Ok, long time lurker who doesn't often post. I think I may be able to help with the chemistry questions. I'd probably prefer to keep most of my limbs though, if it's all the same to you. An amount of 2.0g of dry ice (CO2) is added to an empty balloon. After the dry ice completely sublimes to a gas at 1.0atm and 25C, what will be the volume of the balloon?quote> Ok, this experiment is being conducted at SLC, at which one mol of gas has a volume of 24.5L. As such, the fraction of a mol of gas present will be the fraction of 24.5L which is occupied. So we have 2/(12+16+16) = 0.045mol of CO2 gas. Hence our volume will be 0.0045 x 24.5 = 1.1L (answer should be to two significant figures) An empty 2.5L diving tank is filled with 1.0 mole of helium and 0.25 moles of oxygen at 25C. Calculate the total pressure of the tank.quote> Here we use PV=nRT. We know V=2.5, n=1.25 (amount of hydrogen and oxygen added up), R=8.31 (this is a constant) and T=25+273 = 298 degrees K So, this leaves us with P = 1.25 x 8.31 x 298 / 2.5 (after a little transposition), which gives an answer of 1.2 x 10^3 kPa (to two significant figures). If you're not concerned with significant figures, an easier way to write the answer is 1238 kPa If the barometer reads 751mm Hg, what are the partial pressures of oxygen and nitrogen in the atmosphere?quote> For this question you must use the composition of gases in the atmosphere. The atmosphere is approx 78.1% nitrogen and 20.9% oxygen. To get the partial pressures of these gases, we just multiply the total pressure of the atmosphere by the percentage composition of each gas. So we have 751 x .781 = 587 mm Hg is the partial pressure of nitrogen 751 x .209 = 157 mm Hg, the partial pressure of oxygen. Both ansers are given to three sig figs.
