The phrase "same chemical composition" refers to the fact that two or more substances have the same combination of elements and compounds, resulting in identical molecular structures. Full definition
Stereoisomers are substances which have the same chemical composition, yet differ in the spatial arrangement of their atoms. (sciencedaily.com)
Two stars with the same chemical compositions are likely to have been born in the same molecular cloud. (sciencedaily.com)
«Every star in that cluster will have the same chemical composition, or DNA — these clusters are quickly pulled apart by our Milky Way Galaxy and are now scattered across the sky,» Dr Martell said. (sciencedaily.com)