Combustion

Question 1

How do you Calc Internal energy of liquids and solids from enthalpy

Answer 1

ITS THE SAAME ! for liquids and solids at least. because pv is usually negligible. so internal energy = enthalpy.
because Enthalpy is independent of pressure, it follow that neither is internal energy.

Question 2

State the 1st law steady flow energy equation. What is it used for? What’s the equation?

Answer 2

Energy in = Energy out. or Heat + Enthalpy in = Enthalpy out.
Q = change in enthalpy. Q = Sigma(mphp) - (mrhr) see lecture slides.

Question 3

State the eqn of enthalpy at pressure P and Temp T. What is the relation between enthalpy and pressure.
Explain why enthalpy of formation is 0 at 298K and 100kPa

Answer 3

hT = hf(enthalpy of formation) + hT ( enthalpy at temperature T relative to reference temp)
Enthalpy is independent of pressure.
at 298K and 100kPa it’s zero because that is the reference point. The datum being compared with.