COMPLETE STUDY MATERIAL ON CHEMICAL EQUATIONS - FOUNDATION TO ADVANCED

CHEMICAL REACTIONS - CHEMICAL EQUATIONS

INTRODUCTION:

In our daily life we all know about physical changes and chemical changes, all these changes are observed in our day today life.  We observe ice converts into water vapor and vice versa.  In this example, the changes in the states of matter are observed and heat may be gained or released.  Similarly, burning of wood also example.

CHEMICAL REACTION:

 Chemical reactions represent the processes in which a single substance or substances undergo change to produce new substance or substances with different or new properties are called 'CHEMICAL REACTIONS'.

For example: When potassium nitrate gets heated potassium nitrite and oxygen are formed.  This is a chemical reaction since potassium nitrate changes into potassium nitrite and oxygen, these are new substances.

A chemical reaction consists of REACTANTS and PRODUCTS.

From the above example, potassium nitrate is called Reactant and potassium nitrite and oxygen are the products, since the substance which takes part in  chemical reaction is called Reactant and a new substance formed or substances formed in a chemical reaction, called products.

FIND OUT THE REACTANTS AND PRODUCTS from the following:

Calcium carbonate ----->  Calcium oxide and carbon dioxide

Sodium combines with water to get sodium hydroxide and hydrogen

HOW THE REACTANTS ARE TRANSFORMED INTO PRODUCTS ??????

Initially, the compounds or molecules break down into atoms and these atoms take part in the reaction then products are formed by new bonds formed between the atoms.

CHARACTERISTICS OF CHEMICAL REACTION:

How can we understand that there is a existence of chemical reaction and it took place, by observing the characteristics we can understand that there is a chemical reaction observed ......

1) When metals react with acids, we can observe there is evolution of Hydrogen gas.

2) Formation of precipitate when two solutions are mixed, the precipitate is a solid substance separated from the solution.  For example, lead iodide is a precipitate formed when lead acetate aq.solution combined with aq. sol. of potassium iodide.

3) Some times we observe the emission of heat such reactions are exothermic reactions, we know that when Calcium oxide is added to water, and sometimes the equipment becomes cold when ammonium chloride mixed with barium hydroxide.  These are called endothermic reactions.

CHEMICAL EQUATIONS  Vs CHEMICAL REACTIONS

We can understand with an example :

CaCO3 is the formula of Calcium carbonate and CaO is calcium oxide and CO2 is carbon dioxide.

The above is a chemical reaction, when it is represented with formula and symbols, that notation is known as chemical equation.

How can we write a chemical equation ??????

* the reactants and products in the reaction should be written with their formulae  or symbols.

* when more than one reactant or product, then + symbol is used

* an arrow mark is used in between reactants and products, the arrow mark also tells us in which way the reaction is taking place.

What information is conveyed by a chemical equation ???


* we understand the reactants and products in the reaction, and their number of atoms

* we can calculate the masses of the compounds or molecules in the reactants and products

* we come to know the number of moles of the reactants and products.

EXAMPLE:

               When we observe the formation of water from hydrogen and oxygen :

There are :

four hydrogen atoms, two oxygen atoms gives two water molecules

two moles of hydrogen and one mole of oxygen to give two mole of water

four grams of hydrogen and thirty two grams of oxygen to give 36 g of water

we can also calculate number of atoms and volumes also.

             2 H2 + O2 ------> 2 H2O

HOW TO MAKE A CHEMICAL EQUATION MORE INFORMATIVE ???

Generally,  a chemical equation do not represent any thing other than the reactants and products, but to make a chemical equation more informative, one has to represent :

* states of the reactants and products, s, l, g, aq.

* the evolution of gas with upward arrow line and precipitate with downward arrow line

* if heat is liberated, then in the products + heat should be written

* if heat is absorbed, then in the reactants + heat should be written.

