CHEMISTRY GLOSSARY

collision theory    →   teorija sudara

Collision theory is theory that explains how chemical reactions take place and why rates of reaction alter. For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change; these are called successful collisions. The successful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants and raising the temperature bring about more collisions and therefore more successful collisions, increasing the rate of reaction.

inert electrode    →   inertna elektroda

Inert electrode is an electrode that serves only as a source or sink for electrons without playing a chemical role in the electrode reaction. Precious metals, mercury, and carbon are typically used as inert electrodes. The inert nature of the electrode can sometimes be questioned. While the electrode may not take part in the reaction as a reactant or product, it still can act as an electrocatalyst.

precursor    →   prekursor

Precursor means any chemical reactant which takes part at any stage in the production by whatever method of a toxic chemical. This includes any key component of a binary or multicomponent chemical system. A zymogen (or proenzyme) is an inactive enzyme precursor.

product    →   produkt

Products are substances developed by chemical reactions from reactants.

reaction speed curve    →   krivulja brzine reakcije

Reaction speed curve is a graphic presentation of the reactant quantity change in dependence on time value.

reverse reaction    →   povratna reakcija

Reverse reaction is a reaction in backward directions, reaction (in the reversible reaction) in which original reactants emerge again from a products. It goes from right to left.

equilibrium constant    →   konstanta ravnoteže

The equilibrium constant (K) was originally introduced in 1863 by Norwegian chemists C.M. Guldberg and P. Waage using the law of mass action. For a reversible chemical reaction represented by the equation

chemical equilibrium occurs when the rate of the forward reaction equals the rate of the back reaction, so that the concentrations of products and reactants reach steady-state values.

The equilibrium constant is the ratio of chemical activities of the species A, B, C, and D at equilibrium.

To a certain approximation, the activities can be replaced by concentrations.

For gas reactions, partial pressures are used rather than concentrations

The units of K_p and K_c depend on the numbers of molecules appearing in the stoichiometric equation (a, b, c, and d).

The value equilibrium constant depends on the temperature. If the forward reaction is exothermic, the equilibrium constant decreases as the temperature rises. The equilibrium constant shows the position of equilibrium. A low value of K indicates that [C] and [D] are small compared to [A] and [B]; i.e. that the back reaction predominates.

The equilibrium constant is related to Δ_rG°, the standard Gibbs free energy change in the reaction, by

synthesis    →   sinteza

Synthesis is a formation of a complex product from simpler reactants. For example, water can be synthesised from oxygen and hydrogen gas:

zero-order reaction    →   reakcija nultog reda

Zero-order reaction is a reaction for which the rate of reaction is independent of the concentration of reactants.

reversible reaction    →   reverzibilna reakcija

Reversible reaction is a chemical reaction that can proceed in both the forward and backward directions. When reversible reactions reach equilibrium the forward and reverse reactions are still happening but at the same rate, so the concentrations of reactants and products do not change. A reversible reaction is denoted by a double arrow pointing both directions in a chemical equation.