The standard molar enthalpy of vaporization for water is 40.79kJ/mol. What mass of steam is required to release 500 kJ of energy upon condensation?

What does the mass of 0.7891 mol of ferric oxide (fe2o3)

Nebulae are enormous clouds in outer space. they are made mostly of hydrogen gas, helium gas, and dust. some nebulae glow brightly, while others do not. the stars that people see are huge, bright balls of glowing gas. they are made mostly of hydrogen and helium. which statement correctly describes other ways in which nebulae and stars are different? a. stars can form inside a nebula but a nebula can never be produced by any star. b. a star always has a higher density than a nebula. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star.

State one important difference between a physical change and a chemical change?