Question

which reaction is endothermic?
hcl + naoh → nacl + h₂o + 58 kj
6co₂ + 12h₂o + energy → c₆h₁₂o₆ + 6o₂ + 6h₂o
2na + cl₂ → 2nacl + energy
2c₂h₆ + 7o₂ → 4co₂ + 6h₂o + 2,502 kj

Explanation:

An endothermic reaction absorbs energy (energy is a reactant), while exothermic releases energy (energy is a product).

• First option: Energy (58 kJ) is a product → exothermic.
• Second option: Energy is a reactant → endothermic (photosynthesis, absorbs energy).
• Third option: Energy is a product → exothermic (synthesis of NaCl, releases energy).
• Fourth option: Energy (2,502 kJ) is a product → exothermic (combustion of ethane, releases energy).

Answer:

B. \( 6\ce{CO_2} + 12\ce{H_2O} + \text{energy}
ightarrow \ce{C_6H_{12}O_6} + 6\ce{O_2} + 6\ce{H_2O} \)