TASC Physical Science Practice Exam

Endothermic reactions take in energy from the surroundings. The defining feature is that more energy is absorbed than is released, so the overall energy of the system increases. This is why such reactions often feel cold to the touch—the surroundings lose energy as the reaction consumes it. In contrast, releasing more energy than is absorbed would be exothermic, and a reaction with no net energy change would be energy-neutral. Some diagrams show energy as a reactant on the left to indicate absorption, but the essential point is the net energy flow into the system.