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Answer: Option (B) is the correct answer.
Explanation:
Degree of randomness of the molecules of a substance is known as entropy. More is the kinetic energy between the molecules of a substance more will be the degree of randomness.
Therefore, when a substance is present in a gaseous state then it has the maximum entropy. In liquid state, molecules are closer to each other so, there is less randomness between them.
On the other hand, in solid state molecules are much more closer to each other as they arr held by strong intermolecular forces of attraction. Therefore, they have very less entropy.
- When liquid water is formed from gaseous hydrogen and oxygen molecules then gas is changing into liquid. So, there is decrease in entropy.
- When
decomposes then the reaction will be as follows.
Since, 1 mole is producing 2 moles. This means that degree of randomness is increasing as both the molecules are present in gaseous form.
- In formation of a precipitate, aqueous solution is changing into solid state. Hence, degree of randomness is decreasing.
- Rusting of iron also leads to the formation of solid as it forms
.
Thus, we can conclude that decomposition of gas to
gas is the process that is expected to have an increase in entropy.
A reaction is exothermic if Δ<em>H</em> (or in some textbooks) is negative:
- H₂ + Br → 2 HBr, ΔH < 0.
- CH₄ + 2 O₂ → CO₂ + 2 H₂O, ΔH < 0.
A reaction is endothermic if Δ<em>H</em> is positive:
- 2 NH₃ → N₂ + 3 H₂, ΔH > 0.
- 2 HCl → H₂ + Cl₂ ΔH > 0.
The enthalpy of a system is the sum of its internal energy. ΔH < 0 indicates that the reactants lose internal energy in the reaction. Energy conserves, and those internal energies must have converted to some other form of energy. They typically end up as thermal energy. The reaction will release heat since it is exothermic.
Similarly, ΔH > 0 indicates that the reactants gains internal energy in the reaction. Energy conserves. As a result, the reaction must have gained energy from its surroundings. The reaction will be endothermic since it absorbs heat.