Enthalpy and Potential Energy - Study Notes

Experiment #1waterpipeinitial temperature25°C100°Cfinal temperature28.7°C 28.7°CΔT3.7°C-71.3°Cmass125 g60gΔT = Tfinal – Tinitialhave two unknowns for the pipe → specific heat (c) and q-use water to calculate itqw = mwcwΔTwqw = (125 g) (4.14 J/g*°C)(3.7°C)qw = 1900 Jq is positive when energy is absorbedamount of energy absorbed is equal to the amount of energy releasedqwater = -qpipeqpipe = -1900 Jcpipe = qpipempipeΔTpipecpipe = -1900 J = 0.4 J/ g*°C(60 g) (-71.3°C)metal of the pipe → Fe (iron)Experiment #2ethanolpipeinitial temperature25°C100°Cfinal temperature31°C31°CΔT6°C-69°Cmass125 g60 gwant to find out specific heat of “ethanol” → not sure if it is ethanol-or whatever Dr. Rosenthal said (so its like solve it without looking at table)Step #1; use cpipe from experiment #1Step #2 calculate qpipe = mpipecpipe ΔTpipeStep #3 ; -qethanol = qpipeStep #4 cethanol = qethanolmethanol -->TethanolNaOH (s)--> NaOH (aq)bottom of the beaker felt hot → energy is being released by the system into the surroundingssystem: NaOH (s) Na+(aq) OH-(aq)surroundings: watertemperature of the water is increasing during the dissolving → energy is being released by the system and absorbed by the surroundings (water)-means that the kinetic energy of the water increased (kinetic energy is a reflection of temperature)-the chemical potential energy of the system decreased-released potential energy→ the ions are spreading apart (the relative positions of the ions changed)-any change in potential energy → called enthalpy change (in this case, exothermic – energy is released)NaOH (s) → NaOH (aq)Potential Energy change = enthalpyEnthalpy – the potential energy change that a system undergoes, reflected by a change in temperature of the surroundings“heat content” (enthalpy) of substancesΔH → symbol for enthalpy ΔH = mcΔTheat content of the water (surroundings) increasesΔH is positive for waterΔH is negative for NaOHConclusions: exothermic reaction (negative ΔH for system → potential energy went down, released by the system)-energy is a product NaOH (s)...

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