Question

What is the difference between internal energy, heat, and enthalpy? Are they ever the same?

Please write down and describe a couple of equations that help us understand the relationship between these quantities.

Answer 1

1)

This is a type of energy, it is a CONTENT energy, that is, it may be cointained in the system

Internal Energy = the total energy "inside" of molecules due to temperature.

- Vibrational, transaltional movmeents

- intermolecular forces, chemical bondings

2)

heat = this is a type of ENERGY specially a TRANSFER energy; that is, it must cross between system and surrounding in order to exist.

Heat is the phenomena that exisdts due to change of temperature

heat flow from high T to low T

3)

Enthalpy is a vonenient math propertie

it is essentially

H = U + PV

PV is the concept that exists in open systems, PV element is pretty common for constant Pressure annd changes in V.

All other properties of H are similar to U; that is, it is a function of Temperature and is acontent energy

NOTE:

Q depends a lot on the type of process

i.e.

Q = dH for open systems, constant pressure

Q = dU for closed systems, constant volume

Q = w for adiabatic systems + work

Q= 0 for adiabatic systems and no work

H = Q/dT at constant P only

U = Q/dT at constant V only

you can always relate H and U as follows

H = U + PV