### Correct Option: D. absorbed, +ΔH ### Detailed Explanation: 1. **Understanding Endothermic Reactions**: - An endothermic reaction is a type of chemical reaction that absorbs heat from its surroundings. This means that during the reaction, the system takes in energy in the form of heat, which can lead to a decrease in the temperature of the surroundings. 2. **Heat Absorption**: - The term "absorbed" indicates that the reaction requires energy input. This is a key characteristic of endothermic processes. For example, when ammonium nitrate dissolves in water, it absorbs heat, resulting in a cooling effect. 3. **Enthalpy Change (ΔH)**: - The change in enthalpy (ΔH) is a measure of the heat content of a system. In the context of endothermic reactions: - If a reaction absorbs heat, the enthalpy change (ΔH) is positive. This is because the products of the reaction have a higher energy content than the reactants. - The positive sign (+ΔH) indicates that energy is being absorbed from the surroundings. 4. **Why Option D is Correct**: - Option D states that heat is "absorbed" and can be represented by the symbol "+ΔH". This accurately describes the nature of endothermic reactions, where heat is taken in, leading to a positive change in enthalpy. ### Why the Other Options are Incorrect: - **Option A: liberated, -ΔH**: - This option states that heat is "liberated" (released) and represented by "-ΔH". This describes exothermic reactions, where heat is released into the surroundings, not endothermic reactions. Therefore, this option is incorrect. - **Option B: liberated, +ΔH**: - Similar to Option A, this option incorrectly states that heat is "liberated" but uses a positive sign for ΔH. Since liberated heat corresponds to a negative change in enthalpy (exothermic), this option is also incorrect. - **Option C: absorbed, -ΔH**: - This option correctly states that heat is "absorbed", but it incorrectly uses "-ΔH". A negative ΔH indicates that heat is released, which is characteristic of exothermic reactions. Thus, this option is incorrect. ### Summary of Key Points: - An endothermic reaction **absorbs heat** from the surroundings. - The enthalpy change (ΔH) for endothermic reactions is **positive (+ΔH)**. - Endothermic reactions result in a **cooling effect** in the surroundings. - Understanding the signs of ΔH is crucial for distinguishing between endothermic and exothermic reactions. This thorough understanding of endothermic reactions will help you in identifying and classifying various chemical processes in your studies.