NEED HELP ASAP I BOUT TO LEAVE SCHOOL?

0.88 moles of n2o5 (g) was placed in a sealed 1.00 l vessel. calculate the equilibrium concentration of n2o5. no2, and o2 and the equilibrium constant after equilibrium has been reached by 65.0% of the n2o5 decomposing.

What sources of error may have contributed to the percent yield not being 100 percent? think about things that may have led to inaccurate measurements or where mass of the product could have been lost if this experiment was conducted in a physical laboratory.

I'm a tad bit confused on how to name compounds with molar mass and was wondering what was the difference between the formulas dealing with covalent and iconic if someone could pls explain these directions that would be great