1. 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

2. 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

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

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

6. 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

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

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

9. 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

10. 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

11. System and Surroundings

12. 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?

13. 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.

14. E, q, w, and Their Signs

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

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

17. w and q are NOT State Functions

18. Work

19. Example
A balloon is cooled by removing 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?