Portland cement contains some SiO2. Calculate the mass percent composition of silicon in this compound. (enter the percentage with 3 significant figures)

For which one of the following reactions is the value of δh° rxn equal to δh° f for the product? a. 2 h2 (g) + o2 (g) → 2 h2o (l) b. n2 (g) + o2 (g) → 2 no (g) c. 2 h2 (g) + o2 (g) → 2 h2o (g) d. h2o (l) + 1/2 o2 (g) → h2o2 (l) e. none of the above

If 1.63 times 10 negative 4 of helium dissolves in 100.0g of water, what is the concentration in parts per million

What must happen before a body cell can begin mitotic cell division