An endothermic reaction lowers temperature in flask so that the flask will freeze and stick to a wet piece of wood. An exothermic reaction in a Styrofoam cup will significantly raise the temperature in the cup.
Endothermic reaction can be cold enough to cause frost bite.
Concentrated sulfuric acid is extremely corrosive. Exothermic reaction can be violent. Wear safety goggles and disposable gloves. Use a insulated glove for the endothermic reaction. For the exothermic reaction, add acid to water slowly.