Chem105a Week 7 Notes
Chem105a Week 7 Notes CHEM 105A
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This 3 page Class Notes was uploaded by Emma Morrissey on Friday October 7, 2016. The Class Notes belongs to CHEM 105A at University of Southern California taught by Thomas Michael Bertolini in Fall 2016. Since its upload, it has received 7 views. For similar materials see General Chemistry in Chemistry at University of Southern California.
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Date Created: 10/07/16
10/3/16 Chapter 6 Continued ● State Functions ○ Only depend on initial and final conditions, not the pathway between them ○ Internal energy, enthalpy, entropy, mass, altitude, and density are state functions ● Internal Energy ○ A system’s total amount of kinetic and potential energy ○ Δ E=E finalinitial ○ Δ Ereactioproductreactants ○ Δ EsystemE surrounding ○ Energy is neither created nor destroyed ● Components of energy ○ Heat (Q)- the transfer of energy due to a temperature difference ○ Work (W)- force acting over a distance ○ Q and W are not state functions ○ Δ E=q+w ○ Positive Negative Q System gains heat System releases heat W System gains energy from System releases energy by work done on it doing work ΔE System gains energy System loses energy ● Calorimetry ○ The science of measuring heat ○ Specific heat capacity (C ❑ - the energy required to raise one g of a substance by 1 K ○ Molar heat capacity - the energy required to raise 1 mol of a substance by 1 K ○ The specific heat of water is so large that it can absorb a large amount of heat energy ● Heat ○ When heat flows into a system, the temperature increases ○ q=mC Δs ● Pressure-Volume work ○ Fluids work via volume change according to this formula. The system is often a fluid-filled piston or balloon ○ w=−PΔV ; PV= L*atm=101.3 J ○ When a fluid expands, work is negative ○ Compression is positive ● Constant Volume (Bomb) Calorimetry ○ The reaction whose q is to be measured occurs in an internal steel chamber (bomb) surrounded by water ○ The chamber’s volume is constant, therefore no work is done. Energy is only released as heat ○ Δ E=q=C ΔT ○ qcal=-qrxn ● Enthalpy ○ H≡E+PV ○ Since E, P, and V are all state functions, so is Enthalpy (H) ○ Change in enthalpy is Δ E+PΔV ■ Does not concern with work; only the effects of heat ■ Notice that there is no change in Pressure ○ At constant P, the system’s enthalpy is the energy flow as heat ○ For a reaction at constant pressure, Δ Hreactionproductreactants ○ If Δ H is positive, the reaction is exothermic ● Constant pressure calorimetry (Coffee cup calorimetry) ○ Run at at atmospheric pressure and are used to determine Δ H for reactions in solution ○ Any observed temperature increase is due to release of energy ■ qsolnq rxn∗msΔT ● Compare coffee cup and bomb calorimeters ● Constant Volume Constant Pressure Sealed in steel chamber Open to atmosphere Ignition in O2 atmosphere Reaction in solution Work = 0 Work is irrelevant Instrument cost $10K Instrument cost 10 cents -q=CT -q=mCT Gives change in energy of Gives change in enthalpy of reaction reaction
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