CHEMISTRY GLOSSARY

catalyst    →   katalizator

Catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Catalysts that have the same phase as the reactants are homogenous catalysts (e.g. enzymes in biochemical reactions). Those that have a different phase are heterogeneous catalyst (e.g. metals or oxides used in gas reactions).

The catalyst provides an alternative pathway by which the reaction can proceed, in which the activation energy is lower. In thus increases the rate at which the reaction comes to an equilibrium, although it does not alter the position of the equilibrium.

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:

Grignard reagent    →   Grignardov reagens

Grignard reagents are organomagnesium halides, RMgX, having a carbon- magnesium bond (or their equilibrium mixtures in solution with R₂Mg + MgX₂).

harmonic motion    →   harmoničko gibanje

Harmonic motion is caused by restoring force, acting on a body that is displaced from its equilibrium position. This force tries to put the body back in equilibrium. Usual examples are the motion of a body attached to elastic spring (see: Hooke’s law) and the motion of mathematical pendulum. The body undergoes periodic motion around the equilibrium point.

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.

chemical reaction equation    →   jednadžba kemijske reakcije

Chemical reactions are symbolically shown with chemical equations. On the left side of the equation we write formulas or substance symbols which enter the chemical reaction, reactants. On the right side formulas or substance symbols which emerge from the chemical reaction, products, are writen.

Each chemical reaction leads to an equilibrium which is moved more or less to one side (left or right). Because of that, in reversible reactions instead of = sign two opposite arrows are put

In order to write down certain chemical reaction equation all reactants and all products and their stechiometric proportions must be known. (See Chemical reaction balancing)

chlorinity    →   klorinitet

Originally chlorinity (symbol Cl) was defined as the weight of chlorine in grams per kilogram of seawater after the bromides and iodides had been replaced by chlorides. To make the definition independent of atomic weights, chlorinity is now defined as 0.3285233 times the weight of silver equivalent to all the halides.

The Mohr-Knudsen titration method served oceanographers for more than 60 years to determine salinity from chlorinity. This modification of the Mohr method uses special volumetric glassware calibrated directly in chlorinity units. The Mohr method uses potassium chromate (K₂CrO₄) as an indicator in the titration of chloride ions chloride (plus a small amount of bromide and iodide) with a silver nitrate (AgNO₃) standard solution.

The other halides present are similarly precipitated.

A problem in the Mohr titration was that silver nitrate is not well suited for a primary standard. The Danish physicist Martin Knudsen (1871-1949) suggested that a standard seawater (Eau de mer Normale or Copenhagen Normal Water) be created and distributed to oceanographic laboratories throughout the world. This water was then used to standardize the silver nitrate solutions. In this way all chlorinity determinations were referred to one and the same standard which gave great internal consistency.

The relationship between chlorinity Cl and salinity S as set forth in Knudsen's tables is

In 1962, however, a better expression for the relationship between total dissolved salts and chlorinity was found to be

isochore    →   izohora

Isochore is a line or surface of constant volume on a graphic representation of a physical system.

latent heat    →   latentna toplina

Latent heat (L) is the quantity of heat absorbed or released when a substance changes its physical phase at constant temperature (e.g. from solid to liquid at the melting point or from liquid to gas at the boiling point).

Clapeyron equation    →   Clapeyronova jednadžba

Clapeyron equation (also called the Clausius-Clapeyron equation) is a relation between pressure and temperature of two phases of a pure substance that are in equilibrium,

where Δ_trsS is the difference in entropy between the phases and Δ_trsV the corresponding difference in volume.