Determine whether each process is exothermic or endothermic and indicate the sign of ΔH. a. dry ice evaporating b. a sparkler burning c. the reaction that occurs in a chemical cold pack used to ice athletic injuries

Key Concepts

Exothermic and Endothermic Processes

Exothermic processes release energy, usually in the form of heat, to the surroundings, resulting in a negative change in enthalpy (ΔH < 0). In contrast, endothermic processes absorb energy from the surroundings, leading to a positive change in enthalpy (ΔH > 0). Understanding these definitions is crucial for determining the nature of the processes described in the question.

Phase Changes

Phase changes, such as evaporation or sublimation, involve the transition of a substance from one state of matter to another. For example, dry ice (solid CO2) sublimates directly to gas, which is an endothermic process as it requires energy input to overcome intermolecular forces. Recognizing the energy dynamics during phase changes helps in classifying them as exothermic or endothermic.

Chemical Reactions and Heat Transfer

Chemical reactions can either absorb or release heat, depending on the nature of the reactants and products. For instance, the combustion of a sparkler is an exothermic reaction that releases heat and light, while the reaction in a cold pack absorbs heat from the surroundings, making it endothermic. Understanding the heat transfer in chemical reactions is essential for determining the sign of ΔH.