Chemical Reaction and Chemical Equation ~ NEET chemistry

What happens to matter when it undergoes chemical changes? The Law of conservation of mass says that "Atoms are neither created nor destroyed during any chemical reaction " Thus, the same collection of atoms present after a reaction as before the reaction. The changes occur during reaction just involve the rearrangement of atoms. In this section we will discuss:-

Content :

What is a chemical reaction? Explain with examples.
Is substrat a reactant?
Reactant of Photosynthesis reaction.
What does product mean in chemistry?
What is Stoichiometry coefficient?
How do you solve a stoichiometry coefficient?
What is the significance of stoichiometry coefficient?
Characteristics of chemical reaction.
How do you represent a chemical reaction in chemistry?
Types of Chemical Reaction.

Combination Reaction
Decomposition Reaction

(a) Thermal decomposition
(b) Electrolytic decomposition

(c) Photo decomposition

Displacement Reaction
Double Displacement

(a) Neutralisation Reaction
(b) Precipitation Reaction

Combustion Reaction
Oxidation Reaction

(a) Effects of Oxidation Reaction. in our daily Life

(I) Corrosion

√ corrosion of copper

√ corrosion of silver metal

(ii) Rusting

(iii) Rancidity

Reduction Reaction
Redox Reaction

(a) oxidising sgent

(b) reducing agent

Exothermic Reaction
Endothermic Reaction

11. What is a Chemical equation?

(a) Un Balanced Chemical equation

(b) Balanced Chemical equation

12. How to balance a chemical equation?

13. What happens if a chemical equation. is not balance?

14. Why do we balance Chemical. Equation?

15. Can all chemical equation be. balanced?

16. What three things does a balanced. equation show?

What is a chemical reaction?

The transformation of Chemical substance into another chemical substance is known as chemical reaction.

For example : Rusting of iron

Setting of milk into curd

Digestion of food

Respiration

Thier are several definition of chemical reaction :

A chemical reaction involves, breaking and making of bonds between reactants to give rise to formation of new products. A chemical reaction is basically rearrangement of atoms. The breaking and formation of bonds involves energy.

Chemical reaction is a process in which one or more substances called reactants, are converted to one or more different substances called products.

A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

A chemical reaction is described by a chemical equation that gives the identities and quantities of the reactant and products.

Burning of a coal

What is Reactant?

Reactant is a substance that makes part in a chemical reaction. In other words, The substance to the left of the arrow called Reactant.

For example : (a) Hydrogen and oxygen react with each other and form water.

2 H2 + O2 -----------2H2O

Here, hydrogen and oxygen behave as a reactant.

(b) The wax of a candle burns in the presence of Oxygen. Here oxygen and air is a reactant in a combustion reaction.

Is a substrate a reactant?

Yes, a reactant in a chemical reaction is called a substrate when acted upon by an enzyme.

For example : The enzyme catalase brings about the reaction by which hydrogen peroxide is decomposed to water and oxygen. Catalase protects cellular organelles and tissue from damage by peroxide which is continuously produced by metabolic reaction.

Enzymes catalyze Chemical reaction by lowering activation energy barriers and converting reaction substrate molecules to products.

Yeast enzyme is used to puffiness for food

Reactants of Photosynthesis

6CO2 + 6H2O + Sunlight and chlorophyll ----------------------------------C6H12O6 + 6O2

When carbon dioxide gas and water react with each other at the presence of sunlight and chlorophyll , it gives Glucose molecules and release oxygen gas.

Here Carbon dioxide and water behave as a reactant.

Photosynthesis process in Leaf

What does product mean in chemistry?

Products are the species formed from chemical reactants.

During a chemical reaction reactants are transformed into products after passing through a high energy transition state.

This process results in the consumption of the reactant.

A product is a substance that is present at the end of a chemical reaction.

The substance to the right of the arrow are called reactants.

For example : The burning of magnesium in the air form magnesium oxide. Here is an example of chemical reaction. Before burning in air, the magnesium ribbon is cleaned by rubbing with sandpaper. This is done to remove the protective layer of basic magnesium carbonate from the surface of the magnesium ribbon.

