what determines the way an element reacts with other substances?'
Each element is unique in terms of reactivity. Most elements react readily in high temperatures, but some react quicker in the cold. The same tendency is observed in respect to pressure, with most elements reacting as pressure increases. However, some others react as pressure decreases. In terms of internal factors, a higher surface area correlates with greater reactivity because reagents have a greater chance of making contact with the substance.