Lecture9a

Lecture9a - The Laws of Energy transformation...

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The Laws of Energy transformation Thermodynamics is the study of energy transformations A closed system, such as that approximated by liquid in a thermos, is isolated from its surroundings In an open system , energy and matter can be transferred between the system and its surroundings Organisms are open systems
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The Second Law of Thermodynamics During every energy transfer or transformation, some energy is unusable, often lost as heat According to the second law of thermodynamics, every energy transfer or transformation increases the entropy (disorder) of the universe
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The Second Law of thermodynamics According to the second law of thermodynamics Spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe Figure 8.3 Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism. (b) Heat co 2 H 2 O +
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Living cells unavoidably convert organized forms of energy to heat Spontaneous processes occur without energy input; they can happen quickly or slowly For a process to occur without energy input, it must increase the entropy of the universe
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Biological Order and Disorder Cells create ordered structures from less ordered materials Organisms also replace ordered forms of matter and energy with less ordered forms The evolution of more complex organisms does not violate the second law of thermodynamics Entropy (disorder) may decrease in an organism, but the universe’s total entropy increases
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The free-energy change of a reaction tells us whether the reaction occurs spontaneously Biologists want to know which reactions occur spontaneously and which require input of energy To do so, they need to determine energy changes that occur in chemical reactions
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Free-Energy Change, G A living system’s free energy is energy that can do work when temperature and pressure are uniform, as in a living cell Free energy is a measure of a system’s instability, its tendency to change to a more stable state During a spontaneous change, free energy decreases and the stability of a system increases Equilibrium is a state of maximum stability A process is spontaneous and can perform work only when it is moving toward equilibrium
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The change in free energy (∆ G ) during a process is related to the change in enthalpy, or change in total energy (∆ H ), and change in entropy ( T S ): G = ∆ H - T S Only processes with a negative ∆ G are spontaneous Spontaneous processes can be harnessed to perform work
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Free energy and cell work At maximum stability the system is at equilibrium Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. . Diffusion. Molecules
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Lecture9a - The Laws of Energy transformation...

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