Chemical And Physical Changes

Chemical and Physical Changes

Changes in Chemistry

Types Of Changes

In chemistry, not all changes produce new chemicals. This simply means there two types of changes: physical and chemical changes

Physical Changes

Physical Change: A physical change is the changes that can be easily reversed and no new substances are formed.
Matter can exist in three physical forms:
SOLID, LIQUID AND GAS

Changes In Matter

Matter can be changed from one state or form to another.
For example ;water is an example of a substance that undergoes a change of state.
SOLID-LIQUID-GAS. by application of heat

From ICE 0°C to WATER 100°C to STEAM(water vapor),

it can also reversed from steam(gas) to liquid(water) and from liquid to solid

Liquid to solid is called freezing while gases to liquid is called condensation

The example above is the melting of a solid to liquid, the freezing of liquid to solid, the vapourizing of a liquid to gases and the condensing of gases to liquid.top↑

2) Another example of physical change is the dissolution of sodium chloride(common salt) in water. It form a colouress solution and the salt can be removed by evaporating the solution to dryness and the residue as the pure salt.

3) Another example of physical change is the magnetization of iron nail by a strong magnet. After the nail as becomes a magnet, it can be used to pick up a pin but still weighs the same as before.

Chemical Changes

A chemical change is the changes that cannot be easily reversed and in which a new substances are formed.

There are many examples of chemical changes
E.g
a) reaction of some metals with dilute acid e.g reaction of zinc metal with dilute HCL
Zn(s) +2HCL(aq) – ZNCL2(s) + H2(g)

b) iron nail in a solution of CUSO4(aq) for a short time.
There will be a displacement reaction; iron nail will be coated with a layer of redbrown copper .
Fe(s) + CUSO4(aq) – FeSO4(aq) + CU(s)

c) burning of magnesium ribbon in a bunsen burner. It burns with a bright white light and forms a white powder of magnesium oxide.top↑
2Mg(s) + O2(g) – 2MgO(s)

d) reaction of metals. E.g calcium reacts with water to produce hydrogen gas.
Ca(s) + 2H2O(l) – Ca(OH)2(aq) + H2

NOTE :In all the reactions above it would be difficult to reverse the changes and get the original substances.

Differences Between Physical Changes And Chemical Changes.

1) Physical changes reaction are easily reversible while chemical changes reactions are mostly difficult to reverse.

2) In physical changes no new substances are formed while in chemical changes new substances are formed.

3) In physical changes very little amount of heat is absorbed or emitted while in chemical changes remarkable large amount of heat are emitted or absorbed.top↑

4) In physical changes there is no change in mass, that is, the mass of the reactant before reaction is the same thing as the mass of the product after reaction while in chemical changes there is new mass due to the new substances formed, that is, reactant mass before reaction is not the same thing as the mass of the product after reaction.

5) And also chemical reaction is more useful than physical reaction, chemical products are use extensively than physical product.

Let stop here for todayour next topic will be on element, mixture and compoundtop↑

Next Topic :Element, Mixture And Compound


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