TYPES OF CHEMICAL REACTIONS:

1) COMBINATION REACTIONS

2) DECOMPOSITION REACTIONS

3) SINGLE DISPLACEMENT REACTIONS OR SUBSTITUTION REACTIONS

4) DOUBLE DISPLACEMENT REACTIONS


WHAT IS THE DIFFERENCE BETWEEN BALANCED CHEMICAL EQUATION AND UNBALANCED CHEMICAL EQUATION ??


BALANCED CHEMICAL EQUATION : When the number of atoms of each element on both sides is  equal then the equation is said to be balanced chemical equation.

UNBALANCED CHEMICAL EQUATION: When the number of atoms of each element on both sides is not equal, then the equation is said to be unbalanced chemical equation.

HOW TO MAKE AN EQUATION A BALANCED EQUATION - STEPS TO BE REMEMBERED:

** must know the formulae of compounds or molecules of reactants or products and the subscriptions in the formulas should not be altered at any cost.

for example: always the calcium carbonate is CaCO3 and Hydrogen molecule  is H2 only.

TRIAL AND ERROR METHOD OF BALANCING A CHEMICAL EQUATION:


STEPS:

1) COUNT EACH TYPE OF ATOMS ON BOTH SIDES

2) IDENTIFY THE MOST COMPLICATED FORMULA AND COUNT THE NUMBER OF ATOMS OF EACH ELEMENT

3)  BY TRIAL AND ERROR METHOD, CHANGE THE NUMBER OF ATOMS ON BOTH SIDES TILL THE NUMBER OF ATOMS ON BOTH SIDES EQUAL.

EXAMPLES OF UNBALANCED AND BALANCED EQUATIONS:

1) KClO3 ---> KCl + O2

 After balancing,

   2KClO3 ----> 2 KCl + 3 O2



2) CaCO3 ---> CaO + CO2



 3) AlCl3 + Ca(OH)2  ----> Al(OH)2 + CaCl2


    2 AlCl3 + 3 Ca(OH)2  ----> 2 Al(OH)2 + 3 CaCl2

4) Al + H2SO4 ----> Al2(SO4)3   +  H2

After balancing:

2 Al + 3 H2SO4 ----> Al2(SO4)3   +  3 H2

How to balance a chemical equation? with algebraic expression method.

A chemical equation tells us the type of reaction between different reactants. Chemical equation gives the states of the reactants and products.  One can calculate the amount of products required for required amount of products.

To balance a chemical equation, very interesting method is algebraic expression method.


for example:  C3H8 + O2 -----> CO2  + H2O




The above reaction is to be balanced using algebraic expressions

step 1) the coefficients of Each reactants and products assumed to be a,b,c,d,...

                    aC3H8 + b O2 -----> c CO2  + d H2O

step 2) identify and count the number of elements on both sides of the reaction

                    carbon: 3a = c

                    hydrogen: 8a = 2d

                    oxygen:  2b = 2c + d

                    

step 3) let us assume a=1, then simplify the equations for other variable values

                        c = 3,     2d = 8   then d = 4             if d=4 and c =3 then 2b=6 + 4 = 10, b=5

step 4) write the chemical equation using the variable values

            C3H8 + 5O2 ---> 3CO2  + 4 H2O



step 5) count the number of atoms on both sides

                   carbon atoms  = 3
                  hydrogen atoms = 8
                  oxygen atoms = 10 





step 6) we conclude that the equation is said to be balanced. 