Burning of coal

Sandpaper which is used to remove magnesium carbonate layer from magnesium ribbon.

Product of photosynthesis process :
Glucose molecule (C6H12O6)

A chemical reaction changes only the distribution of atoms, not the number of atoms.
In above reaction, the same collection of atoms is present after a reaction or before the reaction. These collection or numerical valued Called stoichiometry coefficient.

What is the significance of these number and what is called in these number.
These numerical valued called coefficient or stoichiometry coefficient. So, the question is arises ..............

What is Stoichiometry coefficient?

In Greek, stoikhein means element and metron means measure, so stoichiometry literally translated means the "measure of element "

The stoichiometry coefficient is the number written in front of atom, ion and molecules in a chemical reaction to balance the number of each element on both the reactant and product sides of the equation.

Stoichiometry coefficient mat be in fraction and whole number.

Consistent with the law of conservation of mass, the number of each type of atom are the same on both sides of equations.

For example : when Na atom react with HCl it forms sodium chloride and release hydrogen gas.

2Na + 2HCl --------------------------2NaCl + H2

In above reaction stoichiometry coefficient or each atom are :

Na molecule -----------2

HCl molecule ------------ 2

NaCl molecule -------------2

we consider the equation for the reaction between iron(III) oxide and Aluminium metal.

Fe2O3(s) + 2Al(s)-----------------2Fe(l) + Al2O3(s)

The coefficient in the equation tell us that one mole of Fe2O3 reacts with 2 moles of Aluminium, forming 2 moles of Fe and one mole of Al2O3. We can write the relationships between the Fe2O3 and the Aluminum as the following mole ratio:

One mole Fe2O3 : two mole of Aluminium

using this ratio, we could calculate how many moles of Aluminum are needed to fully react with a certain amount of Fe2O3, or vice versa.

In a chemical reaction, a new substance is formed which is completely different in properties from the original substance, so in a chemical reaction, a chemical change takes place.

Only rearrangement of atoms takes place in a chemical reaction.

How do you solve a stoichiometry problem?

There are four steps in solving a stoichiometry problem:-

Write the balanced chemical equation.
Convert the units of the given substance (A) to moles.
Use the mole ratio to calculate the moles of wanted substance(B)
Convert moles of the wanted substance to the desired units(grams, liter, particles)

What is the significance of stoichiometry coefficient?

Coefficient are important to prove the law of conservation of mass. The coefficient in a balanced chemical equation indicate the relative number of moles of reactants and products. From this information, the components of reactants and products can be calculated.

Coefficient are used in all chemical equation to show the relative amounts of each substance present.

This amount can represent either the relative number of molecules or the relative number of molecules or the relative number of moles.

If number coefficient is shown then a one is assumed.

Characteristics of Chemical Reaction

1. Evolution of gas :- The chemical reaction between zinc and dilute sulphuric acid is characterised by the evolution of H2 gas.

Zn(s) + H2SO4(aq.)-----------ZnSO4(aq.) + H2(g)

2. Change in colour:- The chemical reaction between citric acid and purple coloured potassium permagnet solution is characterized by a change in colour from purple to colourless.

The chemical reaction between SO2 gas acidified potassium dichromate solution is characterized by a change in colour from orange to green.

(3) change in state of substance: The combustion reaction of candle wax is characterized by a change in state from solid to liquid and gas(because the wax is a solid, water formed by the combustion of wax is a liquid at room temperature. Whereas, carbon dioxide produced by the combustion of wax is a gas.) . These are some chemical reaction which can show more than one characteristics.

(4) change in temperature : The chemical reaction between quick lime water to form slaked lime is characterized by a change in temperature (which is a rise in temperature). The chemicals reaction between zinc granules and dilute sulphuric acid is also characterized by a change in temperature (which is a rise in temperature).
(5) Formation of precipitate : The chemical reaction between sulphuric acid and barium chloride solution is characterized by the formation of a white precipitate of barium sulphate.

BaCl2(aq) + H2SO4(aq) ---------------BaSO4(s) + 2HCl(aq)

To make equations more informative :-

Writ the symbols of physical states of substances in a chemical equation. By writing the physical states of substance, a chemical equation becomes more informative.

