CHEM 204 Lecture Notes - Lecture 2: Heat Capacity Ratio, Bond Energy, Stoichiometry

77 views8 pages

amaranthjackal733

25 Jan 2018

School

Department

Course

Professor

For unlimited access to Class Notes, a Class+ subscription is required.

Document Summary

Since pressure = force/area , thus force = pa, then the work done as the gas expands is: Is it possible to have a greater amount of work for the same increase in volume: suppose there are an infinitesimal amount of weights exerting a total of. Pin pex = dp; pex = pin dp: but since dp is infinitesimally small, (cid:1856)(cid:1848) (cid:3023)(cid:2870) Thus, using the ideal gas law, we can write, The path that the system took to get there is irrelevant: heat, heat is the transfer of energy between to systems at different temperatures, heat is a path function. Once the temperature of both systems is equal, 4. 2 the first law of thermodynamics then heat is irrelevant: the first law of thermodynamics states that energy can be converted from one form to another but it cannot be created nor destroyed (cid:3048)(cid:3041)(cid:3049)(cid:3032)(cid:3045)(cid:3046)(cid:3032)=(cid:3020)(cid:3052)(cid:3046)(cid:3047)(cid:3032)(cid:3040)+(cid:3020)(cid:3048)(cid:3045)(cid:3045)(cid:3042)(cid:3048)(cid:3041)(cid:3031)(cid:3041)(cid:3034)(cid:3046) (cid:3020)(cid:3052)(cid:3046)(cid:3047)(cid:3032)(cid:3040)= (cid:3020)(cid:3048)(cid:3045)(cid:3045)(cid:3042)(cid:3048)(cid:3041)(cid:3031)(cid:3041)(cid:3034)(cid:3046: mathematically, the first law can be written as:

Related Questions

The piston-and-cylinder device of Illustration 3.4-7 is to be operated in reverse to isothermally compress the 1 mol of air. Assume that the weights in the illustration have been left at the heights they were at when they were removed from the piston (i.e., in process b the first 50 kg weight is at the initial piston height and the second is at âh = âV/A = 0.384m above the initial piston height). Compute the minimum work that must be done by the surroundings and the net heat that must be withdrawn to return the gas, piston, and weights to their initial states. Also compute the total heat and the total work for each of the four expansion and compression cycles and comment on the results.

This questions uses Illustration 3.4-7 in Sandler's Chemical Engineering Thermodynamics textbook, Edition 4, as a basis for the description of the system and surroundings.

Challenge: pV work 1

Consider a container with a frictionless piston that contains a given amount of an ideal gas.

Letâs assume that initially the external pressure is 2.20 bar, which is the sum of a 1 bar atmospheric pressure and the pressure created by a very large number of very small pebbles that rest on top of the piston. The initial volume of gas is 0.500 L and the initial temperature is 25Â°C.

Now, you will increase the volume of the gas by changing the external pressure slowly in a way that guarantees that the temperature of the system remains constant throughout the process. To do this, imagine you remove the pebbles one by one slowly to increase the volume by an infinitesimal amount. Every time you remove a weight you allow the system to equilibrate. Your cylinder is immersed in a water bath at 25Â°C, which keeps your gas at the same temperature throughout the whole process.

Remember to use three significant figures for all numerical answers. The margin of error for each numerical answer is 1%. To avoid rounding errors use the unrounded intermediate values in your final calculations.

Note: You may find an equation to solve this problem in a textbook or online, but the goal of this challenge is that you think through the problem and come up with the equation on your own. This problem requires basic calculus, so be ready to integrate!

Part A

What is the volume of the gas when you remove all pebbles?

V
=

SubmitMy AnswersGive Up

Part B

What is the final pressure of the gas?

p
=

bar

SubmitMy AnswersGive Up

Part C

Now consider the work performed by the sytem. What is the sign of w?

negative