Which reaction is endothermic?
$HCl + NaOH \rightarrow NaCl + H _2 O +58 kJ$
$6 CO _2+12 H _2 O +$ energy $\rightarrow C _6 H _{12} O _6+6 O _2+6 H _2 O$
$2 Na + Cl _2 \rightarrow 2 NaCl +$ energy
$2 C _2 H _6+7 O _2 \rightarrow 4 CO _2+6 H _2 O +2,502 kJ$
Answer (1)
An endothermic reaction absorbs heat.
The first, third, and fourth reactions release energy (exothermic).
The second reaction absorbs energy.
The endothermic reaction is: 6 C O 2 + 12 H 2 O + energy → C 6 H 12 O 6 + 6 O 2 + 6 H 2 O .
Explanation
Identifying Endothermic Reactions An endothermic reaction is a reaction that absorbs heat from its surroundings. In the given reactions, we need to identify the one where energy is absorbed (i.e., energy is a reactant).
Analyzing Reaction 1 The first reaction, H Cl + N a O H i g h t ha r p oo n u pN a Cl + H 2 O + 58 k J , releases 58 kJ of energy, indicating it is an exothermic reaction.
Analyzing Reaction 2 The second reaction, 6 C O 2 + 12 H 2 O + energy i g h t ha r p oo n u p C 6 H 12 O 6 + 6 O 2 + 6 H 2 O , requires energy as a reactant. This means it absorbs energy and is therefore an endothermic reaction.
Analyzing Reaction 3 The third reaction, 2 N a + C l 2 i g h t ha r p oo n u p 2 N a Cl + energy, releases energy, indicating it is an exothermic reaction.
Analyzing Reaction 4 The fourth reaction, 2 C 2 H 6 + 7 O 2 i g h t ha r p oo n u p 4 C O 2 + 6 H 2 O + 2 , 502 k J , releases 2,502 kJ of energy, indicating it is an exothermic reaction.
Conclusion Therefore, the endothermic reaction is the one where energy is a reactant: 6 C O 2 + 12 H 2 O + energy i g h t ha r p oo n u p C 6 H 12 O 6 + 6 O 2 + 6 H 2 O .
Examples
Endothermic reactions are crucial in cooking. For example, baking a cake requires heat to be absorbed by the ingredients, transforming them into a delicious treat. Similarly, in photosynthesis, plants absorb sunlight (energy) to convert carbon dioxide and water into glucose and oxygen. Understanding endothermic reactions helps us optimize these processes, making cooking more efficient and enabling plants to produce the oxygen we breathe.