Gaseous state is represented by symbol (g)
Liquid state is represented by symbol(l)
Solid state is written by symbol (s)
Aqueous solution is written by symbol (aq.)
writing the condition in which reaction takes place. The condition is generally written above or below the arrow of a chemical reaction

Thus, by writing the symbols of the physical state of substance and condition under which reaction takes place, a chemical reaction can be made for information.

How do you represent the chemical reaction in chemistry :

In a chemical reaction, the reactant are written on the left and the products are written on the right.

The coefficient next to the symbols of entities indicate the number of moles of a substance produced or used in the chemical reaction.

The reactants and products are separated by an arrow (usually read aloud as "yield")

Each individual substances chemical formula is separated from others by a plus sign.

The state of matter of each compound or molecule is indicated in subscript next to the compound by an abbreviation in parentheses.

For example :- A compound in the gas state would be indicated by (g) , solid (s), liquid(l) and aqueous (aq.)

CH4(g) + O2( g) ------------------CO2(g) + H2O(l)

This above reaction indicate that O2 and CH4 reacts to form H2O and CO2. It also indicates that two O2 molecules are required for every methane molecule, and that the reaction will form two water molecule and one carbon dioxide molecule for every methane and two oxygen molecule that react.

The equation also identities that all the compound are in the gaseous state.

The stoichiometry coefficient (the number in front of the chemical formula) result from the law of conservation of mass.

Writing and balancing chemical equation is an essential skill for chemistry student. Who must learn to predict the product of a reaction when given only the reactants.

Types of Chemical Reaction

(1) combination reaction : Reaction in which two or more reactants combine to form one product are called combination reaction.

A general combination reaction can be represented by the chemical equation given here:

A + B ------------------AB

A single product is formed from two or more reactants.

For example : When magnesium is burning in the air (O2) magnesium oxide is formed. In this reaction magnesium is combined with oxygen.

Mg(s) + O2(g) -------------------2 MgO(s)

when carbon is burnt in oxygen, carbon dioxide is formed. In this reaction, carbon is combined with oxygen

C(s) + O2(g) --------------------- CO2(g)

H2O (l) + SO3(g) -----------------H2SO4(aq.)

(2) Decomposition Reaction : Reaction in which one compound decomposes in two or more compounds or elements are known as Decomposition Reaction.
A general decomposition reaction can be represented as follows:

AB ------------------A + B

For example : When calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide.

CaCO3(s) ----------------------------CaO(s) + CO2(g)

Respiration is a decomposition reaction in which energy is released.

C6H12O6 + 6O2-----------6CO2 + 6H2O + energy

(a) Thermal Decomposition : The decomposition of a substance on heating is known as Thermal Decomposition.

2Pb(NO3)2(s)---------heat-----------------2PbO(s) + 4NO2(g) + O2(g)

(b) Electrolytic Decomposition : Reaction in which compounds decompose into simpler compounds because of passing of electricity, are known Electrolytic Decomposition. This is also known as Electrolysis.

For example : when electricity is passed in water, it decompose into Hydrogen and oxygen

2H2O(l)----------------------2H2(g) + O2(g)

(c) Photolysis or photo decomposition or photochemical reaction : Reaction in which a compound decomposes because of sunlight are known as Photolysis or photo decomposition reaction .

For example : When silver chloride is put in sunlight, it decomposes into silver metal and chlorine gas.

2AgCl(s)(white) + sunlight ----------------2Ag(s) (grey) + Cl2(g)

2 AgBr-------------------2Ag + Br2

photographic paper has a coat of silver chloride, which turns into grey when exposed to sunlight. It happen because silver chloride is colourless while silver is a grey metal.

(3) Displacement Reaction : One element is displaced by another element.

Zn(s) + CuSO4(sq.) -----------------ZnSO4(aq.) + Cu(s)

A single element replaces a similar element of an adjacent compound.
The chemical reaction in which a more reaction element displaces a less reactive element from a compound is known as Displacement Reaction. Displacement reaction is also known as Substitution reaction or single Displacement or Replacement Reaction. A general displacement reaction represented by using a chemical reaction :

A + BC ----------------AC + B

Displacement reaction takes place only when 'A'is more reactive than B. If 'B'is more reactive than 'A', then 'A'will not displaces 'C'from BC and reaction will not be taking place.

