أكاديميا - كولنز - معاجم الجيب العلمية - الكيمياء - انكليزي - فرنسي - عربي الحرف ٣_ e

Academia - Collins - Pocket Scientific Dictionaries - Chemistry - English - French - Arabic Letter 3_ E


end point
Point m to view

End point. The point at which the reaction takes place and is completed. The end point of titration is when all of the reactants are consumed. The end point can be determined by an indicator or by a device or tool such as a pH meter or a conductivity meter. Thus, the end point is when the color of the indicator changes.


energy
energy f

)) energy. The ability to do useful work. Energy is trapped in the nuclei of atoms and can sometimes be released (see nuclear reactions). Energy is also found in bonds between atoms. When chemicals interact, bonds break and new ones are formed in their place. During this disintegration and formation, energy can be absorbed or released, such as thermal energy (see energy change). In batteries, the energy is released in the form of electrical energy. Energy is usually measured in joules or kilojoules. See enthalpy.


energy change
Energy reaction

Energy change. When chemical reactions occur, the reactants can release thermal energy, and the release of thermal energy by the reactants is called an exothermic reaction. If the reactants receive thermal energy, it is called an endothermic reaction.
Energy changes are measured in joules or kilojoules and refer to a specific amount of a substance, usually one mole. Thus, the energy change in the Haber process is - 92 kilojoules per mole.


enthalpy(H)
enthalpie f

Enthalpy The amount of heat energy in a chemical substance. It is indicated by the symbol... and the amount of this energy cannot be measured. When chemicals interact, the difference in thermal energy between the reactants and the resulting materials can be measured using a thermometer.
This difference is the enthalpy change and is indicated by the symbol AH. This symbol is negative in an exothermic reaction and positive in an endothermic reaction.

enzyme
enzyme m

Enzyme. Enzymes are usually protein molecules. They are catalysts found in living tissues that allow complex chemical reactions to occur at low temperatures and pressures inside the body. It is believed that the enzyme has a specific shape, and this shape allows two interacting molecules to come close to meeting on the enzyme. This facilitates the interaction, for example:

Maltose <--- Epitalin ----- Starch
Two reacting substances
Enzyme
The resulting
Interaction


equation
equation f

Equation In chemistry, a reaction can be described by an equation. The equation can be a “words” equation,
like :

Water > oxygen + hydrogen

Or it can be an equation of formulas” (or “symbols”), such as:

H2 + O2→ H2O

The equation is balanced if there is a
The equation is the same number of each type of atom, for example:

2H2+O2→ 2H2O

It is a balanced equation.

A hydrogen molecule reacts with an oxygen molecule to produce two water molecules. The equation also tells us that 2 moles, or 4 grams, of hydrogen react with 1 mole, or 32 grams, of oxygen to produce 2 moles, or 36 grams, of water. Given that the relative atomic masses of the two are: H = 1 and O = 16, then:

2H2+O2→ 2H2O

2(2) + 32 → 2(1+16) = 36

Ionic equations are sometimes used, such as:

Cu2+ + Zn → Cu + Zn2+

State symbols are usually added after
The formula to indicate the state of matter. For example, hydrogen and oxygen gases react to produce liquid water:

2H2 (gas) + O2 (gas) → 2H2O (liquid)

balance
equilibre m

Equilibrium in a reversible reaction The reaction can go in both directions, for example:
3Fe + 4H2O = FeO + 4H2

(gas) (solid) (gas) (solid)

The reactants produce iron, steam, oxide and hydrogen. Once the two products are made, they begin to react to reform steam and iron. There may eventually come a time when the rate of the forward reaction equals the rate of the reverse reaction. At this point, the percentage of materials present is constant. It seems as if there is no interaction. There is a balance between the forward and reverse reactions. It is important to know that such an equilibrium is a dynamic equilibrium. Both reactions are taking place, but because they are taking place at the same rate, nothing can be seen.

There are many important interactions with equilibrium. In the Haber process, under normal working conditions, less than 20 percent of hydrogen and nitrogen are converted to ammonia. This is the equilibrium yield of ammonia in the reaction.