Question

Which of the following equations is used to obtain enthalpy change of a reaction?

• A. \(\Delta H = \sum \Delta H_P-\sum \Delta H_R\)
• B. \(\Delta H = \sum \Delta H_R-\sum \Delta H_P\)
• C. \(\Delta H = \sum \Delta H_P+\sum \Delta H_R\)
• D. \(\Delta H = \frac{\sum \Delta H_P}{\sum \Delta H_R}\)

Hint:

Enthalpy change is products minus reactants.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
Enthalpy is a state function, so the change for a reaction depends only on the initial (reactants) and final (products) states.

Step 2: Detailed Explanation
Change = final minus initial:
\[ \Delta H = \sum \Delta H_P - \sum \Delta H_R \]
A positive value means heat is absorbed, and a negative value means heat is released. Option (B) reverses the sign, (C) adds the terms, and (D) divides them, which has no physical meaning.

Final Answer:
The correct relation is products minus reactants, option (A). \[ \boxed{\Delta H=\sum\Delta H_P-\sum\Delta H_R\ \text{(A)}} \]