Which of the following reactions are exothermic?

 

$$\begin{gathered} 1) C + O2 → CO2 \\ 2) 2Mg + O2 → 2MgO \\ 3) CuSO4 + 5H2O → CuSO4.5H2O \\ 4) All the above \end{gathered}$$

An Element is a pure substance of one type of atom. In chemistry, any material such as carbon, hydrogen, iron, or oxygen that cannot be broken down into more fundamental substances is nothing but an element.

A pure substance can be defined as any single type of material that has not been contaminated by another substance. In chemistry, a pure substance has a definite composition. It can be a compound or an element. A pure substance is considered to be a material that consists of one type of "building block" of matter.

Examples of pure substances include tin, sulfur, diamond, water, pure sugar (sucrose), table salt (sodium chloride) and baking soda (sodium bicarbonate).

Tin, sulfur, and diamond are examples of pure substances which are chemical elements. All elements are pure substances.

Water, sugar, salt and baking soda are pure substances which are chemical compounds. Chemical compounds also are pure substances

The s,p,d,f configuration for cobalt (Co) is 1s22s22p63s23p64s23d7, determined by the position of the element on the periodic table. The electron configuration for Cobalt at ground state would simply be Co: [Ar] 4s²3d⁷.

The electron configuration of Cobalt will end in d block as Cobalt is an inner transition metal. Cobalt is in the 7th column of the d block and therefore has 7 d electrons d7.

Bond Order  = 1/2[ Nb - Na]

where

Nb = Number of electrons in bonding molecular orbitals.

Na = Number of Electrons in antibonding molecular orbitals

Bond Order of N2⁺:

Total number of electrons: 13

Electronic Configuration= :σ1s² σ*1s² σ2s² σ*2s² π 2py² [π2pz² σ2px1 ]

Bond Order = [9-4]/2 = 5/2 = 2.5.

The seven elements — helium, neon, argon, krypton, xenon, radon, and oganesson of Group 18 of the periodic table are Noble or Inert gases.

Radon is the heaviest and Helium is the lightest gases of the noble gases.

The molar mass of H2O can be calculated as the following.

M(H2O)= [2 x M(H)] + [M(O)].

And we know that M(H) = 1g/mol, M(O) = 16g/mol.

So, M(H2O)= 2x1 + 16 = 18g/mol,

That means 1 mole of H2O contains 18g.

Hence, one mole of H2O corresponds to 18 grams.

An atom is the smallest particle of a substance. Chemical substances are divided into two major groups. They are

1. Pure Substances (and)

2. Mixtures.

There are two types of pure substances that are Elements and Compounds.

Elements : An element is a substance that is made up of only one kind of atoms and cannot be broken down into simpler substances by chemical means. Metals and Non- metals come under elements.

Examples of elements are Iron, Silver, Gold, Mercury etc.

Compounds : A Compound is a substance that is formed when two or more elements combine chemically.

Examples of compounds are Water, Carbon dioxide, methane, vinegar etc.

Mixtures : A Mixture is formed when two or more substances mixed together but not chemically combined.

Example: Air.

No. Boiling water is not a chemical change. Because in this process it doesn't loss its properties. It just changes its state i.e, from liquid state to gaseous.

Hence, Boiling water is a Physiacl change and not a chemical change.