FHSST Physics/Heat and Properties of Matter/Thermal Properties

= Thermal Properties of Materials = R

Specific heat capacity

Conversion of macroscopic energy to microscopic kinetic energy thus tends to raise the temperature, while the reverse conversion lowers it. It is easy to show experimentally that the amount of heating needed to change the temperature of a body by some amount is proportional to the amount of matter in the body. Thus, it is natural to write

$\Delta Q=MC\Delta T$

(23.4)

Riaan Note: not sure about the equation numbers, sticking to those in the PDF released the 1st of March 2005

where $M$ is the mass of material, $\Delta Q$ is the amount of energy transferred to the material, and $\Delta T$ is the change of the material's temperature. The quantity $C$ is called the specific heat of the material in question and is the amount of energy needed to raise the temperature of a unit mass of material one degree in temperature. $C$ varies with the type of material. Values for common materials are given in table 22.2.

Table 22.2: Specific heats of common materials. Material C ($Jkg^{-1}K^{-1}$) brass 385 glass 669 ice 2092 steel 448 methyl alcohol 2510 glycerine 2427 water 4184

Specific latent heat

When a material changes phases from solid to liquid, or from liquid to gas, a certain amount of energy is involved in this change of space.

First law of thermodynamics

We now address some questions of terminology. The use of the terms heat and quantity of heat to indicate the amount of microscopic kinetic energy inhabiting a body has long been out of favor due to their association with the discredited caloric theory of heat. Instead, we use the term internal energy to describe the amount of microscopic energy in a body. The word heat is most correctly used only as a verb, e. g., to heat the house . Heat thus represents the transfer of internal energy from one body to another or conversion of some other form of energy to internal energy. Taking into account these definitions, we can express the idea of energy conservation in some material body by the equation

$\Delta E=\Delta Q-\Delta W$

(first law of thermodynamics)

where $\Delta E$ is the change in internal energy resulting from the addition of heat $\Delta Q$ to the body and the work $\Delta W$ done by the body on the outside world. This equation expresses the first law of thermodynamics. Note that the sign conventions are inconsistent as to the direction of energy flow. However, these conventions result from thinking about heat engines, i. e., machines which take in heat and put out macroscopic work. Examples of heat engines are steam engines, coal and nuclear power plants, the engine in your automobile, and the engines on jet aircraft.