Topics in ChemistryPhysical Properties of Matter explained with Examples Chemical Properties of Matter explained with Examples Differences between Physical and Chemical Change Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid State of Matter: Characteristics of Liquids Gaseous State of Matter: Characteristics of Gases Molar Mass, Worked Examples and Differences with Molecular Mass Elements: Characteristics of Elements Salts and Types of Salt in Chemistry Mixtures and Separation of Mixtures Mixtures and Separation of Mixtures - part 2 Mixtures and Separation of Mixtures - part 3 Physical Change and Chemical Change Concept of Ions and Electrolytes Grahams Law of diffusion, Worked Example and Importance Metals - Physical Properties of Metals Daltons Atomic Theory and its Modifications Periodic Table: Classification of Elements in the Periodic Table
Academic Questions in Chemistry
Which of the following is NOT a characteristic of chemical change?
Which of the following statement is FALSE concerning a physical change _____.
The following substances will sublime EXCEPT _____.
Which of the following is a state of matter?
The ideal way of separating a mixture of blood is through _____.
Which of the following separation technique is used to separate an insoluble solid that sediments in a liquid?
A _____ mixture is said to be uniform all through.
The reaction involving an acid and a base is termed _____.
Having a solid understanding of physical and chemical change is one of the ideal knowledge a student who aspire to become excellent in chemistry should gain.
Recall that Chemistry is the study of matter and the changes they undergo.
A physical change is a change that is easily reversible and no new substance is formed.
As an instance; when we add NaCl(sodium chloride or common salt) into H2O (hydrogen oxide or water), a salt solution will be formed.
This change that resulted from the mixture of salt and water is a physical change because we could easily separate the salt solution to get back its constituents, (that is, common salt and water).
Note: Since no new substance is formed in the mixture of NaCl and H2O, the best name we could attribute to such mixture is a salt solution.
Salt solution does not have any ideal chemical formula. In short, a mixture have no ideal chemical formula because it is associated with a physical change.
This salt solution in our instance above can be separated by a technique called evaporation.
A mixture of NaCl and H2O does not have a chemical name because a new substance is NOT formed.
Another example of a physical change is a mixture of red oil and water. There is no chemical name that can be attributed to this mixture since no new substance is formed.
Red oil and water are two immiscible liquid and as result, their mixture can be separated via the separating funnel technique.
In a separating funnel technique, the water (at the bottom of the mixture) is first tapped out, leaving behind the oil.
Recall that water has a higher density than oil. For this reason, it remains at the bottom while the oil (with lower density) floats on it.
A third example of a physical change is the mixture of sand and water. Since no new substance is formed, no name can be ascribed to such mixture. (The best we can name it is a mixture of sand and water)
Decantation is the technique used for separating water from sand, (that is, an insoluble solid in a liquid).
Note: The freezing of liquid water into ice is also a physical change since it can be easily reversible.
Moreover, the chemical formula of water and ice remains the same (H2O) thus, no new substance is formed.
Having a good understand of physical change will give you a clue on what a chemical change is.
A chemical change is a change that is NOT easily reversible and a new substance is formed.
Take for instance, if we exposed a piece of iron (Fe) to the atmosphere and rainfall (or water) for some period of time; we will observe that the iron will gradually begin to rust until it finally erodes away. When this happens, we no longer have our iron (Fe) and unfortunately, there’s no way to recover it.
What we have now is referred to as rust and the process leading to the formation of rust is referred to as corrosion.
On the other hand, the rust formed from the exposed iron is an entirely new substance and it has a chemical name called iron (III) oxide or ferric oxide or hematite with a chemical formula Fe2O3.
We cannot reverse the formed rust (Fe2O3) into iron (Fe).
This irreversibility of the new substance formed is the main idea behind a chemical change.
Another example of a chemical change is the formation of water (H2O).
The constituent elements in the formation of H2O are hydrogen molecule (H2) and oxygen molecule (O2).
The reaction is shown below:
2H2(g) + O2(g) -> 2H2O(l)
From the above equation, a new substance has been formed and that’s water (H2O).
Water is completely different from hydrogen and similarly, so is it completely different from oxygen. As a matter of fact, water cannot be reversed to its constituent elements which are hydrogen and oxygen respectively.
The new substance formed from the reaction between hydrogen and oxygen has a chemical name and that’s hydrogen oxide or water; with a chemical formula (H2O).
Note: Other examples of chemical changes seen around us include:
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Amazing facts in Chemistry
The only letters that failed to appear on the periodic table are letters:
Gold and copper are the only two non-silvery colored metals. Please read some interesting facts about gold here
Copper is the only metal that is naturally antibacterial. This is why you would see some children carry copper water bottles to school
Water actually freezes faster when it’s warm than when it’s cold
Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy.
Please read on modification of Dalton's atomic theory here.
If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.
Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre
NOTABLE POINTS IN Chemistry