What is the likely sign of ΔH and ΔS for a combustion reaction?

In the context of combustion reactions, the sign of ΔH (enthalpy change) and ΔS (entropy change) can be understood based on the nature of the reaction. Combustion reactions typically release energy, indicating that they are exothermic processes. Therefore, the enthalpy change, ΔH, is negative. This is because the products of combustion (like carbon dioxide and water, from burning hydrocarbons) are at a lower energy state compared to the reactants, leading to the release of heat.

Regarding the sign of ΔS, combustion reactions usually result in an increase in the number of gas molecules due to the conversion of solid or liquid reactants into gaseous products. This increase in the number of particles in a gaseous state generally correlates with an increase in disorder or randomness in the system, which means that ΔS is likely to be positive. Thus, in a combustion reaction, ΔH is negative due to the release of heat, and ΔS is positive due to the increase in entropy associated with the formation of gaseous products.