Enthalpy & Constant Pressure and Volume

[Jonathan Pai 2I]

Why does deltaH=q at constant pressure?

Why does deltaH=q at constant volume?

Thanks CC

[David Effio 1H]

Mathematically, constant pressure deltaH would be represented as:

deltaU = qP + w
w = -P * deltaV, under constant pressure.

Since deltaH = deltaU + (P * deltaV)
deltaH = (qP - P * deltaV) + (P * deltaV)
deltaH = qP

Similarly, the heat content at constant volume, qV, will be the same as deltaH, because:

deltaU = qP + w
w = -P * deltaV

Since deltaV = 0, because pressure remained the same, we get

deltaU = qP - (P*0) = qP

Since deltaU = deltaH at constant volume, deltaH = qP

[Carissa Young 1K]

Thanks for explaining this! I was also kind of confused about deltaH.