A chemical reaction is a chemical change which results in the formation of one or more products. The initial reactants differ in physical or chemical characteristics from the products formed. Chemical reactions generally involve either the formation or the breaking of chemical bonds.
Combustion
When oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat.
Synthesis
When two or more simple compounds combine to form a more complicated one. This is also known as a direct combination reaction.
A + B → AB
For example, iron and sulfur combine in a synthesis reaction to form iron (II) sulfide:
8Fe + S8 → 8FeS
Decomposition
The opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. This is also known as an analysis reaction.
AB → A + B
For example:
Cu(CO3) → CuO + CO2
2H2O → 2H2 + O2
Single displacement (Substitution)
When one element trades places with another element in a compound. In these kinds of reactions one element displaces another form a compound to form a new compound and the displaced element. Generally the more reactive elements displace the less reactive element in a compound.
A + BC → AC + B
For example:
Zn + H2SO4 → ZnSO4 + H2
Zn + 2 HCl → ZnCl2 + H2
Double displacement (Metathesis)
When the anions and cations of two different molecules switch places, forming two entirely different compounds. In these kinds of reactions the two reacting compounds exchange their radicals or ions to form two new compounds.
AB + CD → AD + CB
For example:
ZnO + 2HCl → ZnCl2 +H2O
NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
Acid-base
A special kind of double displacement reaction that takes place when an acid and base react with each other. As the name suggests, these kinds of reactions occur between an acid and a base. It is a neutralization reaction and is characterized by the formation of a salt and water. The hydronium (H+) ion in the acids reacts with the hydroxide (OH-) ion in the base to form these products.
HA + BOH → H2O + BA
For example:
HCl + NaOH → NaCl + H2O
HBr + NaOH → NaBr + H2O
Redox (Oxidation - Reduction)
In these kinds of reactions both oxidation and reduction take place simultaneously in the reaction. Oxidation is characterized by loss of electrons while reduction is characterized by gain of electrons. Here I2 is reduced to I- and S2O32- is oxidized to S2O42-:
2S2O32−(aq) + I2(aq) → S4O62−(aq) + 2I−(aq)
Hydrolysis
This reaction involves water.
X-(aq) + H2O(l) ↔ HX(aq) + OH-(aq)
Isomerization
In these type of reaction, the structural arrangement of a compound is altered. For example:
CH3-CH2-CH2-CH3 → CH3-CH3-CH-CH
Объяснение:
лемент хром расположен в четвертом периоде и побочной подгруппе VI группы Периодической системы. Атом хрома имеет электронную конфигурацию . Обратите внимание на провал электрона: подобно другим элементам шестой группы в соединениях хром проявляет максимальную степень окисления +6, однако наиболее устойчив в более низкой степени окисления +3.
Элемент хром был обнаружен в природном минерале в конце XVIII века. Тогда же были получены его соли, яркая и разнообразная окраска которых и объясняет данное элементу название – оно происходит от греческого слова "chroma" - цвет, краска.
Нахождение в природе и получение
В природе встречается преимущественно в виде двойного оксида – хромистого железняка , переработкой которого и получают металл. Восстановление хромистого железняка углем в электрических дуговых печах приводит к феррохрому – сплаву железа и хрома:
Объяснение:
объем газа теоретический V=4,704/0,7 = 6,72 л
количество вещества газа n =6,72/22,4 = 0,3 моль
СnH2n+1COONa + NaOH> СnH2n+2 + Na2CO3
n соли = 0,3 моль
М соли =28,8/0,3 = 96 г/моль
М соли =14n +1+12+32+23
14n +68 =96
n=2
ответ: газ - этан С2Н6