1 What is energy?

Transcription

1 1 What is energy? the capacity to do work? (Greek: en-, in; + ergon, work) the capacity to cause change to produce an effect? a certain quantity that does not change in the manifold changes which nature undergoes (Richard Feynman) 2 Kinetic energy: the energy of motion (e.g., translational energy, heat or thermal energy, light energy, electrical current energy, etc.) Potential energy: stored energy in a resting object due to location (e.g., gravitational energy, electrical battery energy, etc.) or structure (e.g., chemical energy, elastic energy, mass energy) 3 1

2 4 First Law of Thermodynamics: Conservation of Energy Energy can be transferred or transformed, but it can be neither created nor destroyed The quantity of energy before and after a process or reaction is a constant ( E T = E T,f - E T,i = 0)

3 Energy Pies Translational energy Rotational energy Kinetic energy Potential energy Nuclear energy Vibrational energy Electronic energy Physical phenomena Chemical phenomena 7 Electronic Vibrational Rotational Translational energy levels energy levels energy levels energy levels

4 Second Law of Thermodynamics: Entropy Law Energy spontaneously disperses from being localized (or concentrated) to becoming spread out if it is not hindered; energy gradients are dissipated if this is not hindered So, during every energy transfer and transformation energy spontaneously disperses from being localized (or concentrated) to becoming spread out if it is not hindered; during every energy transfer and transformation energy gradients are dissipated if this is not hindered 10 What is entropy? a measure of disorder? a measure of randomness? a measure of the spontaneous dispersal of energy (or dissipation of energy gradients): how much energy is spread out in a process, or how widely spread out it becomes (or some combination of the two) -- as a function of temperature 11 Second Law of Thermodynamics: Entropy Law Energy spontaneously disperses from being localized (or concentrated) to becoming spread out if it is not hindered So, during every energy transfer and transformation energy spontaneously disperses from being localized (or concentrated) to becoming spread out if it is not hindered So, during every energy transfer and transformation entropy increases; after a process there is always more entropy (in the universe) than before the process ( S T = S T,f - S T,i > 0) 12 4

5 Electronic Vibrational Rotational Translational energy levels energy levels energy levels energy levels 13 Universe = System + Environment Isolated systems: those that exchange neither energy nor matter with the environment Closed systems: those that exchange energy, but not matter with the environment Open systems: those that exchange both energy and matter with the environment 14 Universe = System + Environment E universe = E system + E environment = 0 S universe = S system + S environment >

6 G = H system - T S system Gibb s free energy (kj/mole); portion of a system s energy that may be available to perform work when the temperature and pressure are uniform throughout the system Entropy (kj/mole K); measures the dispersal of energy Absolute temperature (K) Enthalpy (kj/mole); estimates the total internal energy in biological systems (constant temperature and pressure; in other systems also includes a term for pressure-volume changes) 16 G = G f - G i G = (H sys,f -TS sys,f ) - (H sys,i -TS sys,i ) G = H sys,f - H sys,i -TS sys,f +TS sys,i G = H system - T(S sys,f -S sys,i ) G = H system - T S system 17 G = H system - T S system The change in free energy is always negative for the system in an actually occurring reaction or process ( G system <0); this provides a qualitative and quantitative assessment of the reaction or process Systems often decrease their enthalpy during a reaction or process: they evolve heat or go from fewer bonds to more bonds or from weaker bonds to stronger bonds or more than one of the above ( H system <0) Systems often increase their entropy during a reaction or process; they go from a lower probability to a higher probability state ( S system >0) 18 6

7 19 Example 1: Formation of Snowflakes

8 G = H system - T S system G: >0 or <0? S: >0 or <0? H: >0 or <0? 22 G = H system - T S system G: >0 or <0? S: >0 or <0? H: >0 or <0? 23 G = H system - T S system G: >0 or <0? S: >0 or <0? (-T S: >0 or <0) H: >0 or <0? 24 8

9 G = H system - T S system G: >0 or <0? S: >0 or <0? (-T S: >0 or <0) H: >0 or <0? 25 Example 2: Burning Methane CH 4 [g] + 2 O 2 [g] -> CO 2 [g] + 2 H 2 O[g] + energy 26 CH 4 [g] + 2 O 2 [g] -> CO 2 [g] + 2 H 2 O[g] + energy ΔG o = -801 kj/mol does ΔH o or ΔS o contribute the most to this?

