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Heat and Temperature

In order to understand about heat and temperature, it is of great importance to introduce the meaning of matter as well as the Kinetic Theory of Matter. This is because heat can be seen to exist when its effects are observed on matter. Without matter heat and temperature could not be realized. Matter can be defined as anything that has mass and that can occupy space. Matter is composed of substances, and these can be seen being made up of atoms, ions and molecules. Atoms, ions and molecules are the building blocks of matter; such that the behaviors of different types of substances are determined by these primary particles. The atoms of substances contain minute particles which are referred to as protons and electrons. These subatomic particles are also considered matter since they both have weight and occupy space (Atkins & Paula, 2002). 

Matter exists in three distinct states namely, solid state, liquid state and gaseous state. The three state of matter are inter-convertible such that one state can be converted into another state by changing the immediate environmental conditions especially temperature. The solid state of matter is characterized by having its own volume as well having a definite shape. Liquid state of matter is characterized by having its own volume but assumes the shape of the container it occupies. Gaseous state of matter does not have both its own volume and shape but occupies entire volume of the container and as well assumes the shape of the container it occupies (Atkins & Paula, 2002).

Kinetic Theory of Matter states that matter is made up of very many minute particles that are in a constant state of motion. The theory can also be referred to as the Kinetic Molecular Theory of Matter.  The theory forms the basis to explain the behavior that different forms of matter exhibit simply by making simple assumptions, for example, the idea that matter is composed of widely spaced particles which are in a constant motion. The significant areas in this case are transfer or flow of heat as well as the relationship between temperature, pressure, and volume of gases. The Kinetic Theory of matter is a mere prediction regarding the behavior of matter, based on particular approximations and assumptions. These assumptions and approximations are made from experiments and observations, for instance, the fact that objects are made up of atoms or small molecules (Burshtein, 1996). 

Heat can be defined as a form of energy that is associated with the motion of molecules or atoms and that can be conveyed through fluid and solid media by the process of conduction, through vacuum by the process of radiation, and through fluid media by convection process.  There are different sources of heat, for instance, heat due to friction, heat due to nuclear reactions, heat due to sun, heat due to burning of fossil fuels, and heat due to electricity. This transmission of energy from one substance to another is determined by a change in phase or a difference in temperature. Therefore temperature can be defined as the measure of the mean kinetic energy of the molecules or atoms in a given sample of matter, and it is usually expressed in degrees or units chosen on a typical scale. The relationship between heat and temperature is depicted from the definitions. Temperatures of substances rise when heat is supplied. Intense heat is characterized by high temperature (Turns, 2006).

Now it will be very clear, if in the discussion of converting substances from one state to another immediate state, heat and temperature are involved. From the Kinetic Theory of Matter, it is evident that matter is made up of small particles that are in a constant state of motion. These particles may consist of molecules, ions or atoms which are held together by strong forces of attraction. In the solid state, the particles are closely packed together in fixed positions. The particles cannot move from one position to another but can vigorously vibrate within their fixed positions, and this is because the forces of attraction between the particles are very strong. With the increase in the temperature of a substance in solid state, the particles gain heat energy gradually and the kinetic energy of the particles increases. A point is reached when the particles start to move more vigorous until the forces of attraction between them weakens.  The particles can now move from one place to another as the substance changes state from solid to liquid. The substance loses its definite shape but it still has its own volume (Atkins & Paula, 2002).

In the liquid state, the particles are not as closely held together as in the solid states since the forces of attraction between the particles are a bit weaker. The particles are free to move from one place to another within the structure. When the temperature of the substance is increased further, the particles gradually absorb heat energy. The kinetic energy of the particles further increases as the particles move more vigorous. A point reaches when the forces of attraction between the particles are overcome and the particles move far apart from one another. At this point the substance changes its state from liquid to gaseous state (Turns, 2006). 

Reduction in temperature reverses the processes, such that the substance in gaseous state changes into liquid state and finally into solid state. This is because, as the temperature reduces, the kinetic energy of the particles goes down and the forces of attraction become stronger. Thus the particles of the substance attract one another.

Heat capacity of a substance is defined as a measurable physical quantity that portrays the amount of heat needed to change the temperature of a body by a particular amount. The SI units for heat capacity are joules per Kelvin. In substances heat capacity is determined by various properties for example the amount of matter in the substance expressed in terms of its mass, the type of material of which the substance is composed of, the temperature of the substance, and the atmospheric pressure (White, 1999).        


Atkins, P., & Paula, J. (2002). Atkins' Physical Chemistry. Oxford Oxfordshire: Oxford University Press.

Burshtein, a., (1996). Introduction to Thermodynamics and Kinetic Theory of Matter.  London: J. Wiley.

Turns, S., (2006). Thermal-Fluid Sciences. Cambridge: Cambridge University Press.

White, G., (1999). Heat Capacity and Thermal Expansion at Low Temperatures. New York:  Kluwer Academic/Plenum.

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