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In 1845 Joule showed that mechanical energy (work) and heat were the same thing and used University of Prince Edward Island very precise temperature measurements to calculate the heat content in a foot-pound of work. 1 H Biochemistry6 7 8 C N O Barry Linkletter 15 16 P S In 1847, Helmholtz stated the law of conservation of energy, an important component of the first law. Hermann von Helmholtz James Prescott Joule Sir Benjamin Thompson, 1821-1894 1818-1889 Count Rumford 1753-1814 Lecture 10 Supplement: The Laws of Thermodynamics Benjamin Thompson fought on the Loyalist ...can be stated many ways. Here is a collection of these famous laws. They were side of the American Revolution then developed over many years and were stated by many people in many different ways decamped to Germany to start the Ther- before agreement began to form in the mid nineteenth century. Even then, the modynamic revolution in 1797. He showed third law as not formulated in it’s current form until 1906. that work could be converted to heat through friction, proving that heat was 0: If A B and B C are at equilibrium, then A C must also be at equilibrium. NOT a fluid, but was energy. 1: The increase in internal energy of a closed system is equal to the heat supplied to the system minus work done by it. Thompson also used his 2: Natural processes to lead towards spatial homogeneity of matter and energy, and especially of temperature thermodynamic powers to invent a better 3: The entropy of a perfect crystal of any pure substance approaches zero as the temperature approaches absolute zero. fireplace for Carnot, Clausius, Kelvin and Carathéodory all stated the second law in different ways. They were all correct. English homes. Thomspon married the In 1824 Carnot expressed widow of Lavoisier. the idea of the second law In 1851 Kelvin wrote down what would eventually become the in a study of steam engines. second law. He was discussing the irreversibility of heat flow In 1865 Clausius gave The Carnot cycle is well known and speculated about the heat death of the universe. entropy its name. today and is the basis for the diesel engine.. The video is available on YouTube at https://youtu.be/hE-EspsO3LI How many 17 year old students get a painted portrait? Carnot’s father was a major figure in the In 1909 Carathéodory listed French revolution. the laws of thermodynamics numerically. He could only He died young count to two at that time. from cholera. Nicholas Carnot Rudolf Clausius William Thompson, Constantin Carathéodory 1796-1832 1822-1888 Lord Kelvin 1873-1950 1824-1907 Introduction To Biochemistry: Chemistry Review: Reaction Equilibrium and Kinetics Page 1 of 13 Equilibrium The concept of equilibrium was well known to chemists when Le Chatellier encapsulated the idea in his famous principle, “If you disturb a system that is at equilibrium, it KeynoteChemistry.com will tend to return to equilibrium”. Whether we start with all α- or all β-glucose, we Keq always end up with a ratio for α/β of 1/1.78. Even if A B I dump in more α-glucose, the ratio soon returns to The specific rotation of α/β = 1/1.78. a glucose solution always B ends up at 52.5˚ no matter [ ]eq OH OH where we start. Why? Keq = O Keq O [A]eq HO HO 20 The equilibrium HO H HO OH [ ] = +52.5 OH OH D constant OH H D D = + -D-glucopyranose -D-glucopyranose = + [ ]20 112 [ ]20 18 I didn’t write out For a given set of reaction the units but they conditions, this value remains are important in constant. No matter how we [ ] = = answering the change the concentrations of Keq 1.78 question below. reactants and products, the system [ ] Berthollet first proposed the will return to the equilibrium ratio idea of chemical equilibrium over time. in 1803 when he observed that some chemical reactions were reversible Ponder this... I have 100 mL of a solution of glucose that has been sitting around for days. I measure the optical rotation to to be 10.5˚ dm–1. What is the concentration of glucose? I then add 1g of pure α-glucose to the solution. What is the observed optical rotation immediately after addition, and what will be the optical rotation tomorrow? Tell me the final concentration of α-glucose and β-glucose in the solution. You will need to know the units of specific rotation and the molecular weight of glucose Henry Louis Le Châtelier Claude Louis Berthollet to answer this question. 