CHEMISTRY GLOSSARY

heat of crystallization    →   toplina kristalizacije

Heat of crystallization or enthalpy of crystallization is the heat evolved or absorbed when one mole of given substance crystallises from a saturated solution of the same substance.

heat of formation    →   toplina nastajanja

Heat of formation or enthalpy of is formation the heat evolved or absorbed when one mole of a compound is formed in its standard state from its constituent elements.

heat capacity    →   toplinski kapacitet

Heat capacity is defined in general as dQ/dT, where dQ is the amount of heat that must be added to a system to increase its temperature by a small amount dT. The heat capacity at a constant pressure is C_p = (∂H/∂T)_p; that at a constant volume is C_V = (∂E/∂T)_V, where H is enthalpy, E is internal energy, p is pressure, V is volume, and T is temperature. An upper case C normally indicates the molar heat capacity, while a lower case c is used for the specific (per unit mass) heat capacity.

heat of hydration    →   toplina hidratacije

Heat of hydration or enthalpy of hydration of ions corresponds to the heat that is released by hydration of one mole of ions at a constant pressure. The more the ion is hydrated, the more heat is released. Degree of hydration depends on the size and charge of ion. The smaller the ion and the greater its charge, it will be the more hydrated.

heat of reaction    →   toplina kemijske reakcije

Heat of reaction or enthalpy of reaction is the heat evolved or absorbed as a result of the complete chemical reaction of molar amounts of the reactants.

heat of sublimation    →   toplina sublimacije

Heat of sublimation or enthalpy of sublimation is the energy required to convert one mole of a substance from the solid to the gas state (sublimation) without the appearance of the liquid state.

Henry’s law    →   Henryjev zakon

Henry’s law was discovered in 1801 by the British chemist William Henry (1775-1836). At a constant temperature the mass of gas dissolved in a liquid at equilibrium is proportional to the partial pressure of the gas. It applies only to gases that do not react with the solvent.

where p_i is the partial pressure of component i above the solution, x_i is its mole fraction in the solution, and K_x is the Henry’s law constant (a characteristic of the given gas and solvent, as well as the temperature).

law of chemical equilibrium    →   zakon o kemijskoj ravnoteži

Law of chemical equilibrium (also called the law of mass action) states that the rate at which a substance reacts is proportional to its active mass (i.e. to its molar concentration). Thus, the velocity of a chemical reaction is proportional to the product of the concentration of the reactants.

liquid crystal    →   tekući kristal

Liquid crystals or crystalline liquids are a physical state between crystals and melts. The liquid crystalline phase - the so-called mesophase - is formed at the melting point. The most important (usable) mesophases are nematic, cholesteric and smectic phase, having different molecular orientations.

Hesse’s law    →   Hessov zakon

Hesse’s law says that reaction heat of some chemical change does not depend on the way in which the reaction is conducted, but only on starting and ending system state. Hesse’s law is also known as the law of constant heat summation. Hesse’s law is also known as the law of constant heat summation. The law was first put forward in 1840 by the Swiss-born Russian chemist Germain Henri Hess (1802-1850).

Hesse’s law can be used to obtain thermodynamic data that cannot be measured directly. For example, it is very difficult to control the oxidation of graphite to give pure CO. However, enthalpy for the oxidation of graphite to CO₂ can easily be measured. So can the enthalpy of oxidation of CO to CO₂. The application of Hess’s law enables us to estimate the enthalpy of formation of CO.

The equation shows the standard enthalpy of formation of CO to be -110 kJ/mol.