If delta H is negative, what type of reaction has taken place?

When delta H is negative, it indicates that heat is being released during the reaction. This characteristic is associated with exothermic reactions, where the energy of the products is lower than the energy of the reactants. In an exothermic process, the system loses energy to the surroundings in the form of heat, resulting in an increase in the temperature of the surroundings.

Understanding the implications of a negative delta H is crucial for interpreting energy changes during chemical reactions. Exothermic reactions are often spontaneous and can be identified in processes like combustion, where fuels react with oxygen to produce heat, light, and often products like carbon dioxide and water. While combustion is a specific type of exothermic reaction, it does not encompass all exothermic reactions. Therefore, while the answer connects well to the definition of an exothermic reaction, it's necessary to remember that not all exothermic reactions are classified as combustion.