Which is an example of an endothermic process?

• A. Combustion of methane
• B. Photosynthesis
• C. Freezing of water
• D. Condensation of steam

Answer: (B)

Endothermic processes absorb energy from their surroundings. Photosynthesis fits this because plants take in light energy and use it to drive chemical changes that store energy in glucose. The energy input comes from light, not from heat released by the system. By comparison, combustion of methane releases heat (exothermic), freezing of water releases latent heat as it becomes a solid (exothermic), and condensation of steam releases heat as it becomes liquid (exothermic). So photosynthesis is the example of an endothermic process.