A Molecular View of Thermodynamics Learning Goal: To use molecular-level diagram

Question

A Molecular View of Thermodynamics

Learning Goal:

To use molecular-level diagrams to predict the signs of thermodynamic properties.

G=RTlnK

G=HTS

relate entropy change, S, enthalpy change, H, free energy change, G, and the equilibrium constant, K, for a given reaction at a given temperature.

Part A

Drag the appropriate items to their respective bins.

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Incorrect; Try Again; 5 attempts remaining

You sorted 2 out of 3 items incorrectly. This reaction reduces the number of gas molecules. What does that indicate about the sign of S?

Part B

For the gaseous reaction shown here, the bins below represent three different possibilities for the equilibrium mixture. Classify each mixture by what it indicates about G, K, and lnK for the reaction at standard conditions.

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A Molecular View of Thermodynamics

Learning Goal:

To use molecular-level diagrams to predict the signs of thermodynamic properties.

The equations

G=RTlnK

and

G=HTS

relate entropy change, S, enthalpy change, H, free energy change, G, and the equilibrium constant, K, for a given reaction at a given temperature.

Part A

The image represents a spontaneous, gaseous reaction at a constant temperature T K. Predict whether H, S, and G for this reaction are positive, negative, or zero.

Drag the appropriate items to their respective bins.

SubmitHintsMy AnswersGive UpReview Part

Incorrect; Try Again; 5 attempts remaining

You sorted 2 out of 3 items incorrectly. This reaction reduces the number of gas molecules. What does that indicate about the sign of S?

Part B

For the gaseous reaction shown here, the bins below represent three different possibilities for the equilibrium mixture. Classify each mixture by what it indicates about G, K, and lnK for the reaction at standard conditions.

Drag the appropriate items to their respective bins.

SubmitHintsMy AnswersGive UpReview Part

Explanation / Answer

Solution:- (Part A)

If we look at the diagrams for reactants and products then reactant side has 10 gas molecules where as the product side has 5 gas molecules since association has taken place. So, here number of gaseous molecules has decreased and we know that entropy is the degree of randomness. So, as the number of gaseous molecules has decreased, the entrpy has also decreased. Hence, the sign of delta S is negative.

They say that the reaction is spontaneous and being a reaction to be spontaneous the sign of delta G must be negative.

From Gibb's free energy equation, delta G = delta H - Tdelta S

When delta S is negative then delta H must have to be negative in order to give negative value of delta G. So, for this equation the value of delta H is negative.

So, delta H is negative, delta S is negative and delta G is also negative.

part B) How many blue square are there and how many red circles are there. these numbers could be taken as their equilibrium concentrations if we assume constant volume like 1 Liter for both of them. We know that equilibrium constant, K = [products]/reactants]

So, if blue squares are greater than red circles then K would be greater than 1 (K>1). If K is greater than 1 then lnK would also be greater than 0 (lnK >0).

we know that, delta G = delta G0 + RTlnK

From this equation, delta G >0 when K >1 and delta G0 < 0.

So, we could figure it out if the number of blue squares and red circles are given.

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