Examkin

Question

Difficulty: MediumExothermic and Endothermic Reactions

Match each chemical transformation or physical process on the left with its correct thermodynamic energy classification and enthalpy description on the right.

  • Dissolution of concentrated sulfuric acid (H2SO4\text{H}_2\text{SO}_4) in waterExothermic process, ΔH<0\Delta H < 0 (Heat is evolved to the surroundings)
  • Thermal decomposition of calcium carbonate (CaCO3\text{CaCO}_3)Endothermic process, ΔH>0\Delta H > 0 (Thermal energy is continuously absorbed)
  • Photosynthesis in green plantsEndothermic process, ΔH>0\Delta H > 0 (Light energy is absorbed to form chemical bonds)
  • Complete combustion of ethanol (C2H5OH\text{C}_2\text{H}_5\text{OH})Exothermic process, ΔH<0\Delta H < 0 (Energy released in product bond formation exceeds energy absorbed in reactant bond breaking)

Answer

Sulfuric acid dissolution matches Exothermic with heat evolved; Calcium carbonate thermal decomposition matches Endothermic with thermal energy absorbed; Photosynthesis matches Endothermic with light energy absorbed; Ethanol combustion matches Exothermic with product bond formation releasing excess energy.
Each process is correctly linked to its thermodynamic behavior: acid dissolution and ethanol combustion release heat to surroundings (exothermic), while carbonate thermal decomposition and photosynthesis require net absorption of external energy (endothermic).

Step-by-Step Solution

1
Classify processes that release heat to the environment
The dissolution of concentrated acid and the combustion of ethanol raise the temperature of their surroundings, identifying them as exothermic reactions with negative enthalpy changes (ΔH<0\Delta H < 0).
Exothermic changes transfer thermal energy outward from the system.
2
Classify processes that require continuous energy absorption
The thermal breakdown of limestone and photosynthesis take in thermal or radiant energy from the outside, classifying them as endothermic reactions with positive enthalpy changes (ΔH>0\Delta H > 0).
Endothermic processes require net energy input to proceed.

Key Concept

Distinction between exothermic (ΔH<0\Delta H < 0, energy released) and endothermic (ΔH>0\Delta H > 0, energy absorbed) processes in physical and chemical systems.
Estimated Time:1m 30s
Rate this question

Topics

Exothermic and Endothermic Reactions