A team in which there is chemical change occur in substance. In a chemical reaction, one or more new chemical substance are formed from the original substance. Energy is either absorbed or released during chemical reactions. Chemical reactions occur at different speeds. Some reactions are very fast and some are very slow. As we know that their will be energy released or absorbed during reactions, on this basis reactions are divided into 3 groups
(1)Exothermic reaction: In these reaction heat is released. All combustion reaction are exothermic reaction. For eg.
CH 4 + 2O 2 -> CO 2 2H 2 O + heat
(2) Endothermic reaction: In these reaction energy is absorbed
Eg. N 2+ O 2+ heat -> 2 NO
(3) Photochemical reaction: The reaction which take place only when light is present. Eg. Photosynthesis
Some other type of reaction
Decomposition reaction: The reaction in which substance decompose on heating. eg.
2HgO -> 2 Hg + O 2
Combination or addition reaction: when molecules combine to forms a large molecules
Eg. 2 Mg + O 2 -> 2MgO
Displacement reaction: The reaction in which one element of a compound replace by another one.
Eg. Fe + CuSO 4 -> FeSO 4 + Cu
Disproportional reaction: A chemical reaction In which only one substance vet oxidized as well as reduced is known as disproportional reaction
Eg. P 4 + NaOH + 2H 2 O -> 2 NaH 2 PO 2 + PH 3 here Phosphorus is oxidized as well as reduced.
Double displacement reaction: In a reaction where two compound react to form two different compound by mutual exchange ion. Eg.
AgNO 3 +NaCl -> NaNO 3 + AgCl
Neutralization reaction: A type of double decomposition when an acid reacts with base and form salt and water.
NaOH + HCl -> NaCl + H2
Reversible reaction: A reaction which can occur in both directions
Irreversible reaction: A reaction which cannot occur in both directions.
The number of moles of substance dissolved in litre of the solution
Acid and Bases
Acids : It is a substance which ionized in water to give H + ions. for eg. Hydrochloric acid ionized in water to give H + ions
HCl -> H+ +OH –
Type of Acids
There are two type of acid (1) strong acid (2) weak acid
- Strong acid : An acid which is completely ionized in water and produce a large number of H + ions. Eg. HCl, sulphuric acid etc
- Weak acid: Acid which is partly ionized in water eg. Carbonic acid, acetic acid etc.
Properties of Acid
- It changes the color of blue litmus to red
- It is sour in taste
- It reacts with carbonate to produce carbon dioxide gas
- If react with bases to neutralization.
A base is a substance which react with an acid to form salt. Bases are Proton acceptor. They contain oxide ions or OH - ions. A base is a substance which dissolves in water to give OH – ions
Bases are of two type:
- Strong base: they gives large number of OH – ions. Eg. NaOH, KOH etc.
- Weak base : they gives small number of OH – ions. Eg. CaOH
Properties of bases:
- It changes the color of red litmus to blue.
- It is bitter in taste
- It reacts with acid to neutralization
pH scale is a positive logarithm of Hydrogen ion concentration in moles per litre.
Chemical name of Washing soda is Sodium carbonate with 10moles of wager. It’s chemically formula is Na 2 CO 3 . 10 H 2 O
Uses of washing soda
- It is used as a cleaning agent for domestic purpose.
- Used for softening hard water
- It is used to manufacture of many useful sodium compound like caustic soda, borax, glass ,soap etc.
- Used as laboratory reagents
Its chemical name is Sodium bicarbonate and its chemical formula is NaHCO 3 .
- It is used as antacids in medicine to remove acidity
- It is used to make baking powder
Chemical name of bleaching powder is Calcium Oxychloride and its formula is CaOCl 2
Manufacturing of bleaching powder: It is manufactured by passing chlorine gas over dry slaked lime.
- It is used in textile industry, paper industry etc.
- It is used for bleaching washed cloth.
- It is used for making drinking water free from germs.
- It is used to form chloroform
- It is used as oxidizing agent