Chemical Properties are different from physical ones, so it cannot be determined by simple observations.
You can determine Chemical properties by performing experiments that will give you hints about the chemical properties of that substance. Some Chemical properties that can easily be tested are as following:
Heat of Combustion
Reactivity with other chemicals
Unlike Chemical properties, Physical properties are much easier to determine.
Simple, nice pictures on this page: https://www.wyzant.com/resources/lessons/science/chemistry/chemical-properties-of-matter