CHEMISTRY GLOSSARY

temperature    →   temperatura

Temperature is a measure to the average kinetic energy of its molecules. The SI unit in which thermodynamic temperature is expressed is the kelvin (K).

temperature rating    →   temperaturno područje

Temperature rating is the maximum and minimum temperature at which the material may be used in continuous operation without loss of its basic properties. For example, temperature ratings are often quoted for electrical insulators, specifying the maximum temperature at which they provide adequate protection against electrical breakdown.

transitional temperature    →   prijelazna temperatura

Transitional temperature is a temperature at which the crossing from one kind of crystals to another appears to be of the same matter (polymorphy).

logarithmic scale    →   logaritamska skala

Logarithmic scale is the one in which values of 1, 2, 3, 4, 5, in fact represents values of 1, 10, 100, 1 000, 10 000. Logarithmic scales are often used to simplify graphs and tables, where otherwise changes of data at the lower end of the scale would be difficult to distinguish (e.g. a graph axis which would normally have values from 1 - 1 000 000 is shown by values of 1 - 7). An example of a logarithmic scale is the pH scale.

Moh’s scale    →   Mohsova skala

Mohs’ scale of mineral hardness characterises the scratch resistance of various minerals through the ability of a harder material to scratch a softer. It was created by the German mineralogist Friedrich Mohs (1773-1839). Mohs based the scale on the ten readily available minerals.

degree    →   stupanj

1. Degree is a unit of temperature on a specified scale. The temperatures of boiling and freezing water are: in the Fahrenheit system 212 and 32 degrees; in the Celsius system 100 and 0 (zero) degrees.

2. Degree is a unit of angular measure. A circle is divided into 360 degrees, represented by the symbol °. Degrees are each divided into 60 minutes. Each minute has 60 seconds. Symbols for degree, minute, and second for plane angle is placed after the numerical value and a no space between the numerical value and the unit symbol (α = 2°3'4").

3. In algebra, the degree of a polynomial is the highest power of the variable in the polynomial. For example, 4x³ + 3x² + x + 7 have degree 3.

Charles’ law    →   Charlesov zakon

The volume of a fixed mass of gas at a constant pressure expand by the constant fraction of its volume at 0 °C. For each Celsius or kelvin degree its temperature is raised. For any ideal gas fraction it is approximately 1/273. This can be expressed by the equation

were V° is the volume at 0°C and V is its volume at t°C.

This is equivalent to the statement that the volume of a fixed mass of gas at a constant pressure is proportional to its thermodynamic temperature

This law also know as Gay-Lussac’s law.

An equation similar to the one given above applies to pressures for ideal gases:

cryogenic fractionation    →   kriogena frakcinacija

Cryogenic fractionation is a process of separation of gases by cooling them until they enter their liquid state. Large scale gas production companies use this method to produce liquid oxygen, liquid nitrogen etc. Gases have different boiling points (the temperature at which they change from liquid to gas). Oxygen has a boiling point of -183 °C, and nitrogen a boiling point of -195.8 °C. Therefore by cooling the gas mixture to -183 °C, the oxygen can be collected as liquid and the nitrogen remains its gaseous form.

specific heat    →   specifični toplinski kapacitet

Specific heat is the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius.

fuel cell    →   gorivi članak

Fuel cell is a device that converts chemical energy into electrical energy. It is different from a battery in that the energy conversion continues as long as fuel and oxidising agent are fed to the fuel cell; that is, in principle indefinitely. (A battery is manufactured with a limited amount of chemicals, and it is exhausted when all the chemicals have reacted.) It is a galvanic cell where spontaneous chemical reactions occur at the electrodes. The fuel is oxidised at the anode, and the oxidising agent (almost always oxygen or air) is reduced at the cathode. Presently, the most commonly used fuel is hydrogen. More conventional fuels (e.g., petrol or natural gas) must be converted (reformed) into hydrogen before they can be utilised in a fuel cell.

Some fuel cells employ an aqueous solution as electrolyte, that can be either acidic or basic (alkaline), or an ion-exchange membrane soaked in aqueous solution can act as the electrolyte. These fuel cells operate at relatively low temperatures (from room temperature to not much above the boiling point of water). Some fuel cells employ molten salts (especially carbonates) as electrolytes and have to operate at temperatures of several hundred degrees centigrade (Celsius). Others employ ionically conductive solids as electrolyte and must operate close to 1 000 °C.