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CSU CHEM 113 - Spontaneous Processes

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CHEM 113 1st Edition Lecture 1 Outline of Last Lecture I. Reviewed the syllabus, so no lecture notesOutline of Current Lecture II. Spontaneous Processesa. Spontaneous vs. NonspontaneousIII. Spontaneous expansion of a gasIV. The First Law of Thermodynamics and spontaneous changesV. ΔH and spontaneous changesVI. Freedom of Particle MotionVII. Microstates and dispersal of energyVIII. EntropyCurrent LectureI. Spontaneous Processesa. Spontaneous change occurs without a continuous input of energy from outside the systemi. Spontaneous doesn’t mean the reaction is fastii. Examples:1. Temperature=30°Ca. Ice spontaneously melts into waterb. Water doesn’t spontaneously freeze into ice2. Temperature=-30°Ca. Water spontaneously freezes into iceb. Ice doesn’t spontaneously freeze into waterb. Nonspontaneous change occurs only if the surroundings continuously supply energy to the systemc. All chemical processes require energy (activation energy) to take place but once a spontaneous process has begun, no further input of energy is neededd. If a change is spontaneous in one reaction, it will be nonspontaneous in the reverse directionII. Spontaneous expansion of a gasa. When a valve is opened, the gas spontaneously expands to fill both flasksb. Gas will never move completely into one side againc. This is the same reason why flat bicycle tires don’t re-inflate themselvesIII. The First Law of Thermodynamics does not predict spontaneous changeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Energy is conserved; it’s neither created nor destroyed, but is transferred in the form of heat/worki. ΔE=q+wb. The total energy of the universe is constanti. ΔEsys=- ΔEsurrii. ΔEsys+ΔEsurr= ΔEuniverseIV. ΔH does not predict spontaneous changea. a spontaneous change may be exothermic or endothermici. spontaneous exothermic processes include:1. freezing and condensation at low temperatures2. combustion reaction3. oxidation of iron and other metalsii. spontaneous endothermic processes include:1. melting and vaporization at higher temp2. dissolving of most soluble saltsb. the signs of ΔH doesn’t by itself predict the direction of a spontaneous changeV. Freedom of Particle Motiona. All spontaneous endothermic processes result in an increase in the freedom of motion of the particles in the systemb. A change in the freedom of motion of particles in a system is a key factor affecting the direction of a spontaneous processi. This correlates to a greater dispersal of particle energyVI. Microstates and dispersal of energya. Just as the electronic energy levels within an atom are quantized, a system of particles also has different allowed energy statesb. Each quantized energy state for a system of particles is called a microstatei. At any instant, the total energy of the system is dispersed throughout onemicrostatec. At a given set of conditions, each microstate has the same total energy as any otheri. Each microstate is therefore equally likelyd. The larger the number of possible microstates, the larger the number of ways in which a system can disperse its energyVII. Entropya. The number of microstates (W) in a system is related to the entropy (S) of the systemi. S=kBlnWii. kB is the Boltzmann constantiii. a system with fewer microstates has lower entropyiv. A system with more microstates has higher entropyb. All spontaneous endothermic processes exhibit an increase in entropyc. Entropy, like enthalpy (H) is a state function and is therefore independent of the path taken between the final and initial statesd. Entropy is the measure of how particles are


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CSU CHEM 113 - Spontaneous Processes

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