Lecture 8: Thermochemistry Lecture 8 Topics Brown chapter 5 8.1: Kinetic vs. potential energy 5.1 8.2: Transferring energy as heat & work Thermal energy 8.3: System vs. surroundings Closed systems 8.4: First Law of Thermodynamics 5.2 Internal energy of chemical reactions Energy diagrams E, system & surroundings 8.5: Enthalpy 5.3 Exothermic vs. endothermic Guidelines thermochemical equations 5.4 Hess’s Law 5.6 8.6: Calorimetry Constant pressure calorimetry 8.7: Enthlapy of formation 5.7

Thermodynamics is the study of energy tranfer Energy is transferred as pure energy, work or heat. The general process of advancing scientific knowledge by making experimental observations and by formulating hypotheses, theories, and laws. It’s a systematic problems solving process AND it’s hands-on….. Experiments must be done, data generated, conclusions made. This method is “iterative”; it requires looping back and starting over if needed. [Why do you think they call it REsearch?] Often years, decades or more of experiments are required to prove a theory. While it’s possible to prove a hypothesis wrong, it’s actually NOT possible to absolutely prove a hypothesis correct as the outcome may have had a cause that the scientist hasn’t considered.

Thermodynamics & energy transfer Thermodynamics is the study of energy and its transformations. energy work heat Energy is the capacity to do work or to transfer heat. Energy is transferred in one of two ways: 1) causing motion of an object against a force  work 2) causing a change in temperature  heat Heat flow: heat always from hot regions to cold regions p. 163-4

Visualize energy transfer as work & heat It takes energy, in the form of work, to lift this ball of clay to the top of the brick wall. This work increases the potential energy of the ball. The ball may now roll off of the wall, and fall. Potential energy is transformed into kinetic energy. The ball hits the ground. Kinetic energy = zero. That energy is transferred in 2 ways: 1) work to squash the ball flat 2) into heat transferred to the ground p. 163-4

Thermal energy The energy a substance possesses because temperature (its thermal energy) is associated with the kinetic energy of the molecules in that substance. So rank the physical states of water in terms of levels of kinetic energy & temperature. steam > liquid water > ice Heat flows from regions of high temperature to regions of lower temperature. Our discussions of thermodynamics will focus on the transfer of chemical and thermal energy from reacting substances to the surrounding environment as heat. p. 163-4