Estimate the average values of ΔH and ΔS in this temperature range

In summary, ΔH and ΔS are thermodynamic values that represent the change in enthalpy and entropy, respectively, of a system. It is important to estimate their average values as it provides insight into the thermodynamic behavior of a system. These values can be calculated through experimental data and can be affected by factors such as experimental errors and uncertainties. The estimated average values of ΔH and ΔS have practical applications in industries such as pharmaceuticals and energy production.
  • #1
westy6711
3
0

Homework Statement



The isomerization of 1-butene and trans-2-butene occurs as shown in the table at selected temperatures. Estimate the average values of ΔH and ΔS in this temperature range.

T/Kelvins....K
883.... 1.10
826.... 1.20
779.... 1.36
733.... 1.49
702.....1.63
686.....1.72

The Attempt at a Solution



ΔG = -RTinK

ΔG = - 8.314x883 x ln1.10 = 699.697 = 6.99697 J/mol

ΔH = ln(1.10 ÷1.72) x (1÷883)-(1/686) = 0.447014111 ,

669.697 = ΔH - TΔS

ΔG = ΔH - TΔS

Thats all I've managed so far, and I am sure its wrong. Can someone help me out please, I've been trying for hours!

Many thanks
 
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  • #2
You're on the right track.

You have two unknowns, ΔH & ΔS - they should remain constant at all temperatures within the given range (hence the "average" specification).

So you need two equations, at minimum. If you repeat your calculation for another temperature, that will give you (where d = delta):

dG (at T1) = dH - T1*dS
dG (at T2) = dH - T2*dS

2 equations, two unknowns. Solve for dH & dS.

To be more precise, you can do the calculation for all values (use excel or something) and graph dG vs T. The slope of that graph will be -dS, and the y-intercept will be dH. Be sure to keep your units consistent!

Edit: Actually, I think you definitely need to do the graphical method since they specify 'average'
 
Last edited:

Related to Estimate the average values of ΔH and ΔS in this temperature range

1. What is ΔH and ΔS?

ΔH and ΔS are thermodynamic values that represent the change in enthalpy and entropy, respectively, of a system. Enthalpy refers to the total energy of a system, while entropy refers to the disorder or randomness of a system.

2. Why is it important to estimate the average values of ΔH and ΔS?

Estimating the average values of ΔH and ΔS is important because it allows us to understand the thermodynamic behavior of a system. These values can provide insight into the stability, spontaneity, and energy changes of a chemical reaction or process.

3. How do you estimate the average values of ΔH and ΔS?

The average values of ΔH and ΔS can be estimated through experimental data. By measuring the enthalpy and entropy changes at different temperatures, we can calculate the average values using mathematical equations such as the van 't Hoff equation.

4. What factors can affect the accuracy of the estimated average values of ΔH and ΔS?

Some factors that can affect the accuracy of the estimated average values of ΔH and ΔS include experimental errors, uncertainties in measurements, and assumptions made in calculations. It is important to minimize these factors as much as possible to obtain more accurate results.

5. How can the estimated average values of ΔH and ΔS be used in practical applications?

The estimated average values of ΔH and ΔS can be used in various practical applications, such as in the design of chemical processes and reactions. They can also be used to predict the behavior of a system under different conditions, which is important in industries such as pharmaceuticals and energy production.

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