Why are chemical changes considered “unseen”?

Match the words in the left column to the appropriate blanks in the sentences on the right. (a) this is the law of definite proportions: all samples of a given compound, regardless of their source or how they were prepared, have proportions of their constituent elements. (b) this is the law of conservation of mass: in a reaction, matter is neither created nor destroyed. (c) this is the law of multiple (c) this is the law of multiple blank: when two elements form two different compounds, the masses of element b that combine with 1 g of element a can be expressed as a ratio of small whole-numbers. in this example, the ratio of \rm o from hydrogen peroxide to \rm o from water = 16: 8 \to 2: 1, a small whole-number ratio.: when two elements form two different compounds, the masses of element b that combine with 1 g of element a can be expressed as a ratio of small whole-numbers. in this example, the ratio of o from hydrogen peroxide to o from water = 16: 8 → 2: 1, a small whole-number ratio.