be used to convert between Celsius
scale to Fahrenheit and vis-versa.

The following equation can be used to convert between Celsius
scale to Kelvin scale and vis-versa.

Answer: 27

External Energy & Internal Energy

• External energy is the total potential and kinetic energy of an object. All energies we discussed in the previous chapters werereferring to external energy.

• Internal energy is the total kinetic and potential energy of the molecules of an object.

Heat as energy transfer

Heat refers to the transfer of energy between objects or systems due to a
temperature difference. It is a form of energy that flows from an object with
a higher temperature to an object with a lower temperature until thermal
equilibrium is reached.
Heat is based on the total internal energy of an object. Heat is measured in
units of energy—joules or calories.
A calorie is defined as the amount of heat needed to raise the temperature
of 1 gram of water by 1 Celsius degree.
4.19 joules = 1 calorie

Specific Heat

Each substance has its own specific heat, which is defined as
the amount of energy (or heat) needed to increase the
temperature of 1 gram of a substance 1 degree Celsius.

Heat Flow

• Conduction: The transfer of heat from a region of higher temperature to a region of lower temperature by increased kinetic energy moving from molecule to molecule. Hotter atoms collide with cooler ones, transferring some of their energy.
• Direct physical contact required; cannot occur in a vacuum.

Sample Conductivities

• Good Conductors: Copper, Gold, Aluminum, Silver
• Poor conductors = insulators (Styrofoam, wool, air...)

Convection

Transfer of heat from a region of higher temperature to a region of lower temperature by the displacement of high-energy molecules; for example, the displacement of warmer, less dense air (higher kinetic energy) by cooler, more dense air (lower kinetic energy).

Radiation

The transfer of heat from a region of higher
temperature to a region of lower temperature by greater
emission of radiant energy from the region of higher
temperature. It is the energy associated with electromagnetic.

Temperature determines
• Emission rate
• Intensity of emitted light
• Type of radiation given off

Phase Change

•Phase change refers to the action of a substance changing
from one state of matter to another. A phase change always
absorbs or releases internal potential energy without a
temperature change.
Matter can response in two ways when heat is provided:
•Temperature can increase within a given phase (solid, liquid,
gas)
•Phase change at constant temperature (e.g. liquid to gas)

Latent Heat of Fusion

The heats absorbed when 1 gram of a substance changes from the solid to the liquid phase, or the heat released by 1 gram of a substance when changing from the liquid phase to the solid phase. This is the heat involved in the breaking or making of bonds in a solid-liquid phase changes.

Latent Heat of Vaporization

The heat absorbed when 1 gram of a substance changes from the liquid phase to the gaseous phase, or the heat released when 1 gram of gas changes from the gaseous phase to the liquid phase. This is the heat involved in a liquid-gas phase change where there is an evaporation or condensation.

Evaporation

Liquids do not have to be at the boiling point to change to a gas and in fact they can undergo a phase change at any point. If a liquid molecule near the surface has enough energy to overcome the attractive forces of the other molecules, it can escape the liquid and can become a gas.

Condensation

Condensation is the change of the state of matter from the gas phase into the liquid phase and is the reverse of vaporization. In condensation more molecules are returning to the liquid state than are leaving. Gas molecules near the surface lose KE to liquid molecules and merge.

Zeroth Law of Thermodynamics

It is considered foundational and essential for defining temperature and thermal equilibrium. It states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This law allows for the
establishment of a temperature scale and is the basis for
temperature measurement.

First Law of Thermodynamics

Law of Energy Conservation: This law states that energy cannot be created or destroyed in an isolated system. It can only be transferred or converted from one form to another. The total energy of a closed system remains constant, and any energy input into the system is either used to do work or increase the internal energy of the system.

Second Law of Thermodynamics

Introduces the concept of entropy, which is a measure of the disorder or randomness in a system. It states that the total entropy of an isolated system always increases over time or remains constant in reversible processes. This implies that the total entropy of the universe continually increases.

In other words, natural processes tend to move towards a
state of greater disorder. This law also implies the existence of
a direction for heat flow, from higher temperature regions to
lower temperature regions.

Third Law of Thermodynamics

Deals with the behavior of systems as they approach absolute zero temperature. It states that as the temperature of a system
approaches absolute zero (0 Kelvin or -273.15 degrees
Celsius), the entropy of the system approaches a minimum
value. This law provides insights into the behavior of matter at
extremely low temperatures.