Changes Around Us Test - 3

Milk converted to curd, mango converted to mango pickle, and animal waste converted to manure are examples of the changes which cannot be reversed.
Inter-conversion of states of water, e.g., steam to ice, can easily be reversed by changing the temperature and pressure conditions.

Oxidation can be defined as addition of oxygen or removal of hydrogen or loss of electrons.
Whereas, reduction can be defined as addition of hydrogen or removal of oxygen or gain of electrons.

Sublimation is a process by which a solid on heating converts to vapour without going into the liquid state.
This is a physical change.

Potato chips, vegetable oil and fried sandwiches become rancid due to oxidation of fatty acids present in them, but orange does not become rancid as it does not contain fatty acids.

The characteristic feature of an oxidising agent is that it always gains electrons in a redox reaction and gets reduced.

When a small amount of manganese dioxide is added to hydrogen peroxide, oxygen is evolved. This is an example of a decomposition reaction.
H₂O₂ decomposes to H₂O and O₂; MnO₂ acts a catalyst in the reaction.

In the reaction: Zn + H₂SO₄ → ZnSO₄ + H₂, zinc undergoes oxidation because its oxidation state increases from 0 to +2.

In a balanced chemical equation, the number of atoms of different elements on both sides of the equation is always equal.
In equation (4), the number of atoms (H and O) is equal on both the sides of the equation. Thus, equation (4) is a balanced chemical equation.

In a chemical reaction, the reactants come into contact with each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to form the products.