Saturday, 18 March 2017

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Physical and chemical change; differences and definitions

All explanations are put in the simplest and easiest ways possible for fast comprehension. Enjoy.

 Physical changes:

These are the changes which can be easily reversed and no new substances are formed after the process. Examples are:
1) The solution of table salt in water
2) A change in the state of matter
3) Melting of ice
4) Liquefaction of gases
5) Shredded paper etc.

Separation of mixture: evaporation distillation fractional distillation sublimation etc.   

The separation process includes all physical processes such as freezing condensation vaporisation etc.    

READ MORE: the different types of separation techniques
 Learn all about mixtures

Chemical change

 Chemical changes are changes which cannot be easily reversed to its original state and new substances are formed.
Examples are:  
1) Burning of candle
2) The solution of metals and limestone in acids
3) Slacking of lime
4) Electrochemical process
5) Cracking of petroleum
6) Fermentation and decay of substances  etc.

READ MORE: all about compounds 

Differences between physical and chemical changes  

Physical change                               chemical change
a)   it can be easily reversed             it   cannot be easily reversed
b)   no new substances are formed   a new substance is   formed
c)   it liberates little or no energy     it   liberates a lot of heat energy
d)   it cannot be represented            it can be represented   by a   by any chemical equation.
  chemical equation

Experiment shows that zinc oxide a physical change

Aim:  To show that zinc oxide undergoes a physical change.

Method:   Heat zinc oxide in a boiling tube then remove tube from the flame and cool it.

Observation:  While zinc oxide turns yellow on heating it regains its original colour on cooling (white colour).

Conclusion:  The change in colour is a physical change because it is easily reversible without affecting the chemical nature of it.  

 Experiment two: chemical changes

Aim:  To show that chemical changes takes place   a)When a metallic zinc is added to dilute hydrogen sulphate H2SO4.  b) When  (CUCO3)

 Method:  a) Add a plate of metallic zinc to some dilute hydrogen sulphate H2SO4 in a boiling tube when the reaction is completed the solution is evaporated to dryness.
 b) Add some amounts of (CUCO3) in a boiling tube and hold it firmly with a holder in a flame record your observations after a few minutes.

 a) Gas bubbles (hydrogen) are released as zinc gradually dissolves in the acid on complete evaporation a white recipe of ZnSO4 is left behind.
b) Gas bubbles (carbon (iv) oxide CO2) are released on cooling a black recipe of copper (ii) oxides left behind.

 Conclusion  New substances are formed when zinc is added to dilute hydrogen sulphate (H2SO4) and  (CUCO3) is heating.


We witness several physical and chemical changes in our everyday lives and most industries around us from the rubber plastic brewery polymer industries to mere freezing your bottled water in a refrigerator.  Reactions such as: Fermentation process which can be represented by several chemical equations and cannot by reversed is called a chemical change.  2C6H6O6 --- 2C2H5OH + 2CO2  Physical changes on the other hand is used to separate mixture into their component compound while for a chemical change an entirely new product is formed.  If you liked this article kindly share this if you have any additions or suggestions comment below.   Science


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