Can someone help me pls, I do not know how to do this. i am trying to help a friend as well

Problem page gaseous ethane reacts with gaseous oxygen gas to produce gaseous carbon dioxide and gaseous water . if of water is produced from the reaction of of ethane and of oxygen gas, calculate the percent yield of water. be sure your answer has the correct number of significant digits in it.

What pressure will be exerted by 0.675 moles of a gas at 25*c if it is in a 0.750-l container?

What produces wave a)sound b) heats c)transfer of energy d)vibrations