For example : When zinc reacts with HCl, it gives hydrogen gas and zinc chloride.

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

when zinc reacts with copper sulphate, it forms zinc sulphate and copper metal.

Zn(s) + CuSO4(aq) -------------------ZnSO4 + Cu(s)

(4) Double Displacement Reaction: Two ionic compounds exchange ions, producing two new ionic compounds.

AgNO3(aq) + NaCl(aq) ------------AgCl(s) + NaNO3(aq)

HCl(aq) + NaOH (aq) ---------------NaCl(aq) + H2O(l)

Reaction in which ions are exchanged between two reactants forming new compounds are called double displacement reaction.

AB + CD ---------------------AC + BD

For example : When the solution of barium chloride reacts with the solution of sodium sulphate, white PPT of barium sulphate is formed along with NaCl.

BaCl2(aq) + Na2SO4(aq) ---------------BaSO4(s) + 2NaCl(aq)

when sodium hydroxide (a base) reacts with HCl, NaCl and water are formed.

NaOH(aq) + HCl(aq) -----------------NaCl(aq) + H2O(l)

double displacement reaction , in which precipitate is formed, is also known as precipitation reaction. Neutralisation reaction are also example of double displacement reaction.

(a) Precipitation reaction : The reaction in which PPT is formed by the mixing of the aqueous solution of two salts is called precipitation reaction.

AgNO3 (aq) + NaCl(aq) -----------AgCl(s) + NaNO2(aq)

(b) Neutralisation Reaction : The reaction in which an acid reacts with a base to form salt and water by an exchange of ions is called Neutralisation Reaction.

NaOH(aq) + HCl(aq) ------------------NaCl(aq) + H2O(l)

(5) Combustion Reaction :A single element or compound combines with oxygen gas releasing energy. This rapid oxidation is called burning.

For example : C(s) + O2(g) ---------------CO2(g) + energy
2Mg(s) + O2(g) ------------------2MgO(s) + energy

(6) Oxidation Reaction : Addition of oxygen or non metallic elemnt or removal of hydrogen or metallic elemnt from a compound is known as oxidation.
Elements or compounds in which oxygen or non metallic element is added or hydrogen or metallic elemenet is removed are called to be oxidised.
in other words Reaction that involves the gain of oxygen or loss of hydrogen.

C(s) + O2(g) --------------------------CO2 (g)

Effects of Oxidation Reaction in our Daily Life

(I) Corrosion : It is an undesirable change that occurs in metals when they are attacked by moisture, air, acids and bases.

For example : corrosion (Rusting) of iron: - Fe2O3.nH2O(hydrated iron oxide)

The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen, water, acids, gases etc present in the atmosphere is called corrosion.

For example : Rusting of iron

Rusting: Iron when reacts with oxygen and moisture forms red substance which is called Rusting.

4Fe(s) + 3O2(g) + H2O(l) ------------- 2Fe2O3.xH2O (Red hydrated ferric oxide)

The rusting of iron is s Redox Reaction. Corrosion (Rusting) weakens the iron and steel objects and structure such as railways, car bodies, bridges and shipsale.

Methods to prevent Rusting:

(1) By painting

(2) By greasing and oiling

(3) By galvanisation

# corrosion of copper : Copper objects lose their lusture and shine after some time because the surface of these objects acquires a green coating of basic copper carbonate, CuCO3. Cu(OH)2 when exposed to air.

2Cu(s) + CO2(g) + O2(g) + H2O (l) --------- CuCO3.Cu(OH)2.(basic copper carbonate) (green)

# corrosion of silver metal : The surface of silver metal get tarnished (becomes dull) on exposure to air, due to the formation of a coaching of black silver sulphide (Ag2S) on its surface by the action of H2S gas present in the air.

2Cu(s) + H2S (g) -------------------Ag2S(g) + H2(g)

(III) Rancidity.

