Wednesday, May 18, 2011

Final Exam Review

26) Most of the time, gases behave like ideal gases and the equation PV=nRT can be used for prediction. However, molecules that are polar(hydrogen especially) and/or are large and take up more space tend to deviate the most from the ideal behavior, making it no longer possible to use the above equation for prediction. The gases that do have volume that will resist compression and will form more dense states(i.e. solids and liquids) and gases that have intermolecular attractions that allow them to form liquid and solids are the ones that deviate. Another condition that makes gases act the least like ideal gases is high temperature and low pressure.

Heres a funny video that may help you remember the gas laws and concepts:

31) A)Which non-metals, apart from hydrogen, are most often involved in hydrogen bonding? Why these and not others? 

B) Ethanol and dimethyl ether have the same molecular formula C2H6O. Ethanol boils at 78.4°C whereas dimethyl ether boils at -23.7°C. Using their structures (pictured below), explain why the boiling point of the ether is so much lower than the boiling point of the ethanol.

A) They are Oxygen, Nitrogen, and Flourine. The large difference in electro-negativity in these bonds create stronger dipoles. 
B) In Ethanol, there is a hydrogen bond between H and O. A hydrogen bond is much stronger than the other Van der Waals forces. When melting and boiling, one is acutally breaking the bonds. So, it is much harder to break the hydrogen bonds due to the stronger force and therefore, the boiling temperature must be higher.