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Examples of Chemical Changes in Everyday Life

We all must have seen the fireworks, the dazzling sparkles of different colors such as red, white and blue trickling down in all directions. The fireworks are an example of chemical change or chemical reaction. 
In any chemical reaction, the reacting substance gets converted into another new substance.
Overall, this involves in the production of a newer substances along with newer set of physical as well as chemical properties.
But how could we decide whether a change that has occurred is really a chemical reaction or not? 
In our everyday life we witness a lot of chemical changes if we have notice them carefully. 

Let’s take some examples; Have you ever seen an autumn leaf? It actually shows some change in colour from the original green to either red or orange. 
This change in colour is a clue to some chemical changes that occurs during the autumn season and the change in temperature is responsible for the colour change in the leaves. Hence colour change is an indication of chemical reaction. 
All chemical changes are also associated with energy changes. 
The energy could be absorbed in like the baking of cake where energy is absorbed in by the batter or in cases where the energy could also be released as in the in the case of fireworks.  

Have you ever smelt a rotten egg? We can easily observe that they smell completely different from that of fresh eggs. There is a chemical change during the spoilage of eggs and it is evident in any kind of food materials which has odour. 
When we smell an odd odour in food materials left outside for few days (such as chicken, pork of mayonnaise), we know that the food has undergone some chemical change. 

Chemical change is also associated with the change in composition of a substance. 
As wood burns, it turns into ashes and gases. Wood cannot be restored back to its original form and this shows that there indeed is a chemical change. 
Do you think any chemical reaction is possible in plants? The answer is ‘YES’. Photosynthesis is a series of chemical reactions that allow plants to uses sunlight and create carbohydrates. 
In this process plants use light energy to make sugar and oxygen gas from carbon dioxide and water. 

Any form of digestion is also a chemical reaction. Digestion starts when we chew and mix the food with the saliva in our mouth and the process continues all the way down to our intestine. From mouth to intestine, food undergoes different chemical changes and provide energy to our body. 
When we burn Bunsen burner in lab, we are carrying out chemical reaction that produces water vapor and carbon dioxide. 
We all must have witnessed the rusting of our car and the burning of magnesium metal in oxygen to form magnesium oxide in our daily life are also a chemical reaction.
Several environmental changes which occur in our surroundings such as thunderstorm, lightening and rain are also examples of chemical changes only. 

The acid rain which happens due to presence of sulphur dioxide and nitrogen oxides is also an example of chemical change. No doubt this chemical change shows negative impact on nature and alters the pure form of water. 
Both of these oxides react with rain water to form acids like nitrous, nitric, sulphurous and sulphuric acids which come out with water. 
Acid rain is not a natural normal phenomenon and is a result of industrial pollution caused by us and we must take preventive measures. 
The heat and light of the Sun is due to the presence of hydrogen and helium gases which involve in nuclear fusion reaction and release an enormous amount of energy in the form of light and heat. 

There are several chemical changes which occur in our body also such as human brain is composed of a trillion neurons. 
Each of the neuron is connected with each other through a synapse. The response of our body on any of the stimulus is also related to chemical change only. The brain is able to decipher an impulse when an electrochemical wave travels along the neuron to a synapse. When the wave reaches a synapse, it provokes release of a chemical or neurotransmitter. The chemical neurotransmitter molecules bind to chemical receptor molecules located in the membrane of another neuron, on the opposite side of the synapse and the impulse is transmitted. 

Digestion of food in stomach is also a chemical change which involves cleavage of complex food in the presence of enzymes. The complex food in our body is nothing but biological molecules such as sugar molecules, proteins and lipid. Any change which cannot change the chemical composition of the initial chemical substance or cannot form a new chemical substance is called as physical change.
For example, melting of ice is a physical change as it does not change the chemical composition of ice which was H2O before and after melting only. But the physical state of the substance gets change as it was solid in ice form but converts in to liquid state in the form of water. 
Similarly crumpling a paper sheet, breaking a bottle or moulding of any melted metal are considered as physical changes only because these processes does not involve with any of the change in the chemical composition of the substance. 
Usually physical changes are reversible in nature and turns back to initial state of matter for example we can convert water in to ice again at low temperature. 
The liquid state (water) can again convert in to next state of matter that is gas at high temperature. 
Therefore any of the physical change involves some change in energy level of substance in the form  of heat but the identity of chemical substance remain same as there is no change in the chemical composition of the substance. 
It also form a new substance whose appearance can be different from the initial substance but the chemical composition will be exactly same like after breaking of a glass bottle, the appearance will be change but it will be glass only.    
Unlike physical changes; chemical changes involve change in colour of the substances, change in odour, formation of precipitate or liberation of gaseous products. 
They are generally involved in some energy change by either liberation of heat or absorption of some heat content during the process. 
In any chemical changes, the molecular level of the chemical substance affects and forms a new compound with new set of properties.   
The symbolic representation of a chemical reaction is known as chemical equation. 
A Chemical equation represents that a chemical substance enters in the reaction which is known as reactant and form a new substance which is called as product. 
The chemical equation also denotes the amounts of each substance involved and formed in the chemical reaction. 

