Question

Is Enthalpy Positive Or Negative?

Answer 1

1. The difference(subtract) of," the energy required to break the bonds between the reactants is the enthalpy of a reaction" and “the energy released when new bonds are formed in the products”. Therefore, a reaction is exothermic and its enthalpy will be negative if it releases more energy than it takes in, the reaction is endothermic, and enthalpy will be positive.
2. Consider it as a certain amount of heat being evaporated (or removed) from the reaction.
3. Endothermic reactions have positive enthalpies because they absorb or use more energy than they produce. Let's examine the enthalpy changes that occur during methane burning.
4. The bonds between the oxygens and the carbon as well as the links between the hydrogens are broken in this reaction. These bonds must be broken, which needs energy to be consumed by the reaction.
5. Then, however, new bonds are formed between carbon and oxygen, and between hydrogen. The energy released in this reaction is more than the energy absorbed. This indicates that combustion is an exothermic reaction with a net negative enthalpy.

Hence, enthalpy can either be positive or negative.