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GATE 2026 CH – Question 27

Process Calculations · Steady and unsteady state mass and energy balances · 1 mark · Multiple select

Which of the following statements regarding the heat of reaction is/are CORRECT?

  1. For endothermic reaction, it is positive.
  2. For exothermic reaction, it is negative.
  3. For exothermic reaction, it is positive.
  4. It is the enthalpy change for a process in which stoichiometric quantities of reactants, at a temperature and pressure, react completely in a single reaction to form products at the same temperature and pressure.

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Correct answer: (A) For endothermic reaction, it is positive.; (B) For exothermic reaction, it is negative.; (D) It is the enthalpy change for a process in which stoichiometric quantities of reactants, at a temperature and pressure, react completely in a single reaction to form products at the same temperature and pressure.

Explanation

By the usual sign convention the heat of reaction is $\Delta H_r = H_{products} - H_{reactants}$. It is positive for an endothermic reaction (heat is absorbed) and negative for an exothermic one (heat is released). Statement D is the standard definition. Statement C contradicts the sign convention.