# Why is U the symbol for lattice energy?

I often see $$U$$ or even $$\Delta U$$ being the symbol for lattice energy. Why is that? Does it refer to internal energy?

• Yes, it corresponds to the internal energy of the crystal. IUCr uses a more well-thought symbol $U_\mathrm{L}.$ – andselisk Feb 18 at 14:23
• Why do we use $\Delta U$ and not $\Delta H$? Is the measurement of lattice energy done at constant volume, or something? – Quantonium Feb 18 at 15:46
• @Quantonium I suppose because the lattice energy it is the internal energy of the lattice. – Alchimista Feb 20 at 13:36