10 CH 4 [g] + 2 O 2 [g] -> CO 2 [g] + 2 H 2 O[g] + energy ΔG o = -801 kj/mol; ΔH o = -802 kj/mol Example 3: In Recitation! CaM 4Ca CaM 4Ca Energy (kj/mol) ΔGº ΔHº -TΔSº Thermodynamic parameters Figure 3. Thermodynamic origins of high-affinity Figure 3. Thermodynamic origins of high-affinity binding of Ca 2+ by calmodulin. binding Shown of Caare 2+ by the calmodulin. Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (-TΔS) for the formation of the CaM4Ca 2+ complexes. Figure 1. Space-filling model of CaM without (left) and with (right) Ca 2+ cations. Some nonpolar surfaces are shown in green and yellow. Red asterisks indicate the binding sites for target proteins or peptides. ΔHº binding = ΔHº CaM + ΔHº Ca2+ + ΔHº water ΔSº binding = ΔSº CaM + ΔSº Ca2+ + ΔSº water 30 10

11 Clathrate structure These H 2O molecules are more structured and less labile than the bulk H 2O. These H 2O molecules are more structured and more labile than the bulk H 2O. 31 G = H system - T S system 1. G < 0 the reaction or process is spontaneous, thermodynamically possible, and exergonic; predicts the maximum amount of work the reaction could perform 32 G = H system - T S system 2. G = 0 the reaction or process is at equilibrium, no work can be done; for aa + bb cc + dd c d [ C] [ D] G = G + RT ln ( a b ), [ A] [ B] G = RTlnK eq, so tells the extent to which a reaction can occur 33 11

12 G = H system - T S system 3. G > 0 the reaction or process is not spontaneous, not thermodynamically possible, and is endergonic; predicts the minimum amount of energy required to drive the reaction Energy coupling In the cell, a reaction that cannot proceed in isolation (because G > 0) is coupled to another reaction that is sufficiently exergonic ( G < 0) to make the coupled reactions spontaneous K 1 K 2 A B C What is the value of K overall? (Let K 1 = 0.10 and K 2 = 100) 36 12

13 Energy coupling In the cell, a reaction that cannot proceed in isolation (because G > 0) is coupled to another reaction that is sufficiently exergonic ( G < 0) to make the coupled reactions spontaneous A B C [ B] eq [ C] eq K K2 100 [ A] [ B] eq K 1 K 2 eq K overall [ C] [ A] eq eq K 1 K Energy coupling In the cell, a reaction that cannot proceed in isolation (because G > 0) is coupled to another reaction that is sufficiently exergonic ( G < 0) to make the coupled reactions spontaneous o o G 1 G 2 A B C o What is the value of G overall? 0 Let G o RT ; G2 4.61RT. 38 Energy coupling In the cell, a reaction that cannot proceed in isolation (because G > 0) is coupled to another reaction that is sufficiently exergonic ( G < 0) to make the coupled reactions spontaneous o G 1 o G 2 A B C G o 1 RT ln K RT G o 2 RT ln K RT o Goverall RT ln Koverall 2. 31RT 39 o o o Goverall G1 G2 13

14 Energy coupling In the cell, a reaction that cannot proceed in isolation (because G > 0) is coupled to another reaction that is sufficiently exergonic ( G < 0) to make the coupled reactions spontaneous A B C A B Sequential coupling C D Simultaneous coupling has pk a have pk a H + + H 2 O

15 43 44 ΔGº' = ΔHº' TΔSº' ΔGº' = kcal/mol ΔHº' = kcal/mol (57%) TΔSº' = kcal/mol (43%) 45 15