The taste and odour of food materials containing fat and oil change when they are left exposed to air for a long time.

This is called Rancidity. In the words, Undesirable change that takes place in oil containing food item due to the oxidation of fatty acids.

It is caused due to the oxidation of fat and oil present in food materials.

Methods to prevent Rancidity :

1. By adding anti oxidants to the food material.

2. storing food in the antitight container/vaccume packing.

3. Flushing out air with nitrogen gas.

4. Refrigeration of food stuff.

(7) Reduction Reaction : Addition of hydrogen or metallic element or removal of oxygen or non metallic element from a compound is called Reduction Reaction.

The compound or element which goes under reduction is called to be Reduced.

In other word, reaction that shows the loss of oxygen or gain of hydrogen.

ZnO + C--------------------Zn + CO

Here, ZnO is reduced to Zn that means here reduction takes place.

Carbon is oxidised to CO that means here oxidation takes place.

Redox Reaction

Chemical reaction in which both oxidation and reduction take place simultaneously.

when copper is heated with hydrogen, then copper metal and water are formed.

In this reaction, copper oxide is changing into copper metal and oxygen is being removed from copper oxide. Removal of oxygen from a substance is called Reduction. So, copper oxide is being reduced to copper.

CuO + H2 -------------------------------Cu + H2O

The compound or element whicg goes under reduction is called to be Reduced and the compound or element which goes under oxidation is called to be oxidised.

Therefore, oxidation and reduction takes place in Redox reaction.

In Redox reaction oxidation takes place by oxidising agent and reduction takes place in presence of reducing agent.

(a) Oxidising Agent : The substance which gives oxygen for oxidation is called oxidising agent.

The substance which removes hydrogen is also called an oxidising agent.

2H2 + O2 ----------------2H2O

In this reaction, hydrogen changing to water and oxygen is being added to hydrogen. Addition of oxygen to a substance is called oxidation, so hydrogen is being oxidised to water.

(b) Reducing agent: The substance which gives hydrogen for reduction is called Reducing agent. Or the substance which gets oxidised is called reducing agent.

H2 + Cl2 ---------------2HCl

In the above reaction, hydrogen is added to chlorine to form hydrogen chloride. Thus , Gas is getting reduce to form hydrochloric acid.

Exothermic Reaction

Reaction which produces energy is called Exothermic reactions.

In other words, a chemical reaction in which heat energy is evolved.

C + O2 -----------------------CO2 + heat

Most of the decomposition reaction are Exothermic reaction.

Endothermic Reaction

A chemical Reaction in which heat energy is absorbed. Since, a chemical reaction in which heat energy absorbed is called endothermic reaction.

ZnCO3 + heat ----------------- ZnO + CO2

What is a Chemical Equation?

Chemical reaction can be written in chemical equation form which should always be balanced.

In other word, chemical reaction are represented on paper by chemical equation.

For example : Hydrogen gas can react with oxygen gas to form water. The chemical equation for this reaction is written as:

2H2 + O2 ----------------------2H2O

Chemical formulas aND other symbols are used to indicate the starting materials, or reactants, which by convention are written on the left side of the equation, and the final compounds, or products, which are written on the right. An arrow points from the reactants to the products.

The arrow is read as "yields" or "reacts to form ". Above equation indicate that hydrog6and oxygen yields water. The equation for this reaction is even more informative when written as follows :

2H2(g) + O2(g) ---------------2H2O(l)

A chemical equation is a way to represent the chemical reaction in a concise and informative way.

Types of Chemical Reaction

A chemical equation can be divided into two types :

(A) Unbalanced Chemical reaction :

If the number of atoms of each element is reactant is not equal to the number of atoms of each element present in the product, then the chemical equation is called unbalanced chemical equation.

Fe + H2O -----------------Fe3O4 + H2

In above equation, a number of atoms of elements are not equal on two sides of the reactants. For example, on the left hand side only one iron atom present, while three iron atoms are present on the right hand side. Therefore, it is an unbalanced chemical equation.

Unbalanced chemical equation violate the law of conservation of mass.

(B) Balanced Chemical equation : A balanced chemical equation has the number of atoms of each element equal on both sides.

