chemistry 103 ch 5-7 teachers notes

# chemistry 103 ch 5-7 teachers notes - Chapters 5-7 Teachers...

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Chapters 5-7 Teacher’s Notes Chapter 5 Notes from Prof - Thermodynamics = science of heat and work - Basic Principle of Energy (Ch 5.1) Energy = capacity to do work 2 Forms of Energy: 1. Kinetic Energy Lance Armstrong riding up a mountain Translation, rotation, and vibration of molecules = thermal energy 2. Potential Energy Lance at top of mountain Energy stored in fuels and food = chemical energy Law of conservation of matter Total energy of universe is constant Total energy content is same before and after event 1 5 2 4 3 1. Kinetic energy-ball suspended in air 2. Kinetic and Potential energy-falling 3. Deformation-squished on ground 4. Kinetic and Potential-bouncing back up 5. Potential (energy conserved)-suspended Systems, Surroundings, and Heat Transfer System = object, or collection of objects, being studied Surroundings = everything outside system that can exchange energy and/or matter with system Energy Transfer-heat transferred from object at higher temperature to object at lower temperature (continues until both objects have same Tfinal = thermal equilibrium) - Specific Heat Capacity, C (Ch 5.2) q = C x m x ∆T C = energy transferred as heat required to raise the temperature of 1g of sample by 1K q = energy gained or lost as heat m = mass ∆T = change in temperature (in K) e.g. Calculate energy transferred as heat required to raise T of 10.0g Cu sample from 298K 598K m = 10.0g ∆T = 598K-298K = 300K C = 0.385 J/gxK

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q = (0.385 J/gxK)(10.0g)(300K) = + 1160J e.g. What is Cglycol if 59.8J are required to raise T of 25.0g sample by 1K Cglycol = q/mx∆T = 59.8J/25.0gx1.00K = 2.39J/gxK In isolated system the sum of energy changes = zero hot metal H2O qH2O + qmetal = 0 - Energy and Changes of State (Ch 5.3) So far we discussed energy transferred as heat required to increase T of a sample q = C x m x ∆T Heat of fusion : solid liquid ∆T = 0 For H2O: heat of fusion = 333J/g Heat of vaporization : liquid gas ∆T = 0 For H2O: heat of vaporization = 2256 J/g For heat of fusion and heat of vaporization, the state changes but the temperature does NOT change q = m x heat of fusion q = 2000g x 333J/g = 666kJ if only 500kJ is provided to the system, the whole ice cube won’t melt - The First Law of Thermodynamics (Ch 5.4) Change in energy content ∆U = sum of energy transferred as heat (q) + energy transferred as work (w) between system and surroundings ∆U = q + w Note: U = internal energy; sum of potential and kinetic energies of particles in system = HUGE number Most often interested in work associated with change in volume against constant pressure ∆U = qp - P∆V qp = ∆U + P∆V qp = ∆H = change in enthalpy [H = U + PV] w = -P x ∆V - Enthalphy Changes in Chemical Reactions (Ch 5.5) Standard reaction enthalpy: ∆rH Most stable form of reactant or product at P = 1bar and T = 298K
e.g. H2(g) + 1/2O2(g)

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## This note was uploaded on 02/25/2012 for the course CHEM 2142 taught by Professor Roberts during the Fall '10 term at Texas State.

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chemistry 103 ch 5-7 teachers notes - Chapters 5-7 Teachers...

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