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Chemical Equations

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A chemical equation represents a chemical reaction. Reactants are shown on the left side of an arrow and products on the right.

In a chemical reaction atoms are neither created nor destroyed; they are merely rearranged. A balanced chemical equation gives the relative numbers of reactant and product molecules.

The chemical equation for a reaction provides us with two important types of information.
  1. The identities of the reactants and products.
  2. The relative numbers of each.

What is a Chemical Equation?

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Chemical equations are the best way we have to represent what happens in chemical reactions at the nanoscopic level that we cannot see. An equation will not be faithful to reality if the chemical formulas are wrong or if the equation is not balanced.

Chemical Equation Definition


A chemical equation is a way of describing what happens in a chemical reaction. The equation also explains the energy terms whether it is absorbed or evolved. The arrow indicates the direction in which the chemical reaction is occurring, it means "yields".

Writing a Chemical Equation


The following are the steps to be taken care while writing a chemical equation.
  1. Classify the reaction type.
  2. Write a qualitative description of the reaction. In this step write the formulas of the given reactants to the left of an arrow and the formulas of the given or predicted products to the right.
  3. Quantify the description by balancing the equation. This can be done by adding the coefficients. By doing this the quantitative description of the reaction should not be changed by adding, removing or altering any formula.

Types of Chemical Reaction

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A chemical reaction is a process in which at least one new substance is produced as a result of chemical change. An almost inconceivable number of chemical reactions are possible. The majority of chemical reactions fall into five categories.

1. Combination Reaction


Combination can also be called synthesis. This refers to the formation of a compound from the union of its elements.

2. Decomposition Reaction


Decomposition or analysis refers to the breakdown of a compound into its individual elements and compounds.

3. Single Replacement Reaction


Single replacement is also called as single displacement. This type can best be shown by some examples where one substance is displacing another.

4. Double Replacement Reaction


Double replacement is also called double displacement because there is an actual exchange of partners to form new compounds.

5. Combustion Reaction


A combustion reaction is the process of burning most combustion involve reaction with oxygen. Combustion reactions are a special class of oxidation-reduction reactions.

Types of Chemical Reaction

Solving Chemical Equations

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To solve the chemical equation we can interpret a chemical equation either in terms of numbers of molecules or in terms of numbers of moles, depending on the needs.

How to Solve Chemical Equations?


The steps to be carried out while solving a chemical equations are
  1. Identify the reaction. (equation)
  2. Write the skeleton equation. (unbalanced form)
  3. Balance the equation.

Parts of a Chemical Equation

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Chemical equations describe the chemical state, and physical and energetic transformations associated with a process.
  1. There are three special parts of every chemical equation, reactants the process (arrow) and product.
  2. Equations can also have different information such as free energy, enthalpy, or stoichiometric variables associated with them. This extra information is generally written to the right of the equation.
  3. All chemical equations balance: all material and energy accounted for on both sides of the equation.

Chemical equations have a formalism associated with them and it is depicted diagrammatically below.

Chemical Reaction Parts

Apart from this there are many symbols used in chemical equation which has unique identification. They are listed below.

Symbol Meaning
+ Plus or added to (placed between substances)
$\rightarrow$
Yields, produces (points to products)
(s) Solid state (written after a substance)
(l) Liquid state (written after a substance)
(g) Gaseous state (written after a substance)
(aq) Aqueous state (written after a substance)
$\Delta$
Heat is added (when written above or below arrow)
The word "reduction" is defined to mean "the gain of electrons". In chemical systems these two processes must occur simultaneously and the number of electrons lost in the oxidation must be same as the number of electrons gained in  the reduction reaction.

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