Q$.$Is enthalpy energy related can if be used inter exchangebly with internal energy?

Specifically In the first law of thermodynamics?$($ chemical thermodynamics$)$

:::

m$1$h$1+$ m$2$h$2=$ m$3$h$3($ m$1,$ m$2$ inlet$)($ m$3$ outlet$)$ if yes or no plz say in detail why

I know there is band gaps in insulators and semiconductors $.$ But not it metals

Metals don't have it $($ gap$)$ because of the antibonding and bonding orbitals$($ I.e conduction band and valence band$)$are close $/$ in the conduction band. I KNOW THIS THE RESULT OF ANTIBONDING AND BONDING ORBITALS being overlapped or closed $($ YES OR NO$?)$

Similarily is the reason semiconductor and insulators have band gap is because of the distance between the Anti bonding and bonding orbitals $?$

IF SO THEN WHY IS THERE SUCH A GAP IN COMPARISON OF METALS $($ PLZ REMEMBER I AM ASKING IN TERMS OF ANTIBONDING AND BONDING CONTEXT$)$

what is the reason of this gap between anti bonding and bonding orbital $($ AND PLZ CONFIRM THAT THE REASON OF THIS BAND GAPS IN DIFFERENCE IN INSULATORS AND SEMICONDUCTORS IS INDEED DUE TO GAP BETWEEN THE AB and Bonding orbitals : YES OR NO$)?$