1) Calculate the work, w , gained or lost by the system when a gas expands from

Question

1) Calculate the work, w, gained or lost by the system when a gas expands from 15 L to 40 L against a constant external pressure of 1.5 atm. 1 L atm = 101 J

2)When 20.00 moles of H2(g) reacts with 10.00 mol of O2(g) to form 20.00 mol of H2O(l) at 25°C and a constant pressure of 1.00 atm. If 1366 kJ of heat are released during this reaction, and PV is equal to -74.00 kJ, then

3)Calculate H in kilojoules per mole of Mg for the reaction, assuming that the heat capacity of the calorimeter is 776 J/C, that the specific heat of the final solution is the same as that of water [(4.18 J/ (gC)], and that the density of the solution is 1.00 g/mL.

Explanation / Answer

Work done = -PdeltaV

where P = external pressure

delta V = change in volume,

here,

P = 1.5atm

delta V = V2-V1 = 40l-15l = 25l

so,w = -1.5atm*25l = -37.5latm

1 l.atm = 101J

so, -37.5latm = -37.5*101 = -3787.5J = -3.787kJ

so,w = -3.787kJ

since sign is negative,the work is done by the system.

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