Reactions with Gases Summary Equivalences Moles coefficients in equations stoichiometry Grams Volume of gases ConcepTest What volume of carbon dioxide measured at STP can be produced by the thermal decomposition of 200 0 mg of CaCO3 A 44 8 L PV nRT B 22 4 mL C 0 0448 L 0 2 g 100 09g 0 002 mol D 0 224 L E none of these V nRT P 0 002 mol x 0 0821 x 273 K 1 atm Dalton s Law PTOTAL PA PB PC Mixture sum of pressures of individual gases Partial pressures ConcepTest What is the partial pressure of oxygen in the atmosphere at 760 torr A 20 9 torr B 2 09 atm C 2 09 torr D 0 209 atm E none of these 760 torr x 0 2094 159 144 torr x 1 atm 760 torr 0 209 atm Mixtures and Partial Pressures Dalton s Law pressure exerted by mixture of gases is sum of partial pressures of individual gases Atmospheric pressure due to sum of components Ex Mask Tank of 100 O2 increasing O2 increasing pressure 0 4 to 1 0 Dalton s law Vapor pressure pressure exerted by substance s vapor over the substances liquid at equilibrium o Vapor pressure of water increases with temperature Pressure of gas collected over water is sum of pressure of substance plus water vapor Gas formed passing through tube which goes underneath into the flask then gas comes out at bottom of upside down flask and displaces the liquid in the flask that s in the bowl o Gas could dissolved in water most gases are only sparingly soluble o Some amount of water vapor would be in that gas ConcepTest A sample of nitrogen was collected by displacement of water at 25 0 C The atmospheric pressure was 778 torr and the vapor pressure of water at 25 0 C is 24 torr What pressure would the dry nitrogen exert in the same container A 760 torr B 754 torr C 736 torr D 24 torr 778 torr 24 torr 754 torr ConcepTest What is the mole fraction of nitrogen in the atmosphere E none of these A 100 78 09 B 100 20 9 0 93 0 03 C 0 209 D 7 81 E 0 781 F none of these Mole fraction nA Number of moles of A divided by total moles Dimensionless For gases can be defined by partial pressure and total pressure o nA PA PTOTAL Kinetic Molecular Theory Energy considerations Kinetic energy of gas proportional to absolute temp Average kinetic energies of molecules of different gases equal at given temperature KE mv 2 Average speed v peak of graph