The gas mixture inside one of the cylinders of an automobile
engine expands against a constant external pressure of
0.98 atm, from an initial volume of 150 mL (at the end of
the compression stroke) to a final volume of 800 mL. Calculate
the work done on the gas mixture during this process,
and express it in joules.

Question

The gas mixture inside one of the cylinders of an automobile
engine expands against a constant external pressure of
0.98 atm, from an initial volume of 150 mL (at the end of
the compression stroke) to a final volume of 800 mL. Calculate
the work done on the gas mixture during this process,
and express it in joules.

anonymous · Answer

Try putting these values into proportions, remember the relationship between pressure and volume is pressure/volume.

rock_mit182 · Answer

are you sure tht's all cause i tought im on first law of thermodynamics.. is that simple ?

accessdenied · Answer

Work = Change in (P * V)
    Pressure is force per unit squared,  V is unit cubed.  Notice the units cancel to leave force times unit length, like work = force * distance.

   P is constant, so this simplifies further to:
Work = P * Change in V.

  The unit left over is mL * atm.  From there, we just need to determine the conversion factor between the two.

rock_mit182 · Answer

Oh thanks a lot bro !

rock_mit182 · Answer

when i know in this cases if the work is positive or negative ?

accessdenied · Answer

Sorry I stopped and decided I'd look it up because I wasn't certain of my answer: I think this summed it up nicely. "If energy is transferred to a system as work, the internal energy of the system increases and w is positive E.g., compressing a gas in an insulated container If energy leaves the system as work, the internal energy of the system decreases and w is negative. E.g., allowing the gas to expand again." -- Source: http://www.austincc.edu/dlyon/gen_chem_1_summer04/Chapter%2015b%20thermodynamics%20sp08.pdf In this case, the gas is expanding outwards because the gas is increasing in volume. So the system loses potential energy as work pushing away the cylinder through kinetic energy. Does that make sense put that way?

anonymous · Answer

//Oops, sorry. Didn't realize this was thermodynamics. I thought you were doing gas laws xD

rock_mit182 · Answer

@anitasonia98  don't worry thanks for your help anyway ;9

rock_mit182 · Answer

@AccessDenied  really for the info and the whole explnation,  I appreciate  it

accessdenied · Answer

Yup, glad to help!  :D