Unit 3 chemistry

I. Read and translate

The reaction of two or more elements together results in the formation of a chemical bond between atoms and the formation of a chemical compound. All chemical reactions are accompanied by a change in energy. Some reactions release energy to their surroundings (usually in the form of heat) and are called exothermic. On the other hand, some reactions need to absorb heat from their surroundings to proceed. These reactions are called endothermic.

Oxidation, reduction, dissociation, acid-base neutralization and molecular rearrangement are some of the commonly used kinds of chemical reactions.

A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. An example of this kind of reaction is the burning of naphthalene:

C₁₀H₈ + 12O₂ ---> 10CO₂ + 4H₂O

A synthesis reaction is when two or more simple compounds combine to form a more complicated one. One example of a synthesis reaction is the combination of iron and sulfur to form iron (II) sulfide:

8Fe + S₈ ---> 8FeS

A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas:

2H₂O ---> 2H₂ + O₂

Single displacement: This is when one element trades places with another element in a compound. One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:

Mg + 2H₂O ---> Mg(OH)₂ + H₂

Double displacement: This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:

Pb(NO₃)₂ + 2KI ---> PbI₂ + 2KNO₃

Acid-base: This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide:

HBr + NaOH ---> NaBr + H₂O

II. Read and translate the international words

reaction, composition, structure, atom, atomic, molecule, molecular, geology, biology, tradition, traditional, elementary, metal, metallic, crystal, aggregate, isolation, combination, transformation, laboratory, preparation, organic, component, quantum, organometallic, discipline

to study, to focus on, to deal with, to consist of, to be concerned with, to connect with, to distinct from, to start with, to involve, to take place.

III. Read and translate

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds. Chemistry is sometimes called ‘the central science’ because it connects physics with other natural sciences such as geology and biology. Chemistry is a branch of physical science but distinct from physics.

Traditional chemistry starts with the study of elementary particles, atoms, molecules, substances, metals, crystals and other aggregates of matter in solid, liquid, and gas states, whether in isolation or combination. The interactions, reactions and transformations that are studied in chemistry are a result of interaction either between different chemical substances or between matter and energy. Such behaviors are studied in a chemistry laboratory using various forms of laboratory glassware.

There are five major branches of chemistry:

Organic chemistry focuses on the structure, properties, and preparation of chemical compounds that consist primarily of carbon and hydrogen.

Inorganic chemistry deals with the properties and behavior of inorganic compounds.

Analytical chemistry involves the qualitative and quantitative determination of the chemical components of substances.

Physical chemistry studies the effect of chemical structure on the physical properties of a substance.

Biochemistry is the study of chemical reactions that take place in living things.

Thus, although there are five main branches of chemistry, there are many sub-branches such as quantum chemistry, surface chemistry, environmental chemistry, solid-state chemistry, organometallic chemistry, nuclear chemistry, polymer chemistry and many others.

There is a huge overlap between chemistry and biology, medicine, physics, geology, and many other disciplines.