What is a balanced chemical equation why should chemical equation be balanced Brainly

Last updated at March 26, 2022 by Teachoo

Answer

A balanced chemical equation has an equal number of atoms of different elements in reactants and products.

No. of atoms of elements in Reactants = No. of atoms of elements in Products

For eg, 

Fe 2 O 3 + 2Al  →  Al 2 O 3 + 2Fe

Number of atoms of Fe in reactants = Number of atoms of Fe in products = 2

Number of atoms of O in reactants = Number of atoms of O in products = 3

Number of atoms of Al in reactants = Number of atoms of Al in products = 2

• An unbalanced chemical equation is not an accurate representation of a chemical equation and thus it requires balancing.
• Chemical reactions should be balanced in order to obey the law of conservation of mass , which states that mass can neither be created nor be destroyed.
• Hence, the total mass of substances before the chemical reaction should be equal to the total mass of reactants after the reaction .

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A balanced equation is an equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charge is the same for both the reactants and the products. In other words, the mass and the charge are balanced on both sides of the reaction.

Also Known As: Balancing the equation, balancing the reaction, conservation of charge and mass.

An unbalanced chemical equation lists the reactants and products in a chemical reaction but doesn't state the amounts required to satisfy the conservation of mass. For example, this equation for the reaction between iron oxide and carbon to form iron and carbon dioxide is unbalanced with respect to mass:

Fe2O3 + C → Fe + CO2

The equation is balanced for charge because both sides of the equation have no ions (net neutral charge).

The equation has 2 iron atoms on the reactants side of the equation (left of the arrow) but 1 iron atom on the products side (right of the arrow). Even without counting up the quantities of other atoms, you can tell the equation isn't balanced.

The goal of balancing the equation is to have the same number of each type of atom on both the left and right sides of the arrow. This is achieved by changing the coefficients of the compounds (numbers placed in front of compound formulas). The subscripts (small numbers to the right of some atoms, as for iron and oxygen in this example) are never changed. Changing the subscripts would alter the chemical identity of the compound.

The balanced equation is:

2 Fe2O3 + 3 C → 4 Fe + 3 CO2

Both the left and right sides of the equation have 4 Fe, 6 O, and 3 C atoms. When you balance equations, it's a good idea to check your work by multiplying the subscript of each atom by the coefficient. When no subscript is cited, consider it to be 1.

It's also good practice to cite the state of matter of each reactant. This is listed in parentheses immediately following the compound. For example, the earlier reaction could be written:

2 Fe2O3(s) + 3 C(s) → 4 Fe(s) + 3 CO2(g)

where s indicates a solid and g is a gas.

In aqueous solutions, it's common to balance chemical equations for both mass and charge. Balancing for mass produces the same numbers and kinds of atoms on both sides of the equation. Balancing for charge means the net charge is zero on both sides of the equation. The state of matter (aq) stands for aqueous, meaning only the ions are shown in the equation and that they are in the water. For example:

Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) → AgCl(s) + Na+(aq) + NO3-(aq)

Check that an ionic equation is balanced for the charge by seeing if all the positive and negative charges cancel each other out on each side of the equation. For example, on the left side of the equation, there are 2 positive charges and 2 negative charges, which means the net charge on the left side is neutral. On the right side, there is a neutral compound, one positive, and one negative charge, again yielding a net charge of 0.

Take for example the combustion of methane (#"CH"_4"#):

#"CH"_4"# + #"O"_2"# #rarr# #"CO"_2"# + #"H"_2"O"#

If you count the number of atoms (subscripts) of carbon, hydrogen, and oxygen on both sides of the equation, you will see that on the reactant side (left side), there are one atom of carbon, four atoms of hydrogen, and two atoms of oxygen.

On the product side (right side), there are one atom of carbon, two atoms of hydrogen, and three atoms of oxygen. Therefore, the equation does not satisfy the law of conservation of mass, and is not balanced.

In order to balance the equation, we must change the amounts of the reactants and products, as necessary, by adding coefficients in front of the appropriate formula(s).

When balancing an equation, NEVER change the subscripts, because that changes the substance. #"H"_2"O"# is NOT the same substance as #"H"_2"O"_2"#. To determine the number of atoms of each element, the coefficient is multiplied times the subscripts in each formula. If there is no coefficient or subscript, it is understood to be 1. The balanced equation for the combustion of methane is:

#"CH"_4"# + #2"O"_2"# #rarr# #"CO"_2"# + #"2H"_2"O"#

If you compare the unbalanced equation to the balanced equation, you will see that the chemical formulas of each reactant and product were not changed.

The only change is the coefficient of 2 written in front of the formula for oxygen on the reactant side, and the coefficient of 2 written in front of the formula for water on the product side.

So now there are one carbon atom, four hydrogen atoms, and four oxygen atoms on both sides of the equation, and the equation is balanced. Now the equation says that "One molecule of methane plus two molecules of oxygen produce one molecule of carbon dioxide and two molecules of water".

When working with moles, the equation would be read as "One mole of methane plus two moles of oxygen produce one mole of carbon dioxide and two moles of water".

Here is a video which discusses the importance of balancing a chemical equation.

Video from: Noel Pauller