Zn + H2O -----------------ZnSO4 + H2

In this equation, number of Zinc, hydrogen and sulphate are equal on both sides, so it is Balanced chemical equation.

According to law of conservation of mass, mass can neither be created nor destroyed in a chemical reaction. To obey this law, the total mass of elements present in reactant must be equal to the total mass of elements present in products.

How to balance a chemical equation?

A chemical equation is the chemical formula that provide the information of the elements and molecules that are reacting as well as the molecules that are being produced from that reaction. "The Law of Conservation of Mass" state that the mass of the reactants must balance the mass of the products.

To balance a chemical equation, the atoms of both the elements and molecules on the reactant side (left side) and product side (right side) must be equal to each other.

In this instructable , you will understand and learn how to balance a chemical equation.

For example: The combustion of n-heptane (C7H16) ,an important component of gasoline.

C7H16(l) + O2(g) ---------------CO2(g) + H2O(g)

The complete combustion of any hydrocarbon with sufficient oxygen always yields carbon dioxide and water.

Above reaction is not balanced , the number of each type of atom on the reactant side of the equation (7 carbon atoms, 16 hydrogen atoms and 2 oxygen atoms) is not the same as the number of each type of atom on the product side( one carbon atom, two hydrogen atom and three oxygen atom). Consequently the coefficient of the reactants and products must be adjusted to give the same number of atoms of each type on both sides of the reactants and products are fixed, the equation cannot be balanced by changing the subscripts of the reactants on the products.

The simplest and most generally useful method for balancing chemical equation is "inspection" better known as "trial" or "error" .

The following is an efficient approach to balancing a chemical equation using the method.

Steps in Balancing Equation

Step I : The unbalanced chemical equation is given to you

Heptane burns in the presence of oxygen gives carbon dioxide and water.

C7H16 + O2 ---------------------------CO2 + H2O

Step II : Identify the most complex substance:

The most complex substance is the one with the largest number of different atoms, which is C7H16. We will assume initially that the final balanced chemical equation contains one molecule or formula unit of this substance .

(3) Make a list : First identify the elements on the reactant side(left side) and the elements of the compounds are on the product side (right side )

Make a list of all the elements on each side under the equation for both the reactants and products as shown below :

Under the reactants side, list C,H,O under the products side , list C,H,O

Reactant side atoms. : C --------7

H-------16

O--------2

Product side atoms : C------1

H ------2

O -------3

(4) Adjust the coefficient: Try to adjust the coefficient of the molecules on the other side of the equation to obtain the same number of atoms on both sides. Because one molecule of n- heptane contains seven carbon atoms, we need seven CO2 molecules, each of which contains one carbon atI'm, on the right side.

C7H16 + O2 -------------7CO2 + H2O

(5) Balance Polyatomic ion as a unit : There are no Polyatomic ions to be considered in this reaction.

(6) Balance the remaining atom : Because one molecule of n-Heptane contains 16 hydrogen atoms, we need 8 H2O molecules, each of which contains 2 hydrogen atom, on the right side

C7H16 + O2 ------------------ 7CO2 + 8H2O

The carbon and hydrogen atoms are now balanced, but we have 22 oxygen atoms on the right side only 2 oxygen atoms on the left side. we can balance the oxygen atoms by adjusting the coefficient in front of the least complex substance, O2 on the reactant side.

C7H16 + 11O2 ---------------- 7CO2 + 8H2O

(7) Check your work : The equaroom is now balanced and threw are no fractional coefficient, there are 7 carbon atoms, 16 hydrogen atoms and 22 oxygen atom on each side. Always check to be sure that a chemical equation is balanced.

Balancing equations requires some practice on your part as well as some common sense. If you find yourself using very large coefficient or if you have spend several minutes without success, go back and make sense that you have written the formula of the reactants and products correctly.

For example : Hydroxyapatite

The reacroom of the mineral Hydroxyapatite with phosphoric acid and water gives calcium dihydrogen phosphate monohydrate. Write and balance the equation for this reaction :

Ca(PO4)3(OH)(s) + H3PO4(aq) + H2O(l) ----------------------Ca(H2PO4)2.2H2O(s)

Step I : Identify the most complex substance : We start by assuming that only one molecule or formula unit of the most complex substance Ca5(PO4)3(OH), appears in the balanced chemical equation.

