how will we know that when uand when h are taken

Any Change in the Internal Energy of a System U is due to either the Heat Flow into/out-of the System or due to Work Done by/on the System provided the system's center-of-mass energy does not change,

the first law as ΔU=Q+W

HEAT Q:
Energy Transfer across the System's Boundaries that cannot produce Macroscopic-Mechanical Motion of the system's Center-of-Mass. Energy Transfer at the Molecular Level .

Q = Microscopic Energy flow into (or out of) the System
ENERGY FLOW
INTO:      Q > 0      System Absorbs Heat     Heat --> Sys
 OUT:      Q < 0     System Releases Heat     Sys --> Heat

Some common types of Heat Lost:
        Solids or Liquids
        Gas- Constant Pressure Process
        Gas - Constant Volume Process
        Gas - Constant Temperature Process
        Gas - Adiabatic Process

INTERNAL ENERGY U
Energy Stored in a System at the Molecular Level.
The System's Thermal Energy -the Kinetic Energy of the atoms due to their random motion relative to the Center of Mass plus the binding energy (Potential Energy) that holds the atoms together.

U = Microscopic Energy contained in the System

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regards

Ramesh