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Class 28 Friday, October 29th Sections 8 to 8.3b

Balances on Non-Reactive Processes

Reference States & Process Paths Energy Balance Procedures

Using Heat Capacity Data (Tables, Equations, etc) to Calculate ΔU^ and

ΔH^

• Perform all material balance calculations • Write simplified energy balance equation • Select a reference state (phase, T, P) for each species • Construct a table with columns for species, moles in

and U^in or H^in, and moles out and U^out or H^out • Calculate U^i or Hi^ and insert in table • Calculate ΔU or ΔH • Calculate Ws, ΔEk, or ΔEp, if they are present • Solve the energy balance for the unknown (usually Q)

Doing energy balances Acetone is partially condensed out of a gas stream containing 66.9 mole % acetone vapor and the balance nitrogen. If 100 moles/s are fed to the condenser at 1 atm and 65o C and the vapor exits at 5 atm and 35o C, find the required cooling rate and the moles of condensed acetone.

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Acetone is partially condensed out of a gas stream containing 66.9 mole % acetone vapor and the balance nitrogen. If 100 moles/s are fed to the condenser at 1 atm and 65o C and the vapor exits at 5 atm and 35o C, find the required cooling rate and the moles of condensed acetone. Doing NO calculations, how many unknowns do you have?

a) 2 b) 3 c) 4 d) 5

Acetone is partially condensed out of a gas stream containing 66.9 mole % acetone vapor and the balance nitrogen. If 100 moles/s are fed to the condenser at 1 atm and 65o C and the vapor exits at 5 atm and 35o C, find the required cooling rate and the moles of condensed acetone. Doing NO calculations, how many DOF’s do you have?

a) 0 b) 1 c) 2 d) 3

1 atm 65o C 100 moles/s .669 A .331 N2

5 atm 35o C n1 ya yn

n2 Acetone liquid 5 atm 35o C

Q

Acetone is partially condensed out of a gas stream containing 66.9 mole % acetone vapor and the balance nitrogen. If 100 moles/s are fed to the condenser at 1 atm and 65o C and the vapor exits at 5 atm and 35o C, find the required cooling rate and the moles of condensed acetone. n1+n2=100 ya+yn=1 ya*P = p*(35) 33.1=yn*n1

Plan: a) find p* b) find ya c) find yn d) find n1 e) find n2

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1 atm 65o C 100 moles/s .669 A .331 N2

5 atm 35o C 36.45 0.092 acetone 0.908 nitrogen

63.55 moles/s Acetone liquid 5 atm 35o C

What would be a good reference state for acetone?

I.  Liquid at 65o C II. Vapor at 65o C III. Liquid at 35oC IV. Vapor at 35o C

a)  I or II b) I or III c) I, II or III d) I, II or IV e) II, III or IV

1 atm 65o C 100 moles/s (v) .669 A .331 N2

5 atm 35o C 36.45 0.092 0.908

63.55 5 atm 35o C

Note:

Any substance that has tabulated enthalpy/internal energy data has to use the reference state given by that table.

Ideal gases: p. 652 reference state is 1 atm, 25o C

How do you find enthalpy/internal energy changes for substances that do not have tabulated data?

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How do you find enthalpy/internal energy changes for substances that do not have tabulated data?