Chemistry 2214A/B Lecture Notes - Lecture 11: Joule, Adiabatic Process, Ideal Gas

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29 Jan 2015

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Consider a gas in an insulated cylinder fed with a piston where no heat transfer can take place (q = 0). Processes under q = 0 conditions are called adiabatic processes. Note that u and t are both negative in adiabatic expansion. The expansion can occur reversibly (pressure change is gradual) or irreversibly (against a constant external pressure). One-step change in pressure, expansion against a constant external pressure. Irreversible adiabatic expansion against the same p reaches a different final state from reversible adiabatic. 2 moles of an ideal gas (cvm = 22jk-1mol-1) at 300 k and 1 bar are compressed adiabatically with 2 kj work done to the gas. Calculate the u, h and q if the process is carried out (a) reversibly and (b) irreversibly. Adiabatic: q = 0; it follows that u = w = 2kj. U is the same for both reversible and irreversible adiabatic compression if the same work is done.

Related Questions

A sample consisting of 3.00 mole of argon gas at an initial temperature of 22.0Â°C expands in a cylinder with adiabatic walls from 22.7 L to 32.5 L under the following conditions. What are the values of the work (w), heat (q), and change of internal energy (ÎU) in each case?

(a) Against a constant external pressure of 1.00 bar.

(b) Against a vacuum (free expansion).

An ideal gaseous reaction occurs at a constant pressure of 40.0\({\rm atm}\) and releases 56.7\({\rm kJ}\) of heat. Before the reaction, the volume of the system was 8.80\({\rm L}\) . After the reaction, the volume of the system was 2.40\({\rm L}\) .

Calculate the total internal energy change, \(\texttip{\Delta U}{Delta U}\), in kilojoules.

An ideal gas is confined to a container with a massless piston at the top. (Figure 2) A massless wire is attached to the piston. When an external pressure of 2.00 \(\rm atm\) is applied to the wire, the gas compresses from 4.90 to 2.45\({\rm L}\) . When the external pressure is increased to 2.50 \(\rm atm\), the gas further compresses from 2.45 to 1.96\({\rm L}\) .

In a separate experiment with the same initial conditions, a pressure of 2.50 \(\rm atm\) was applied to the ideal gas, decreasing its volume from 4.90 to 1.96\({\rm L}\) in one step.

If the final temperature was the same for both processes, what is the difference between \(\texttip{q}{q}\) for the two-step process and \(\texttip{q}{q}\) for the one-step process in joules?

an ideal piston that contains a mixture of liquid water and gaseous water. The piston begins at equilibrium conditions, meaning that the external pressure exactly balances the internal pressure inside the piston. Consider that this piston is put through two different thermodynamic processes:

i.The piston is very slowly compressed over a long period of time so that the volume is reduced by 20%. At the end of the process, the piston still contains as mixture of liquid and gas water.

ii.The piston is suddenly and rapidly compressed over a very short period of time so that the volume is reduced by 20%. At the end of this quick compression, the contents of the piston are allowed enough time to come into thermodynamic equilibrium with the heat bath. At the end of the process, the piston still contains as mixture of liquid and gas water.

Which of these processes is irreversible? Which is reversible?

These two processes will require different externally-applied pressures to accomplish. Which one will require higher pressure?

Which process will require more work to be provided from an external source?

Consider two identical cylinders, one which undergoes process i and another that undergoes process ii. Will these two cylinders have the same internal energy u at the end? Why?

Consider two identical cylinders, one which undergoes process i and another that undergoes process ii. Will these two cylinders contain the same entropy s at the end? Why?

Which process causes more heat to be transferred to the heat bath?

Which process causes more entropy to be transferred to the heat bath?

Chemistry 2214A/B Lecture Notes - Lecture 11: Joule, Adiabatic Process, Ideal Gas

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