Consider a fire syringe similar to the one you used in Secti

Consider a fire syringe similar to the one you used in Section 18.5. It was assumed that when the plunger is pushed in very quickly, the gas compression is adiabatic. What is an adiabatic compression? Is it reasonable to assume the compression is adiabatic? Why or why not? Is it reasonable to assume the compression is adiabatic when the plunger is moved into the glass tube very slowly? Why or why not? Do you think a significant proportion of the air molecules are leaking out of the tube when the air is being compressed? Why or why not.

Solution

(a)An adiabatic process is one in which no heat is gained or lost by the system. The first law of thermodynamics with dQ=0 shows that all the change in internal energy is in the form of work done.

(b) Yes when it is pushed quickly, the heat transfer can not occur with in instantaneous time periods. So there is not enought time for the energy to transfer from one body to other when it is pushed quickly. So it is rational to assume adiabatic. Also it is done very quickly so the time for the gas to leak is very small during which it is very very reasonable to assume adiabatic compression.

(c) It is more reasonable to assume it as isothermal, where there is enought time for the enrgy to be transferred and the temperature of two bodies come to equilibrium. SO in slow processes or tquasi static processes it is wiser to assume an Iso thermal process.

(d)If the nozzle is two small, the volume of gas leaked depends on the pressure to which it gets compressed and other parameters like temperature and diffusion properties. But in general the proportion of gas leaking would be very small and the number of moles or the mass of gas can be assumed constant.