[Dolphinsiu]

I still feel very confused in two forms of q

q_v = delta U (constant volume) ---- (1)

q_p = delta H (constant pressure) -----(2)

delta H = delta U + pV ---- (3)

All parameters are state function.

However, when do we use Equation 1 ? and when we use Equation 2?

Also,

Are Equation (3) applicable in both cases, at constant volume and at constant pressure? If yes, will the value in pV differ in these two cases?

Also,

If at constant pressure, will the parameters in Equation (1) be all zero?

[Yggdrasil]

q_v = delta U (constant volume) ---- (1)

This equation is valid only for processes occuring at constant volume.

q_p = delta H (constant pressure) -----(2)

This equation is valid only for processes occuring at constant pressure.

delta H = delta U + pV ---- (3)

This should be ΔH = ΔU + Δ(PV), and this equation is valid for all processes.

If at constant pressure, will the parameters in Equation (1) be all zero?

You cannot use equation (1) for a constant pressure process because equation (1) holds only for constant volume processes.

[Dolphinsiu]

Thank you very much!