What is the term for a solid changing to gas, and gas changing to solid, with out becomming a liquid?

Which type of orbits are found in the principal energy level n = 2 a - s b - s, f c - s, d d - s, p e - s, p, d

17) large amounts of very important metal titanium are made by reacting magnesium metal with titanium tetrachloride. titanium metal and magnesium chloride are produced. a) write the balanced equation for this reaction. b) how many kilograms of magnesium are required to produce 1.00 kilograms of titanium? ( show work, .)

If the enthalpy value for a reaction is negative, what does that indicate about the reaction?