Section15_Spontaneity

# Section15_Spontaneity - Spontaneity By the end of this...

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Page 1 of 16 Spontaneity By the end of this lecture, you will be able to: (1) State what a spontaneous process is, and decide which processes are spontaneous and which are not. (2) Define entropy in general terms and state the 2 nd law of thermodynamics. (3) Define equilibrium in terms of entropy and spontaneous processes. (4) Understand phase changes in terms of entropy. (5) Understand the presence of highly ordered systems in nature, and why this order is consistent with the 2 nd law of thermodynamics.

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Page 2 of 16 Imagine … You are working as a patent clerk, as Albert Einstein used to do in his early years. One of your clients wants to register a patent for a machine that produces hydrogen from water according to: 2 H 2 O( l ) + heat 2 H 2 ( g ) + O 2 ( g ) The client says that the heat required for this process would come from the water itself, and the only “waste” produced would be ice. The hydrogen generated in this way could be used as fuel for environmentally friendly cars. You don't have to be Einstein to sense that there is something wrong with this design. But why exactly is it not feasible? Note: The process would not violate the 1st law of thermodynamics (conservation of energy)
Page 3 of 16 Spontaneity (Section 17.1) Spontaneous processes occur without outside intervention e.g. , salt dissolving in water water running downhill water freezing at 0 °C, 1 atm Non-spontaneous processes require outside intervention e.g. , conversion of CO 2 and H 2 O to glucose water flowing uphill separation of O 2 and N 2 in air If a process is spontaneous, its reverse is non- spontaneous Recall: Thermodynamics tells us nothing about rate . Spontaneous processes may occur very quickly, or very slowly. What determines whether a process is spontaneous? (a) Consider bringing two blocks of copper together equal mass different temperature no heat exchange with surroundings

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Recall the first law of thermodynamics: Δ E universe = Δ E system + Δ E surroundings = 0 Possibilities (1) (3) are all valid under the first law, i.e. , total energy is constant. But first law doesn
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Section15_Spontaneity - Spontaneity By the end of this...

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