Chemistry 141 Wednesday, October 18, 2017 Lecture 18 Gas Mixtures Chemistry 11 - Lecture 11 9/30/2009 Chemistry 141 Wednesday, October 18, 2017 Lecture 18 Gas Mixtures Energy and Enthalpy

Gas mixtures What happens when two different gases are mixed together? Consider equal volumes at constant T: how do the pressures of these samples relate to each other? + = ni + nj = ntotal

Chemistry 11 - Lecture 11 9/30/2009 Gas mixtures A mixture containing 0.100 mol O2, 0.400 mol CH4, and 0.500 mol SO2 gases in a 40.0 L container at 127°C exerts a total pressure of 0.821 atm. What is the partial pressure exerted by CH4? Ans: A (0.328 atm)

Questions The amount of CO2 in the atmosphere is changing with time. How much CO2 is there and how big is the change?

https://www.esrl.noaa.gov/gmd/ccgg/trends/index.html

Take home messages Gas molecules act independently of one another Therefore, in determining the pressure exerted by a gas, only the total number of particles matters, not the identities of the particles The pressure exerted by each type of gas in a mixture is proportional to its mole fraction The pressures exerted by individual gases add to give the total pressure of a gas mixture The identity of the gas does affect the gas density, since density depends on the molar mass of the gas

Energy Potential energy is energy an object possesses by virtue of its position or chemical composition.

Energy Kinetic energy is energy an object possesses by virtue of its motion

Energy Potential energy is energy an object possesses by virtue of its position or chemical composition. Kinetic energy is energy an object possesses by virtue of its motion

Work and Heat Work Heat Energy used to move an object against a force Energy used to cause the temperature of an object to rise

System and Surroundings

Example Calculate the kinetic energy of a 1200 kg automobile moving at 18 m/s. What happens to this energy when the automobile brakes to stop?

First Law of Thermodynamics Energy is neither created nor destroyed. The total energy of the universe is a constant If the system loses energy, it must be gained by the surroundings, and vice versa.

E, q, w, and Their Signs

Heat Exchange Endothermic Exothermic Thermite reaction: Fe2O3 + 2 Al → 2 Fe + Al2O3

State Functions The final state does not depend on the path to get there.

w and q are NOT State Functions

Work

Example A balloon is cooled by removing 0.655 kJ of heat. It shrinks on cooling, and the atmosphere does 382 J of work on the balloon. What is the change in internal energy? Is the process endothermic or exothermic?