What does ΔH represent in a chemical reaction?

What does ΔH represent in a chemical reaction?

• A. The energy change from products to reactants
• B. The activation energy of the reaction
• C. The rate constant of the reaction
• D. The energy change from reactants to products

Answer: (C)

ΔH represents the enthalpy change of a reaction. It is the difference in enthalpy between products and reactants, H_products minus H_reactants, and it corresponds to the heat absorbed or released by the system at constant pressure. A positive ΔH means the reaction is endothermic (absorbs heat); a negative ΔH means it is exothermic (releases heat). This is distinct from the activation energy, which is the energy barrier to reach the transition state, and from the rate constant, which describes how fast the reaction proceeds. So, ΔH captures the energy change from reactants to products.

ΔH represents the enthalpy change of a reaction. It is the difference in enthalpy between products and reactants, H_products minus H_reactants, and it corresponds to the heat absorbed or released by the system at constant pressure. A positive ΔH means the reaction is endothermic (absorbs heat); a negative ΔH means it is exothermic (releases heat). This is distinct from the activation energy, which is the energy barrier to reach the transition state, and from the rate constant, which describes how fast the reaction proceeds. So, ΔH captures the energy change from reactants to products.