Which reaction shows that the enthalpy of formation of h2s is hf = -20.6 kj/mol? a. h2(g) + s(s)  h2s + 20.6 kj
b. h2(g) + s(s) + 20.6 kj  h2s
c.2h(g) + s(s) + 20.6 kj  h2s
d. h2(g) + s(s)  h2s - 20.6 kj

H₂(g) + S(s) → H₂S + 20.6 KJ

Explanation:

The energy changes occur during the bonds formation and bonds breaking.

There ere two types of reaction endothermic and exothermic reaction.

Endothermic reactions:

In this type of reaction energy needed to break the bond are higher than the energy released during bond formation.

For example:

C + H₂O   →  CO  + H₂

ΔH = +131 kj/mol

it can be written as,

C +  H₂O  + 131 kj/mol  →  CO  + H₂

Exothermic reaction:

In this type of reaction energy needed to break the bonds are less than the energy released during the bond formation.

For example:

Chemical equation:

C + O₂   →  CO₂

ΔH = -393 Kj/mol

it can be written as,

C + O₂   →  CO₂ + 393 Kj/mol

The formation of hydrogen sulfide is exothermic reaction.

H₂(g) + S(s) → H₂S       ΔH =  -20.6 KJ

It will be written as,

H₂(g) + S(s) → H₂S + 20.6 KJ

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