ASSIGNMENT ON BALANCING CHEMICAL EQUATIONS:

1) Reaction between Iron oxide and carbon to get Iron and carbon dioxide

2) reaction between hydrogen and oxygen to get water

3) reaction between acetic acid and ethyl alcohol to get ethyl acetate and water

4) when sulphuric acid reacts with calcium carbonate to get calcium sulphate along with H2CO3

5) combustion of methane to get carbon dioxide and water

6) reaction between copper oxide and sulphuric acid to get copper sulphate and hydrogen

7) reaction between nitrogen and oxygen

8) reaction between ammonia and oxygen

9) reaction between nitrogen and hydrogen

10) when ammonia reacts with hydro chloric acid to get ammonium chloride

11) when sodium reacts with water to get sodium hydrogen and hydrogen

12) when calcium reacts with hydro chloric acid to get calcium chloride and hydrogen

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LABORATORY APPARATUS - USES

LABORATORY APPARATUS - HOW TO USE AND WHAT ARE THEIR ADVANTAGES ?

1, I am ‘Test tube’…..!

A test tube is a clear glass or plastic container that is much longer than its wide, commonly has a U-shaped bottom and has an open top.  Glass and special plastic test tubes are also non-reactive.  Many metals react with all sorts of chemicals in ways that would ruin an experiment or sample. 

Chemists use test tubes to mix, heat and/or hold small quantities of chemicals for assays and laboratory experiment.  Biologists use them to culture and handle various organisms, fluids, and samples.

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2.  I am ‘Beaker’

 

A Beaker is a common container in most labs.  It is used for mixing, stirring, and heating chemicals.   It is generally a cylindrical container with a flat bottom.  Most also have a small spout to aid pouring.  Beaker is distinguished from a flask, by having straight rather than sloping slides.  Beakers are available in glass, and also in metal, plastics.  

Any experiment which yields a liquid product uses a beaker to catch the liquid.

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3. CONICAL FLASK

SK’mCAn Erlenmeyer flask also known as a Conical Flask or a titration flask, which features a flat bottom, a conical body, and a cylindrical neck.  It is named after the German Chemist Emil Erlenmeyer (1825-1909), who created in 1860.

Erlenmeyer flasks have wide bases, with sides that taper upward to a short vertical neck.  They may be graduated, and often spots of ground glass or enamel are used.  It differs from the beaker in its tapered body and narrow neck.  Depending on the application, they may be constructed from glass or plastic in a wide range of volumes. The mouth of the Erlenmeyer flask may have a beaded lip that can be stopped or covered.

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4.  I am watch glass….

A watch glass is a circular concave piece of glass used in chemistry as a surface to evaporate a liquid., to hold solids while being weighted, for heating a small amount of substance and as a cover for a beaker.  It can be used to prevent dust or other particles entering the beaker, the watch glass does not completely seal the beaker, so gas exchanges still occur.  When used as an evaporation surface, a watch glass allows closer observation of precipitates or crystallization.

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5. PIPPETTE

Pipette or pipet is a laboratory tool commonly used in chemistry, biology, and medicine to transport a measured volume of liquid. 

Pipette works by creating a partial vacuum above the liquid –holding chamber and selectively releasing this vacuum to draw up and dispense liquid. 

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6. RUBBER STOPPERS

•Rubber stoppers in the labs are used frequently to plug flasks and test tubes.  Its purpose is to prevent liquids, and gases, escaping from their containers and also to prevent contaminants from entering the containers.
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7. ROUND BOTTOM FLASK/ROUND BOTTOMED FLASK

   

   A GLASS FLASK USED IN LABORATORY FOR HOLDING CHEMICAL LIQUIDS AND SOLUTIONS, WHICH HAS A SPHERICAL SHAPE BODY FOR UNIFORM HEATING AND HAS CYLINDRICAL NECK. IT IS ALSO KNOWN  AS A BOILING FLASK, MOST OFTEN USED WHEN HEATING SOLUTIONS, PARTICULARLY FOR DISTILLATION. 

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8. FUNNEL

Glass funnels can be used to guard against spillage when pouring chemicals from one vessel to another, can be fitted with filter to separate solids from liquids. 

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9. GRADUATED CYLINDER

•A graduated cylinder also called as measuring cylinder, used to measure the volume of liquids.  It is used accurately to measure the volume of chemicals for use in reactions.

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