Question

Define:
a) Chemical combination reaction
b) Endothermic reaction
c) Oxidation reaction

Answer 1

Hint: All these reactions are a type of redox reactions where reduction and oxidation takes place at the same time. In oxidation there is loss of electrons and in reduction gain of electrons takes place.

Complete answer:
> Chemical combination reaction: A chemical reaction in which two or more elements or compounds combine together to form a single chemical compound are known as combination reactions.
For this reaction to be a redox either one of the two chemical compounds must be in elemental form that is pure state. For example:
$\;C\;+\;O_2\;\to\;CO_2$
In this reaction carbon and oxygen combine together to form a single compound.
> Endothermic reaction: In this reaction heat is absorbed by the system. It is a process with an increase in the enthalpy H of the system. In such a process system usually absorbs thermal energy from its surroundings.
For example: Melting of ice is an endothermic reaction. The heat given to the system is absorbed by it and ice starts melting.
> Oxidation reaction: it is a reaction in which an atom or ion loses one or more electrons which is why it is also called a de-electronation reaction. This reaction also involves addition of oxygen or any other electronegative element, or as a process which involves the removal of hydrogen or any other electropositive element. For ex:
$Mg(s) + C{l_2}(g) \to MgC{l_{2(s)}} \\
Na \to N{a^ + } + {e^ - } \\ $
In the first reaction Cl an electronegative element is added and the second reaction shows loss of electrons result in positive charge.

Note: A reaction can carry a lot of processes during its occurrence, that is combustion reaction could be an oxidation reaction as well. An oxidizing agent or oxidant is a substance that supplies oxygen or any other electronegative element and removes hydrogen or any electropositive element. An oxidizing agent after carrying out oxidation is itself reduced in the reaction.