Final answer:
An exothermic reaction is a process that releases heat and has a negative sign for q, while an endothermic reaction absorbs heat with a positive sign for q. Examples include the heat-releasing combustion of an oxyacetylene torch and the heat-absorbing action of a cold pack.
Step-by-step explanation:
An exothermic reaction is a chemical or physical process that releases heat to its surroundings, causing the temperature of the surroundings to increase. This is because the system itself is losing heat, and thus the sign of q (the quantity of heat) for an exothermic reaction is negative. An example of an exothermic process is the combustion reaction from an oxyacetylene torch, which releases not only heat but also light.
On the other hand, an endothermic reaction is characterized by the absorption of heat from the surroundings, leading to a decrease in the surroundings' temperature. The sign of q for an endothermic process is positive since the system is gaining heat. A practical example is the use of a cold pack that absorbs heat and feels cold as a result.