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Thermodynamics  “Thermodynamics is a funny subject. The first time you go through it, you don't understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don't understand it, but by that time you are so used to it, it doesn't bother you anymore.” Arnold Sommerfeld, German theoretical physicist

What is Thermochemistry? (aside from being loads of fun, of course!)  Thermochemistry is the study of the relationship of heat and chemical reactions  Can tell us  Whether a reaction will occur  What drives a reaction  In complex, systems, we can use thermochemistry in combination with structural information to help elucidate mechanisms

The wonderful things you can do with Thermochemistry or How aminoglycoside antibiotics kill bacteria  Studying small changes in the heat absorbed or evolved by the system can tell us how this works DNA  RNA  (bacteria use different “machinery”) Protein /

Aminoglycoside-rRNA Binding

Energy and Chemical Reactivity

Types of Energy

The First Law of Thermodynamics  Conservation of Energy= Energy is neither created nor destroyed  This means that  E universe = 0  During a chemical or physical change, energy will be transformed from one type to another

Energy Interconversion Wind moves turbine Turbine produces electricity Electricity is used to lyse water into H 2 and O 2 H 2 is stored and then burned

JkJcalkcalBTUkWh 1 J = x x kJ = x cal = x x kcal = x kWh =3.6 x x x x Energy Units  Read as 1J = cal

Temperature and Heat  Heat (q) and Temperature (T) are not the same!  The more thermal energy something has, the greater the motion of its atoms  The total thermal energy in an object is the sum of the individual energies of all the atoms, molecules, or ions

What happens to thermal (heat) energy?  Warms another object (transfer)  Causes a change of state  Is used in an endothermic reaction

Which statement below best describes the process of placing a thermometer initially at 22ºC into ice water? 1.Some of the thermal energy of the ice water is transferred to the thermometer. 2.Some of the thermal energy of the thermometer is transferred to the ice water, melting some of the ice. 3.The atoms of mercury begin to move faster as a result of the thermal energy transfer between the thermometer and the ice water. 4.The mercury in the thermometer begins to expand as a result of the thermal energy transferred.

Heat Transfer  If heat (q) is transferred, in which direction does it go?  From hotter to cooler (related to the 2 nd Law, but we’ll get to that later)  Heat lost = Heat gained (1 st Law) q warmer = -q cooler  Thermal equilibrium= when two objects in contact reach the same temperature

System and Surroundings  System = The thing under study  Surroundings = Everything else in the universe  Energy transfer between system and surroundings  Exothermic- system gives off heat  Endothermic- system takes in heat

Heat Transfer  When I heat an object, how much energy will it require? It depends... 1.Quantity (How much stuff do I have?) 2.Size of the temperature change 3.Identity of the material