When global winds, ocean currents, and other forces move freely across the earths surface.
Answer:
The volume of the system will change and maybe the shape of the system boundary
<span>A) elements and compounds.
Compounds are two combined elements.</span>
Answer:
20.3 kJ of heat is absorbed when 9.00 g of steam condenses to liquid water.
Explanation:
Heat is being consumed during vaporization and heat is being released during condensation.
To vaporize 1 mol of water, 40.66 kJ of heat is being consumed.
Molar mass of water = 18.02 g/mol
Hence, to vaporize 18.02 g of water , 40.66 kJ of heat is being consumed.
So, to vaporize 9.00 g of water, 
of heat or 20.3 kJ of heat is being consumed
As condensation is a reverse process of vaporization therefore 20.3 kJ of heat is absorbed when 9.00 g of steam condenses to liquid water.
Answer:
He developed the concept of concentric electron energy levels
Explanation:
Before Bohr's model, Rutherford's model was proposed. This model explains most of the properties of the atom but failed to explain the stability of the atom.
As per Rutherford's model, electrons revolve around the nucleus in the orbit.
But revolving electron in their orbit around nucleus would give up energy and so gradually move towards the nucleus and therefore, eventually collapse.
Bohr's proposed that the electrons around the nucleus move orbit of fixed energy called "stationary states". Electrons in these stationary states do not radiate energy.
Therefore, proposal of concentric electron energy levels refine the atomic models.