Step II : Adjust the coefficient : Because calcium is present in only one reactant and one product, we begin with it. One formula unit of Ca5(PO4)3(OH) contains 5 calcium atoms, so we need 5 Ca(H2PO4)2.2H2O on the right side.

Ca5(PO4)3(OH) + H2PO4 + H2O -------------- 5Ca(H2PO4)2.H2O

Step III : Balance Polyatomic ions as a unit : It is usually easier to balance an equation if we recogn6that certain combination of atom occur on both sides. In this equation, the Polyatomic phosphate ion (PO4)³- shows up in three places. In H3PO4, the phosphate ion is combined with three H+ ions to make phosphoric acid (H3PO4) whereas in Ca(H2PO4)2.H2O it is combined with two H+ ions to give the dihydrogen phosphate ion.

Thus it is easier to balance PO4 as a unit rather than counting individual phosphorus and oxygen atom. There are 10 PO4 units on the right side but only 4 on the left side.

The simplest way to balance the PO4 units is to place a coeff6of 7 in front of H3PO4

Ca5(PO4)3(OH) + 7H3PO4 + H2O ----------- 5Ca(H2PO4)2.H2O

Although OH-is also a Polyatomic ion, it does not appear on both sides of the equation. so oxygen and hydrogen must be balanced separately.

Step IV : Balance the remaining atoms : We have 30 hydrogen atoms on the right side but only 24 on the left side.

we can balance the hydrogen atoms using the least complex substance, H2O by placing a coefficient of 4 in front of H2O on the left side, giving a total of H2O molecules.

Ca5(PO4)3(OH)(s) + 7H3PO4(aq) +4 H2O(l) ------------------------- 5Ca(H2PO4)2.H2O(s)

The equation is now balanced. Even though we have not explicity balanced the oxygen atoms, there are 45 oxygen atoms on each side.

Step V : Check your work : Both sides of the equation train 5 Calcium atoms, 7 phosphorus atoms, 30 hydrogen atoms and 45 oxygen atoms.

Question : What happens if s chemical equation is not balanced?

Chemical reaction must be balanced, or in other words, must have the same number of various atoms in the products as in the reactant. If a chemical reaction is not balanced, no information about the relationship between products and reactants can be derived.

Question : Why do we balance Chemical equation?

An equation is balanced when the same number of each element is represented on the reactants and products sides. Equations must be balanced to accurately reflect the law of conservation of matter.

Question : Can all chemical equation be balanced?

All chemical equation to be balanced. This means that there must be the same number of each type of atoms on both sides of the arrow. That's because mass is always conserved in chemical reaction.

Question : What three things does a balanced equation show?

When chemical equation is balanced, it is clear what substances are the reactants, which are the products, how much of each substance is involved, as well as their relationship to each other, and the steps that occur during the reaction.

Question : What law is obeyed by a balanced chemical equation?

Law of conservation of mass

Question : Is it possible to have a coefficient of zero in any chemical equation?

The stoichiometry coefficient of any species that does not participate in a given chemical reaction is zero.

Summary

A chemical reaction is described by a chemical equation that gives the identities and quantities of the reactant and product.

In a chemical reaction, one or more substances are transformed to new substance. A chemical reaction is described by a chemical equation., an expression that gives the identities and quantities of the substances involved in a reaction. A chemical equation shows the starting compound (s) - the reactants - on the left and final compound (s) - the products - on the right, separated by an arrow. In a balanced chemical equation, the number of atoms of each element and the total charge are the same on both sides of the equation.

The number of atoms, molecules, or formula units of a reactant or product in a balanced chemical equation is the coefficient of that species. The mole ratio of two substances in a chemical reaction is the ratio of their coefficient in the balanced chemical equation.

A balanced chemical equation shows us the numerical relationship between each of the species involved in the chemical change. We can use these numerical relationship to write mole ratio, which allow us to convert between amounts of reactants and /or products (and thus solve stoichiometry problems!).

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