Change in enthalpy equation [closed]








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If the formula for change in enthalpy is ΔH=ΔU+pΔV, and ΔU = q - pΔV then shouldn't the formula be simplified to ΔH = q regardless of whether the volume or pressure is constant? Is this only true when pressure and volume is constant?




The general formula is $\Delta H=\Delta U + \Delta (pV)$.


Since $\Delta U=q\_v$ (heat at constant volume), then $\Delta H=q\_V+V\Delta p$, so no, heat at constant volume does not equal enthalpy, unless p is constant, which just brings you back to the original relation $\Delta H = q\_p$.


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