Heat is one of the most fundamental concepts in physics. The goal of this paper is to highlight the most important aspects in the study of heat physics. The paper describes the way in which the study of heat relates to the kinetic theory of matter. Definitions of heat and temperature are provided. The complex relationship between heat and temperature is described. The concept of heat capacity, the properties of a substance determining heat capacity, and various sources of heat are described.
Keywords: heat, kinetic, energy, heat substance, temperature, substance, matter.
Heat is a fundamental concept in the study of matter (Sullivan & Edmondson, 2008). For many years, heat had been one of the most enigmatic properties of substances. It was not until the middle of the 19th century that heat was recognized as a form of energy that could be converted into a different form (Cassidy, Holton, Rutherford, & Rutherford, 2002). As of today, heat is an indispensable element of the kinetic theory of matter. Heat has come to represent a specific type of molecular and atomic motion, while heat capacity represents a vital physical property of any substance. Heat is intricately related to temperature, while the heat capacity of substances is determined by their molecular/atomic structure, composition, temperature, and physical pressure.
Heat: The Kinetic Theory of Matter
Cassidy et al. (2002) write that “heat is a matter of motion” (p.293). This is one of the easiest ways to describe how and why heat relates to the kinetic theory of matter. As mentioned earlier, in the middle of the 19th century, scientists finally recognized that heat was a special form of energy that could be converted into a different form (Cassidy et al., 2002). With time, scientists discovered that heat could transform into mechanical energy, and vice versa (Cassidy et al., 2002). Consequently, researchers concluded that heat was the kinetic energy of atoms and molecules making up the substance (Cassidy et al., 2002). This assumption is actually the foundational pillar of the kinetic theory of matter. Unfortunately, in the 19th century, scientists did not have any technological capacity to observe molecules and atoms. Therefore, they could not confirm that what they called “heat” was actually the kinetic energy of molecules (Cassidy et al., 2002). They chose the easiest way to check their hypotheses and used gases to test their kinetic properties (Cassidy et al., 2002). The kinetic theory of gases was developed in the 19th century and created the foundation for the development of the kinetic theory of matter and advanced thermodynamics. As of today, “the basic idea of the kinetic theory of matter is that heat energy is related to the kinetic energy of moving molecules” (Cassidy et al., 2002, p.302). This is how heat is related to the kinetic theory of matter.
Heat and Temperature: A Complex Relationship
One of the most interesting in the study of matter is the relationship between heat and temperature. Very often, the terms “heat” and “temperature” are used interchangeably. Yet, in reality, these terms have different meanings and describe different concepts. The relationship between heat and temperature remains one of the central to the study of matter and its physical properties. Heat is the way energy is transferred between the substance and its surroundings (Myers, 2006). More specifically, heat can be defined as the act of thermal energy transfer from a high-temperature body to a body with lower temperature (Myers, 2006). Heat is sometimes used as a synonym to energy, but not all energy is heat. Heat is limited to thermal energy and involves the transfer of thermal energy only (Myers, 2006). All substances and systems always possess a certain amount of energy, but not heat (Myers, 2006). Heat comes into play only when the act of thermal energy transfer takes place (Myers, 2006).
Heat and temperature are closely related, but defining the concept of temperature is not easy. Temperature is one of those terms which are regularly used in science and daily life but are rarely given any professional consideration (Myers, 2006). There is hardly any person in the developed world, who has never measured temperature, either body temperature or the temperature of the environment/atmosphere. Temperature is associated with the changes in heat levels, and non-physicists interpret this measure in terms of cold and hot (Myers, 2006). In reality, “temperature is a measure of the random motion of the particles (atoms, molecules, ions) making up a substance” (Myers, 2006, p.71). Temperature measures the kinetic energy of particles within a substance (Myers, 2006). Temperature is not the same as heat, although both concepts are intricately related. While heat represents the transfer of thermal energy from one substance to another, temperature is just a measure of changes in the kinetic energy of motion among these substances.
Changes in weather best illustrate the difference between heat and temperature. The atmosphere is made of oxygen and nitrogen molecules (Myers, 2006). All these molecules possess a certain amount of kinetic energy (Myers, 2006). They move at different speeds: some move slower, while others move faster. The graph below shows the way these speeds are distributed.
The way this graph is shaped depends directly upon temperature: the higher the temperature, the faster the molecules are moving (Myers, 2006). At higher velocities, the kinetic energy of atmospheric molecules is also high, while lower velocities presuppose slower movements and lower kinetic energy of the particles (Myers, 2006). As a result, any change in temperature is a measurable reflection of the change in the kinetic energy of atmospheric molecules. At higher temperatures, thermometers are subject to faster and more frequent collisions with atmospheric molecules, which also have higher kinetic energy (Myers, 2006). Under lower temperatures, the situation is quite the opposite. Under the influence of these collisions and kinetic energies, the mercury contained in the thermometer either expands or shrinks, causing the thermometer to register a higher or lower temperature, accordingly (Myers, 2006). As of today, the two most popular scales to measure temperature are the Celsius and Fahrenheit scales (Myers, 2006). In the scientific circles, the Kelvin temperature scale is also used. It is the most popular absolute temperature scale (Myers, 2006).
Heat Capacity and Properties of a Substance
When discussing the relationship between heat and temperature, special attention needs to be paid to the concept of heat capacity. Heat capacity is usually defined as the amount of energy needed to raise the temperature by 1 Kelvin. Specific heat capacity is the amount of energy needed to raise the temperature of 1 mass unit of the substance by 1 Kelvin (Myers, 2006). Heat capacity is one of the definitive physical properties of a substance, and different substances display different heat capacities. For example, water is well-known for its particularly high heat capacity, whereas most metals possess extraordinarily low specific heats. The heat capacity of a substance usually depends on its properties, including composition, pressure, and temperature.
Speaking about composition, the unusually high heat capacity of water is explained by the presence of the so-called hydrogen bonding. The latter is a unique intermolecular force that keeps water molecules together (Burton, 2000). Hydrogen bonding is a force much stronger than any other intermolecular forces. As a result, one needs considerable amounts of energy to raise the temperature of water by at least 1 degree. The heat capacity of any substance, including water, may also change as a result of shifts in energy distribution. Depending on the composition of the substance, its molecules will have different sizes and electrical charges. The latter, in turn, predetermine the power and stability of the intermolecular forces and the amount of energy needed to break these ties.
The main sources of heat include electricity, nuclear reactions, and simple friction. Electricity causes movements and energy increases in wire particles, while the energy released by the Sun is the brightest example of the way nuclear reactions produce heat. The simplest and most demonstrative is, probably, the example of friction: it is just enough to have one’s hands rubbed and placed against one’s face, to feel the change in heat and temperature. Despite the abundant information, scientists still lack a complete picture of heat and temperature. Physics constantly evolves, and new technologies will enable physicists to look deeper into the most important properties of a substance.
Heat is the fundamental concept in the study of matter. Heat is the central element of the kinetic theory of matter. Heat is the motion; it is the kinetic energy of molecules. This is why the concept of heat is inseparable from the scientific study of the properties of a substance. Heat is directly related to temperature, but the difference between these two concepts should not be ignored. Despite the abundant information, only new technologies will enable physicists to look deeper into the most important properties of a substance.