What does a triangle written above the arrow in an equation
represent?

If the reaction requires energy, it is often indicated above the arrow. A capital Greek letter delta (Δ) is written on top of the reaction arrow to show that energy in the form of heat is added to the reaction; hv is written if the energy is added in the form of light.

i think its 5049.

i hope this !

o conteúdo de calor de um sistema é igual à entalpia apenas para um sistema que é constante