Final answer:
A higher ionization enthalpy indicates that a substance is chemically more stable, as it is less reactive due to the stronger attachment of electrons to the nucleus. However, a smaller heat of sublimation suggests that the substance is physically less stable, as it requires less energy for the substance to change from a solid to a gas.
Step-by-step explanation:
If the ionization enthalpy were bigger and the heat of sublimation of a substance were smaller, would the substance be more stable or less? The stability of a substance in terms of its ability to remain in the solid state is generally related to the energies involved in transitions between different states (solid, liquid, gas) and the energy required to remove electrons (ionization).
A higher ionization enthalpy means that it requires more energy to remove an electron from an atom or molecule, indicating stronger attachment of the electrons to the nucleus. This contributes to the chemical stability of the substance as it becomes less reactive. However, if at the same time the heat of sublimation is smaller, it implies that less energy is required to change the substance from a solid to a gas state, this could indicate that the physical forces holding the solid together are weaker.
The overall effect on stability would depend on a delicate balance between these two factors. In general, a higher ionization enthalpy would imply more chemical stability, whereas a smaller heat of sublimation suggests less physical stability. Consequently, the substance may become chemically more stable but physically less stable, meaning it would be less likely to react with other substances but more likely to change its phase from solid to gas.