Question

Potential energy diagram for the reaction

"A graph of time versus potential energy labeled upper H upper C l plus upper N a upper O upper H right arrow upper N a upper C l plus upper H subscript 2 upper O plus 58 kilojoules. The graph has Time on the horizontal axis and potential energy on the vertical axis. A line starts high and runs briefly parallel to the horizontal axis; this segment is labeled upper H upper C l plus upper N a upper O upper H. It the curves up slightly, peaks, and curves down sharply to run near and parallel to the horizontal axis; this section is upper N a upper C l plus upper H subscript 2 upper O.

exothermic

endothermic

Answer 1

This reaction is exothermic.

Why:
- The products (NaCl + H2O) are at lower potential energy than the reactants (HCl + NaOH), so energy is released as the reaction proceeds.
- The diagram shows “+58 kJ” released; using the usual sign convention ΔH = H_products − H_reactants = −58 kJ (the system loses 58 kJ), so heat is given off to the surroundings.

Other useful labels from the diagram:
- Activation energy (forward, Ea,f): the energy difference between the reactants and the peak.
- Activation energy (reverse, Ea,r): the energy difference between the products and the peak. Numerically Ea,r = Ea,f + 58 kJ.