1850-1936 1748-1822 Introduction To Biochemistry: Chemistry Review: Reaction Equilibrium and Kinetics Page 2 of 13 Gibbs has been honoured Free Energy with a postage stamp. Willard Gibbs developed the connection between equilibrium constant and an energy difference that we now call “free energy”. This is the change in free energy between the reactants in their standard state and the products in their standard state. If we know the equilibrium constant then we know the difference in free energy. Josiah Willard Gibbs G = RT ln Keq 1839-1903 These are both G the same equation. Gibbs wrote the book that was the found- RT ation of Lewis’ text- Keq = e book on chemical thermodynamics Gibbs’ father was a president of Harvard Univeristy and before that a scholar at Yale, Like his son. Gibbs had a ship named after him, He was an abolitionist and he was the USNS Josiah Willard Gibbs part of the Amistad trial in 1840. These 5-inch guns were removed in the name of science. USNS Josiah Willard Gibbs, 1958-1971 Introduction To Biochemistry: Chemistry Review: Reaction Equilibrium and Kinetics Page 3 of 13 Enthalpy and Entropy It was a long and difficult road, filled with bitter rivalry and petty feuds. But many great minds applied the principals of thermodynamics to chemistry and eventually Lewis spent 20 years measuring and agreement was reached for concepts of free energy, calculating free energy changes in enthalpy and entropy. chemical reactions and wrote the book that defined thermodynamics Between 1888 and 1906 le Chatelier, Lewis, Richards, for our modern age in 1923. van’t Hoff, Haber, and Nernst made important contributions to this field. Today we describe free energy as being part “real energy” (enthalpy) and part statistical According to Nernst, inevitability (entropy). he himself stated the third law of thermodynamics. Others disagreed. Haber was jealous Arrhenius and Richards This is quite of van’t Hoff’s campaigned hard against G = H T S a club, isn’t it? hair (I’m kidding). Nernst in the Nobel committee. They delayed his Was Haber a hero recognition until 1920 but his or a war criminal? Richards felt that body of work could not Discuss among your Nernst didn’t give be denied. friends. him credit for his ideas. 14 01 18 20 19 19 19 19 Lewis was Richards’ doctoral student. Lewis never met anyone that he couldn’t turn into an enemy. Gilbert Lewis Theodore Richards Jacobus van't Hoff Fritz Haber Walther Nernst 1875-1946 1868-1928 1852-1911 1868-1934 1864-1941 “Thermodynamics (2nd Edition ed.)”, Lewis, Gilbert Newton; Randall, Merle: Revised by Pitzer, Kenneth S. & Brewer, Leo (1961). McGraw-Hill Book Co., New York, New York, United States: ISBN 0-07-113809-9. Introduction To Biochemistry: Chemistry Review: Reaction Equilibrium and Kinetics Page 4 of 13 Some Observations Observe that the entropy term can work in Equilibrium roles downhill. The free energy of Wait a minute! Hard-core the same direction as enthalpy or in the opposite molecules in solution have been determined in the physical chemists also depending on it’s sign. standard state. demand that [H+] = 1 M. Are we in the wrong? Standard state depends on the field. In biochemistry it is usually 1M in concentration, pH 7.0, 25 ˚C. G = H T S Why not 37 ˚C? But nothing ever happens at 1M in biochemistry. What is the actual free energy difference under more likely concentrations? Imagine a change with ...and positive entropy; negative enthalpy; change is also “downhill” change is “downhill” [P] “products” over “reactants” Do you recall the The change is free energy G = G + RT ln reaction quotient, Q? will always be downhill in this case. [R] Actual free Total difference G if there Can you consider energy for a What is the ∆ ion free energy between other cases? There given system. is no product present? are 4 in total. products and reactants in their standard state. You look these values up in published tables of thermodynamic data Fact: when equilibrium is reached the following is true... [P] G = 0 and K = therefore 0 = G + RT ln K eq [R] eq G = RT ln Keq G RT Keq = e Introduction To Biochemistry: Chemistry Review: Reaction Equilibrium and Kinetics Page 5 of 13 Add it Up Does ATP hydrolysis favour the products? The standard free energy change in a reaction can be combined with that of another reaction if they are Do you think phosphate coupled. Take the first step of glycolysis as an example. salt spontaneously condenses with glucose? 1 5 5.3 ATP + H 2O ADP + Pi G = 30.5 kJ mole Keq = 2.2 10 Keq =10 1 4 3.4 Glc+ Pi G6P + H 2O G = +13.8 kJ mole Keq = 3.8 10 Keq =10 1 2 2.9 ATP +Glc ADP +G6P G = 16.7 kJ mole Keq = 8.5 10 Keq =10 We make the phosphorylation of glucose highly favourable This idea is how ATP drives all Do you believe that ATP by using high energy ATP as the reactant rather than of biochemistry forward.