Which of the following reactions are exothermic?

 

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

A) Cooking of Food  ------ Chemical Change

B) Digestion of Food ----- Chemical Change

C) Freezing of water ----- Physical Change

D) Water is heated up ---- Physical Change

because here the chemical composition of the substance changes in A & B only.

Since we know that, If the chemical composition is changing then it is a chemical change and if the chemical composition is remaining the same, then it is a physical change.

Nitrogen is found as a diatomic molecule (N2) in nature. There is a triple bond between the two nitrogen atoms.

The triple bond is pretty strong. Therefore, it needs a lot of energy to break those bonds and participate in a reaction. So nitrogen is commonly referred to as and used as an inert gas (high abundance & low cost.) However, it’s not truly inert like most noble gases. Nitrogen does react if the conditions are met. But those conditions are not exactly mild, but are not as extreme as for noble gases.

It forms nitric oxide and nitrogen dioxide with oxygen, ammonia with hydrogen, and nitrogen sulfide with sulfur.

Milk is not a pure substance since it has so many constituents that can be separated physically.

Compounds are pure substances formed from elements unlike mixtures.

True, Water is a Pure substance and not a mixture.

We know that, A mixture is when two or more substances combine physically together. You can find that the mixture retains the properties of the original components.

In water, two hydrogen atoms combine with one oxygen atom chemically, forming a new substance that has properties different from hydrogen alone or oxygen alone.

Therefore, water is not a mixture; it is a compound and it is pure.

All the given reactions are Decomposition reactions.

Decomposition reaction is a reaction in which only one reactant is splitted into two or more products.

The given compund Li3PO4 name is Lithium phosphate.

Lithium phosphate is a white crystal at room temperature. It is slightly soluble in water.

It  can be used to produce glass, disk, colorful phosphor powder. It can also be used as a catalyst in some reactions.

We will rewrite the formula as an equation.

2K + 2Cr + 7O = 0

The zero comes from there being no overall charge on the compound.

Each oxidation number is represented by the element's symbol.

Since this compound is not a peroxide or superoxide, the oxidation value for O is -2

K being in group 1 has a +1 charge and therefore has an oxidation number of K is +1

Now, by putting known values in we have:

2(+1) + 2(Cr) + 7(-2) = 0

2 + 2Cr -14 = 0

2Cr = +12

Cr = +6.

In common we all call the systematic name of NH4ClO3 as Ammonium Chlorate. But originally the systematic name is azanium trioxidochlorate.