Let’s discuss some common examples of chemical reactions which we can easily observe in our everyday life. We all must have witnessed the ‘fizz’ in soft drinks. 
This is due to the presence of Carbonic acid which decomposes in Carbon dioxide and Water. 
Since Carbon dioxide is dissolved in water at high pressure, therefore as we open the bottle, the pressure reduces and gas comes out from the solution. 
For writing the chemical reaction we must know the chemical formula of all the chemical substances which are taking part in the chemical reaction such as in the given example; there are three chemical substances; Carbonic acid (H2CO3), Carbon dioxide (CO2) and Water (H2O). 

The chemical formula of the reactants must be written on the left side of the chemical equation and chemical formula of products must be written on the right side of the table, therefore the chemical equation would be as given below;
H2CO3 →   H2O + CO2 
But this equation does not provide any update about the physical state of the reactants and products of the chemical reaction. 
Hence we must write the descriptions of the state of materials in the reaction in parentheses as subscript after the chemical formula of the chemical substance. 
All the states of matter must be written as abbreviations such as for gas we must write (g), for solid it will be (s), for liquid (l) and for aqueous solution it will be (aq). 
Hence the same reaction can be written as given below;

                          H2CO3 (aq) →   H2O(l) + CO2(g)

Now for the presence of gaseous product we could use an upward pointing arrow (↑) and for a solid precipitate, we could use a downward pointing arrow (↓). 
Since in the given reaction, only carbon dioxide exists in gaseous state, therefore one upward arrow will come after the chemical formula of it as given below;
       (Carbonic acid) H2CO3(aq)  →   (Water) H2O(l) + (Carbon dioxide) CO2(g)(↑)
Remember, that all the chemical compounds have a certain chemical formula which cannot be altered under any circumstances and all these follow the Law of Conservation of Matter
According to this law, there will be no mass loss during any of the chemical reaction. 
There are different types of arrows which can be used to show the direction of various types of reactions such as “→" arrow is used to denote a net forward reaction, and "⇔"indicates a reversible reaction. 
This symbol is used to denote the equilibrium state of the reversible reaction. 
A complete chemical equation also shows the energy change during the reaction with the help of delta, (Δ) sign on the product side. 

For example; in an exothermic reaction some energy evolved during reaction therefore it will come on the product side while in an endothermic reaction some heat requires to initiate the reaction, hence the sign will come on the reactant side.  
The sign of hν indicates the presence of light during photochemical reactions. 
As discussed all the chemical reactions are based on the law of mass conservation which states that the total mass of reactants would be equal to the mass of products formed during chemical reaction. 

We can observe that the total number of any of the atom on both sides of the chemical reaction would be exactly same. 
If it is not so, we should balance it in such a way that all the atoms remain same on both side of the arrow of the chemical reaction.
Let’s discuss one of the chemical reactions between aluminium hydroxide and sulphuric acid to form aluminium sulphate and water. 
We have to start with the chemical formulas of the all the chemical substances involve in the reaction that is Al(OH)3 for Aluminium Hydroxide, H2SO4 for sulphuric acid, Al2(SO4)3 for aluminium sulphate and H2O for water. 
Now write the chemical equation is such a way those reactants must come on left side and product must come on right side of the reaction.
Al(OH)3  +  H2SO4   →   Al2(SO4)3 +  H2O 
Let’s count the number of atoms on both sides of the chemical equation;

Left side          Right side
1 atom Al         2 atoms Al
7 atoms O         13 atoms O
5 atoms H         2 atoms H
1 atom S          3 atoms S

We can observe here sulphate ion is a polyatomic ion which can count as single unit on both side of the reaction. So we can say that;
Left side          Right side
1 atom Al          2 atoms Al
3 atoms O         1 atoms O
5 atoms H         2 atoms H
1 SO42- ion          3 SO42- ion
Let’s start with the balancing of Al atom on both side of the chemical equation by adding 2 in front of Al(OH)3  on reactant side and chemical equation would be;
                 2 Al(OH)3  +  H2SO4  →   Al2(SO4)3  +  H2O
For the balancing of sulphate ion, we can add 3 in front of sulphuric acid on reactant side and the chemical equation would be;
2 Al(OH)3  +  3 H2SO4  →  Al2(SO4)3  +  H2O 
Now, only the O atoms and H atoms remain unbalanced as there are six atoms of O and 12 atoms of hydrogen on the left hand side of the equation. 
But there is only 1 atom O and 2 atoms H on the right side.  So for balancing O and H atoms in the chemical equation, we can add 6 in front of the H2O molecule; 
2 Al(OH)3  +  3 H2SO4  →   Al2(SO4)3  +  6 H2O 
At the end of balancing all the atoms, recheck all the atoms on both side of the chemical equation.