Examkin

Question

Difficulty: MediumExothermic and Endothermic Reactions

When solid ammonium chloride (NH4Cl\text{NH}_4\text{Cl}) is dissolved in water inside a beaker, the temperature of the reaction mixture drops noticeably from 27∘C27^\circ\text{C} to 18∘C18^\circ\text{C}. Which of the following statements correctly accounts for the thermochemical behavior of this process?

  1. The process is endothermic because thermal energy is absorbed from the surroundings, resulting in a positive enthalpy change (ΔH>0\Delta H > 0).Answer
  2. B
    The process is exothermic because thermal energy is absorbed from the surroundings, resulting in a negative enthalpy change (ΔH<0\Delta H < 0).
  3. C
    The process is endothermic because thermal energy is released to the surroundings, resulting in a negative enthalpy change (ΔH<0\Delta H < 0).
  4. D
    The process is exothermic because thermal energy is released to the surroundings, resulting in a positive enthalpy change (ΔH>0\Delta H > 0).

Answer

The dissolution process is endothermic because thermal energy is absorbed from the surroundings, resulting in a positive enthalpy change (ΔH>0\Delta H > 0).
The correct option identifies that a observed temperature drop in the surrounding solution signifies heat absorption by the chemical system. By definition, processes absorbing heat from their surroundings are endothermic and have a positive enthalpy change (ΔH>0\Delta H > 0).

Step-by-Step Solution

1
Analyze the temperature change observed during the process.
The temperature of the solution decreased from 27∘C27^\circ\text{C} to 18∘C18^\circ\text{C}, indicating heat was absorbed by the system from the surrounding solution.
When a reaction system absorbs heat from its immediate surroundings, the temperature of the surroundings falls.
2
Classify the type of thermochemical process.
A process that absorbs thermal energy from the surroundings is classified as endothermic.
Endothermic processes require heat input to break solute-solute and solvent-solvent interactions.
3
Determine the sign of the enthalpy change (ΔH\Delta H).
Since Hproducts>HreactantsH_{\text{products}} > H_{\text{reactants}}, ΔH=Hproducts−Hreactants>0\Delta H = H_{\text{products}} - H_{\text{reactants}} > 0 (positive).
In endothermic reactions, the heat content (enthalpy) of the products is greater than that of the reactants.

Key Concept

Endothermic Dissolution and Enthalpy Sign Convention
Estimated Time:1m 0s
Rate this question

Topics

Exothermic and Endothermic Reactions