Question

What does positive `DeltaH` tell about a reaction?

Answer 1

Energy absorbed from the surrounding.

Explanation:

Enthalpy change is equal to the energy supplied as heat at constant pressure

ΔH = dq

So , if ΔH is positive, energy is given to the system from the surrounding in the form of heat.

For example if we supply 36 kJ of energy through an electric heater immersed in an open beaker of water, then the enthalpy of the water increases by 36 kJ and we write ∆H = +36 kJ.

Conversely if ΔH is negative, then heat is given by the system (reaction vessel) to the surrounding.