16 Calculate the percentage composition by mass of Plaster of Paris, CaSO4 H2O.
[H = 1, 0 = 16, S = 32, Ca = 40]
17

Which statement describes the phase change that occurs when dry ice is placed in an open container at room temperature?

Asubstance is held in an open container. its particles move past one another at random speeds but do not leave the container. heat is removed from the system, and the particles slow down. when enough heat is removed, the particles no longer have enough speed to overcome the weak attractive forces between them. when this happens, the substance enters its solid state. the process described above is known as .

Why is any chemical reaction always balanced? give reasons and explain the easiest way to solve the balancing problems in chemical equations with stoichiometric coefficients upto 20 as hit and trial doesn't always work. give full reasoning