STOICHIOMETRY

STOICHIOMETRY

von Femosky110 am 12.06.2020 01:09

STOICHIOMETRY AND CHEMICAL REACTIONS
Stoichiometry is a branch of chemistry that is concerned with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relationship among quantities of reactants and products characteristically form a ratio of positive numerals. For instance, in a chemical reaction that forms ammonia (NH3), precisely 1 molecule of nitrogen gas (N2 ) reacts with 3 molecules of hydrogen gas (H2) to generate 2 molecules of NH3 . See below:

 

N

2 + 3H

2 → 2NH

3

This type of stoichiometry which describes the quantitative relationships between substances when they take part in chemical reactions is referred to as reaction stoichiometry. In the above sample reaction, reaction stoichiometry explains the 1:3:2 molecular rations of nitrogen, hydrogen, and ammonia.

Stoichiometry can be employed to estimate quantities like the amount of products in mass, moles and volume that can be produced with given reactants and percentage yield. This means the percentage of the particular reactant that is converted into the product. Stoichiometry extimations can guess the way elements and components diluted in a standard solution react in experimental conditions.

Stoichiometry is founded on the law of conservation of mass which states that the mass of all the reactants in a chemical reaction is equivalent to the mass of the products.

Composition stoichiometry explains the quantitative (mass) relationships between elements that make up a compound. For instance, composition stoichiometry explains the nitrogen to hydrogen ratio in the compound ammonia (NH3): 1 mol of ammonia is composed of 1 mol of nitrogen and 3 mol of hydrogen. As the nitrogen atom is roughly 14 times heavier than the hydrogen atom, the mass ratio is 14:3; consequently 17 kg of ammonia is composed of 14 kg of nitrogen and 3 kg of hydrogen.

A stoichiometric amount or stoichiometric ratio of a reagent is the most favorable amount or ratio at which the reaction proceeds to completion and in which

1. Every one of the reagent is used up

2. There is no shortage of the reagent

3. There is no surplus of the reagent.

A non-stoichiometric mixture, which the chemical reaction has reached the completion, is liable to have only the restrictive reagent consumed completely.

Although nearly all chemical reactions possesses integer-ratio stoichiometry in amount of matter units -moles, number of particles, a few non stoichiometric compounds that cannot be shown ratios of distinct intergers are available. These substances, consequently, go against the law of definite proportions that forms the foundation of stoichiometry together with the law of multiple proportions.

Gas stoichiometry deals with reactions involving gases, where the gases are at a known temperature, pressure, and volume, and can be assumed to be ideal gases. For gases, the volume ratio is ideally the same by the ideal gas law, but the mass ratio of a single reaction has to be calculated from the molecular masses of the reactants and products. In practice, due to the existence of isotopes, molar masses are used instead when calculating the mass ratio.

Laws of chemical combination
It was an Englishman of the 17th century known as Robert Boyle who after his research and findings on the behaviour of gases, made available an unambiguous evidence for the atomic composition of matter. He was the foremost to describe an element as a material that cannot be chemically broken down into a simper form. He was of the opinion that a number of dissimilar elements might exist in nature.

Laws of chemical combination
The fundamental laws of chemical combination are:

• The law of conservation of mass

• The law of constant composition, and

• The law of multiple proportions.

The law of conservation of mass
This law states that the mass of a closed system will stay constant over time, in spite of the processes acting within the system. A comparable statement is that mass cannot be created/destroyed, despite the fact that it can change into one form or the other. This means for any chemical process in a stopped up system, the mass of the reactants must be the same with the mass of the products.

Law of constant composition
The law of constant composition states that the composition of a particular substance is always the same, in spite of the way the substance was made or wherever the substance exists. If take water for instance, it is known that a molecule of water always consist of 2 atoms of hydrogen and 1 atom of oxygen. Whenever the composition of a molecule alters, the result will no longer be the same substance but a different one possessing different properties.

The law of multiple proportions
The law of multiple proportions states that when elements combine to form compounds they do so in a ratio of minute whole numbers. For instance carbon and oxygen react to form CO or CO2, but not in fractions like CO1.2. In addition, the law states that if two elements form more than one compound between them; then the ratios of the masses of the second element united with a fixed mass of the foremost element will as well exist in ratios of small non-fractional integers.

Types of Chemical Equations
A chemical equation is composed of chemical formulas of the reactants -the reacting substances and the chemical formula of the products- the substances created during the chemical reaction. The two are alienated by an arrow symbol which is normally read as "yields" and every individual substance's chemical formula is alienated from the rest by a plus sign.

For an example, the equation for the reaction of hydrochloric acid with sodium can be shown as:

2 HCl + 2 Na → 2 NaCl + H2

It is highly crucial for a chemist to be capable of writing accurate balanced equations and to interpret equations written by others. It is also extremely useful for him or her to be aware of the way to foretell the products of some specific types of reactions.

