Which of the following observations would indicate that a material is a pure substance?
it does not dissolve in water.
it changes color after heating,
it cannot be physically broken down into different types of atoms.
it can be physically broken down into different types of molecules

Determine the empirical formula of a compound containing 40.6 grams of carbon, 5.1 grams of hydrogen, and 54.2 grams of oxygen. in an experiment, the molar mass of the compound was determined to be 118.084 g/mol. what is the molecular formula of the compound? for both questions, show your work or explain how you determined the formulas by giving specific values used in calculations.

Idon’t know how to solve this question

The bond energy for the van der waals bond between two helium atoms is 7.9×10−4ev. assuming that the average kinetic energy of a helium atom is (3/2)kbt, at what temperature is the average kinetic energy equal to the bond energy between two helium atoms