Supplemental Instruction 1060 Hixson-Lied Student Success Center  294-6624  www.si.iastate.edu Chapter 19: Spontaneous Processes Supplemental Instruction Iowa State University Leader: Kelsey Course: Chemistry 178 Instructor: Verkade Date: 10/26/2010 1. Demo 10/26/2010 = Ammonia Fountain Water is squirted into an inverted flask containing ammonia gas. The ammonia dissolves in the water, creating a vacuum that draws in the water from below. An indicator created the color change from orange to blue. Further explanation: http://www.youtube.com/watch?v=hpSdR2SEaXI 2. The first law of thermodynamics states that energy cannot be CREATED or DESTROYED. This statement is true for all practical purposes in this course. This law is represented by: What does each variable stand for? = the change in internal energy = the heat absorbed by the system from the surroundings w = the work done 3. Circle the correct answers: a. In an exothermic reaction, heat travels from the system/surroundings to the system/surroundings. b. In an endothermic reaction, heat travels from the system/surroundings to the system/surroundings. 4. Circle the correct answers: a. Two eggs dropped spontaneously/non-spontaneously break. b. Two eggs leaping into your hand with their shells back intact is spontaneous/non-spontaneous. c. Define a spontaneous process. A process that is capable of proceeding in a given direction, as written or described, without needing to be driven by an outside source of energy. A process may be spontaneous even though it is very slow. 5. Circle the correct answers:a. Consider the interconversion of ice and water at 1atm, (diagram may be found in today’s lecture notes or on page 803 in the BLBM textbook). Ice and water are in equilibrium, then we add heat to the system from the surroundings. We melt 1 mole of ice to form 1 mole of liquid water. This process is reversible/irreversible. b. Consider a gas in a cylinder with a piston (diagram may be found in today’s lecture notes, or on page 805 in the BLBM textbook). We remove the partition and the gas expands to fill the space. This process is reversible/irreversible. c. Define reversible and irreversible processes. Reversible = process that can go back and forth between states along the same path. Irreversible = process that cannot be reversed to restore the system and surroundings back to their original state. 6. Note that for a spontaneous process, the path between reactants and products is irreversible. For a system at equilibrium, reactants and products can interconvert reversibly. 7. What letters (variables) designate Entropy, Heat, and Enthalpy, respectively? Entropy = S Heat = q Enthalpy = H 8. In the following equation, what do the variables stand for? What is “T” measured in? = change in entropy = reversible heat T=temperature, Kelvin 9. Entropy is a state function. Define entropy and define state function. Entropy = A thermodynamic function associated with the number of different equivalent energy states or spatial arrangements in which a system may be found. (Entropy is a measure of disorder or randomness, ex: a messy bedroom has high entropy because it has a high state of disorder). State Function = A property of a system that is determined by the state or condition of the system and not by how it got to that state; its value is fixed when temperature, pressure, composition, and physical form are specified; P (pressure),V (volume),T(temperature) ,E(energy), and H(enthalpy) are state