A Chemical Equation shows:

1. The reactants which combine together in the reaction.

2. The products which are created by the reaction.

3. The amounts of every substance used and every substance formed.

Two significant principles to bear in mind when writing a chemical equation:

1. Every chemical compound has a formula which cannot be changed.

2. A chemical equation gives account of all the atoms used in the chemical reaction. This is an application of the Law of Conservation of Matter. It states that in a chemical reaction atoms are neither created nor destroyed.

C. A few things to bear in mind about writing equations:

1. The diatomic elements when they stand alone are always written as H2, N2, O2, F2, Cl2, Br2 and I2

2. The sign, →, is used to denote "yields" and illustrates the direction of the action.

3. A minute delta, ( ), on top of the arrow illustrates that heat has been supplied.

4. A double arrow, ↔, illustrates that the reaction is reversible and can move in both directions.

5. Before starting to balance an equation, crosscheck every one of formulas to ensure that they are right. You must never alter a formula all through the balancing of an equation.

6. Balancing of an equation is done by putting coefficients in front of the formulas to make sure you have got equivalent number of atoms of everyone of the element on the two sides of the arrow.

Four basic types of chemical reactions
A. Synthesis or composition reaction:

• In this type of reaction, two or more elements or compounds may mingle to form a more complex compound.

The basic formula for this type of reaction is : A + X → AX

Some instances of synthesis reactions are:

1. Metal + oxygen → metal oxide

EX. 2Mg(s) + O2 (g) → 2MgO(s)

2. Non-metal + oxygen → nonmetallic oxide

EX. C(s) + O2(g) → CO2(g)

3. Metal oxide + water → metallic hydroxide

EX. MgO(s) + H2O(l) → Mg(OH)2(s)

4. Non-metallic oxide + water → acid

EX. CO2(g) + H2O(l) → ; H2CO3(aq)

5. Metal + non-metal → salt

EX. 2 Na(s) + Cl2(g) → 2NaCl(s)

6. A few nonmetals combine with each other.

EX. 2P(s) + 3Cl2(g) → 2PCl3(g)

You ought to know these two reactions and try to remember them:

N2(g) + 3H2(g) → 2NH2(g)

1. NH3(g) + H2O(l) → NH4OH(aq)
B. Decomposition reaction:

• In a decomposition reaction, one compound breaks down into its component parts or simpler compounds.

Basic equation formula for this type of reaction is AX → A + X

Some instances of decomposition reactions are

1. Metallic carbonates, when heated, form metallic oxides and CO2(g).

EX. CaCO3(s) → CaO(s) + CO2(g)

2. The majority metallic hydroxides, when heated, decompose to form metallic oxides and water.

EX. Ca(OH)2(s) → CaO(s) + H2O(g)

3. Metallic chlorates, when heated, decompose to form metallic chlorides and oxygen.

EX. 2KClO3(s) → 2KCl(s) + 3O2(g)

4. Some acids, when heated, decompose to form non metallic oxides and water.

EX. H2SO4 → H2O (l) + SO3(g)

C. Replacement reaction:

• A more reactive element takes the place of another element in a compound and frees the less active one.

• Basic form: A + BX → AX + B or AX + Y → AY + X

Examples of replacement reactions
1. Replacement of a metal in a compound by a more active metal.

EX. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

2. Replacement of hydrogen in water by an active metal.

EX. 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

EX. Mg(s) + H2O(g) → MgO(s) + H2(g)

3. Replacement of hydrogen in acids by active metals.

EX. Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

4. Replacement of nonmetals by more active nonmetals.

EX. Cl2(g) + 2NaBr(aq) → 2NaCl(aq) + Br2(l)

D. Ionic:

• This takes place among ions in aqueous solution. The reaction will take place when one pair of ions approach together to create at least one among the following:

1. a precipitate

2. a gas

3. Water or a number of other non-ionized substances.

Basic form of the equation: AX + BY → AY + BX

Some examples of ionic reactions:

1. Formation of precipitate.

EX. NaCl (aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

EX. BaCl2(aq) + Na2SO4(aq) → 2NaCl(aq) + BaSO4(s)

2. Formation of a gas.

EX. HCl(aq) + FeS(s) → FeCl2(aq) + H2S(g)

3. Formation of water. When a reaction takes place between an acid and a base, the reaction is known as a neutralization reaction.)

EX. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

EMPIRICAL AND MOLECULAR FORMULAE
The empirical formula of a compound is the simplest formula of that compound. A molecular formula is the equivalent to or is a multiplication of the empirical formula, and is focused on the definite number of atoms of every type in the compound. For instance, if the empirical formula of a compound is C3H8, its molecular formula might be be C3H8 , C6H16 and so on .