lecture+2.105

# lecture+2.105 - Biological Sciences 105 This is how we...

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Biological Sciences 105 Lecture 2, January 6, 2011 Copyright Steven M. Theg, 2011. All federal and state copyrights reserved for all original material presented in this course through any medium, including lecture or print. 1 This is how we ended last time: What are the units of energy? 1 Joule = the work done to accelerate 1 kg by 1 m/s 2 in 1 m. 1 calorie = energy required to raise the temperature of 1 g of water from 14.5°C to 15.5°C. 1 cal = 4.18 J Learn units: giga, mega, kilo, milli, micro, nano Energy transduction: Be aware that energy is constantly being transduced from one kind to another by biological systems: light to chemical (photosynthesis) light to electrical (retina) chemical to heat chemical to kinetic energy (muscles) electrical to chemical (mitochondria, chloroplasts, bacteria) On useful biochemical energy: Your first formula: Δ means "final - initial" Δ G = Δ E - T Δ S G is Gibbs Free energy, E is internal energy, T is temperature in Kelvin and S is entropy. Δ E is the change in internal energy, which is the energy given off or taken up as heat, plus mechanical work done through changes in pressure and volume. Biochemists define enthalpy: H = E + PV. O r Δ H = Δ E + Δ (PV)

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Biological Sciences 105 Lecture 2, January 6, 2011 Copyright Steven M. Theg, 2011. All federal and state copyrights reserved for all original material presented in this course through any medium, including lecture or print. 2 At constant pressure, which is almost always true in liquids and solids (biochemistry), it can be shown that enthalpy and internal energy are the same, and equal the heat given off or absorbed during the chemical process. Enthalpy is a measure of the energy available in the chemical bonds holding the molecule together. If it gives up heat going from one state to another, the enthalpy (or energy content) goes down. According to the above definition, Δ G = Δ H - T Δ S Δ S is the change in entropy, a measure of disorder. High S means more disorder. Δ G is the change in Gibbs free energy. This is the total energy available for chemical work, both from breaking or forming bonds ( Δ H) and from the change in entropy (T Δ S). If a reaction runs spontaneously, it is referred to as exergonic. If it requires energy input to run, the reaction is said to be endergonic . Spontaneity of chemical reactions: Equilibrium constant for X Y, K eq = [Y]/[X] G is lowest at equilibrium. How can you predict the direction of the reaction by knowing its position with respect to equilibrium? Which formulation of the 2 nd law tells you about direction? Can see now that/why a reaction with a negative Δ G will proceed spontaneously.
Biological Sciences 105 Lecture 2, January 6, 2011 Copyright Steven M. Theg, 2011. All federal and state copyrights reserved for all original material presented in this course through any medium, including lecture or print. 3

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lecture+2.105 - Biological Sciences 105 This is how we...

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