Explain the significance of the sign of the enthalpy value (+ or -). Provide a specific example

Answer 1

By convention, a + sign for enthalpy means that heat is being added to the system from the surroundings.

A - sign for enthalpy means that heat is being released by the system to the surroundings.

Example of an endothermic process would be melting ice. Heat must be added to the system in order to melt the solid ice and convert it to liquid water. There are many other examples.

Example of an exothermic process would be the rusting of iron to form iron oxide. In this process (oxidation/reduction), heat is given off by the system to the surroundings. There are many other examples.