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# UConn CHEM 1125Q - Pressure and Volume

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CHEM 1125Q 1st Edition Lecture 2 Outline of Last Lecture (Ch. 10)I. Energy Changes, Thermochemistry, Thermodynamics, States, Heat, Work, and EnthalpyOutline of Current Lecture (Ch. 10)II. Pressure and VolumeIII. Constant PressureIV. Enthalpy and Enthalpy ChangesA. EnthalpyB. Enthalpy of ReactionV. CalorimetryA. Specific HeatB. Heat CapacityCurrent LectureII. Pressure and VolumeA. Pressure-volume, or PV work, occurs under constant pressure while the volume changesa. When a change occurs at a constant volume, ΔV=0, so no work is doneb. Work equation:w = –PΔVIII. Constant PressureA. There are 3 important equations for reactions under constant pressureΔU = q + wΔU = q – PΔVqp = ΔU + PΔVIV. Enthalpy and Enthalpy ChangesA. Enthalpya. Enthalpy (H) refers to the thermodynamic function of a systemH = U + PVb. For any process the change in enthalpy is:ΔH = ΔU + Δ(PV) (1)c. If Pressure is constant:ΔH = ΔU + PΔV (2)d. Rearrange to solve for ΔU:These 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.ΔU = ΔH – PΔV (3)e. Remember that qp = ΔU + PΔV (4)f. Substitute equation (3) into (4) and solve:qp = (ΔH – PΔV) + PΔVB. Enthalpy of Reactiona. The difference between the enthalpies of products and reactants is measured by ΔHi. ΔH = Hproducts – Hreactantsii. When ΔH > 0, the reaction is endothermiciii. When ΔH < 0, the reaction is exothermicb. Enthalpy is dependent on the amount of matter involved in a reactionV. CalorimetryA. Specific Heata. Calorimetry is the measuring of heat changesb. Specific heat (s) refers to the amount of heat required to raise the temperature of 1g of a substance by 1°CB. Heat Capacitya. Heat capacity (C) refers to the required amount of heat necessary to raise the temperature of an object by 1°Ci. The “object” being a given quantity of a substanceb. Heat that is associated with temperature change can be calculatedc. Equations:q = smΔTq =

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