# Absolute Entropy

Delta G sub f for Al203 = -1582 kJ/mol

delta H sub f for Al203 = -1676 kJ/mol

1. Calculate absolue entropy for S for oxygen (g) if:

S for Al(s) = 164 J/mol K

S for Al2O3 (s) = 51.0 J/mol K

2. Calculate the heat required to raise the temperature of 35.0 g of aluminum from 800 degrees C to 2600 degrees C

3. To calculate the standard heat of formation of C2H5OH Steps are

a) First write the reaction for the heat of formation of C2H5OH

b) Calculate delta S for the reaction

c) Calculate delta G for the reaction

d) Use the equation relating delta G, delta H and delta S to calculate delta H sub f of C2H5OH

https://brainmass.com/chemistry/energetics-and-thermodynamics/absolute-entropy-4308

#### Solution Summary

The solution answers each question with explanation. The last question is answered with a description of the step-by-step process. The attachment containing the answers is approximately 400 words long.

Absolute entropy, free energy and spontaneity

1) Describe in detail the difference in absolute entropy values for the following pairs:

a) C(s, graphite) and C(s, diamond)

b) HCl(g) and HCl(aq)

c) CH4(g) and CH3CH2CH2CH3(g)

2)

a) Calculate the values of DeltaH° and DeltaS° for the following reaction at 25°C.

b) Use the values from a to calculate DeltaG° for the following reaction at 25°C.

c) Explain fully whether this reaction spontaneous or non-spontaneous at 25°C?

2 CH3OH(g) + H2(g) -> C2H6(g) + 2 H2O(g) @ 25.0°C

3)

a) Use thermodynamics to prove that the reaction shown below is non-spontaneous at room temperature (25 °C).

b) Calculate the temperature at which the reaction would just begin to become spontaneous.

MgCl2(s) + H2O(l) -> MgO(s) + 2 HCl(g)

5) Commercials make the claim that "a diamond is forever." Use thermodynamics to either prove or disprove this claim by calculating:

a) the entropy change.

b) the free energy change for the reaction below, and

c) by comparing DeltaGf° for graphite and diamond.

C(diamond) -> C(graphite)

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