Elementary Principles 249 - 7.8 E p = mgz = 105 m3 103 L 1...

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7- 4 7.8 ΔΔ ± ± . . Em g z p == −× ⋅⋅ =− × 10 m 10 L kg H O m m N 1 J 2.778 10 kW h h 1 m L s 1 kg m/ s 1 N m kW h h 53 3 2 32 2 1 981 75 1 1 204 10 7 4 The maximum energy to be gained equals the potential energy lost by the water, or 2.04 10 kW h 24 h 7 days h 1 day 1 week kW h week (more than sufficient) 4 ×⋅ 343 10 6 . 7.9 (b) QW U E E kp −= + + Δ Δ Δ E E k p = = 0 0 system is stationary no height change bg QW UQ W −= < > Δ ,, 00 (c) E + Δ QW E E k p = = 0 0 adiabatic , no moving parts or generated currents system is stationary no height change b g Δ Δ Δ U = 0 (d). E + Δ W E E k p = = = 0 0 0 no moving parts or generated currents system is stationary no height change Δ Δ QU Q =< Δ ,0 Even though the system is isothermal, the occurrence of a chemical reaction assures that Δ U 0 in a non-adiabatic reactor. If the temperature went up in the adiabatic reactor, heat must be transferred
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