Question

Select the correct statement about enthalpy
• Enthalpy is a state function
• For a reaction carried out at constant pressure, the heat absorbed or released is equal to the enthalpy change
• The enthalpy change of a reaction depends on the path followed by the reaction
• Breaking chemical bonds always requires absorption of energy Choose the correct answer from the options given below:
• B, C & D Only
• A, B & D Only
• A & B Only
• A, C & D Only

• A. B, C & D Only
• B. A, B & D Only
• C. A & B Only
• D. A, C & D Only

Hint:

Remember:
• Enthalpy is a state function.
• At constant pressure: \[ \Delta H = q_p \]
• Bond breaking absorbs energy.
• Bond formation releases energy.

Answer 1

The Correct Option is B

Concept: Enthalpy is an important thermodynamic property represented by: \[ H \] It is defined as: :contentReference[oaicite:0]{index=0} where:
• \(H\) = enthalpy
• \(U\) = internal energy
• \(P\) = pressure
• \(V\) = volume Enthalpy helps us understand:
• Heat absorbed
• Heat released
• Energy changes during chemical reactions

Step 1: Examine Statement A carefully. Statement A says: “Enthalpy is a state function.” This statement is correct. A state function depends only upon:
• Initial state
• Final state It does not depend upon the path followed. Since enthalpy depends only on the thermodynamic state of the system: \[ \boxed{ \text{Enthalpy is a state function} } \] Hence Statement A is correct.

Step 2: Examine Statement B carefully. Statement B says: “For a reaction carried out at constant pressure, the heat absorbed or released is equal to the enthalpy change.” This statement is also correct. At constant pressure: :contentReference[oaicite:1]{index=1} where:
• \( \Delta H \) = enthalpy change
• \( q_p \) = heat exchanged at constant pressure Thus:
• Heat absorbed \( \Rightarrow \Delta H > 0 \)
• Heat released \( \Rightarrow \Delta H < 0 \) Therefore Statement B is correct.

Step 3: Examine Statement C carefully. Statement C says: “The enthalpy change of a reaction depends on the path followed by the reaction.” This statement is incorrect. Since enthalpy is a state function: \[ \boxed{ \Delta H \text{ depends only on initial and final states} } \] It is independent of the reaction path. Whether the reaction occurs:
• In one step
• In several intermediate steps the total enthalpy change remains the same. This is the basis of Hess's law. Hence Statement C is false.

Step 4: Examine Statement D carefully. Statement D says: “Breaking chemical bonds always requires absorption of energy.” This statement is correct. To separate bonded atoms:
• Attractive forces must be overcome.
• External energy must be supplied. Thus bond breaking is always: \[ \boxed{ \text{Endothermic} } \] whereas bond formation releases energy. Hence Statement D is correct.

Step 5: Identify correct statements. We observed:
• A is correct
• B is correct
• C is incorrect
• D is correct Therefore: \[ \boxed{ A,\ B\ \&\ D\ \text{Only} } \]

Step 6: Match with the options. This corresponds to: \[ \boxed{(2)} \] Additional Understanding: Important thermodynamic ideas:
• Bond breaking absorbs energy.
• Bond formation releases energy.
• Enthalpy change determines whether reaction is exothermic or endothermic. Final Conclusion: Correct statements are: \[ \boxed{ A,\ B\ \&\ D\ \text{Only} } \] Hence, the correct answer is: \[ \boxed{(2)} \]