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Thermodynamics: Enthalpy and Entropy

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1. Given that a formation of a bond between two atoms is exothermic and accompanied by an entropy decrease, explain why all chemical compounds decompose into individual atoms if heated to a high enough temperature.

2. Is the dissolution of urea driven by enthalpy or entropy? How do you know this? Give one example of each of a process that is driven by enthalpy, and one that is driven by entropy.

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Hello,

Question 1
The Gibb's free energy equation related to enthalpy and entropy is as follows:

G = H - TS

And if the change Gibb's free energy is less than zero or negative then a reaction will proceed spontaneously.

In the case of decomposition or bond-breaking which is endothermic the change in entropy will be positive due to the formation of more particles.

Therefore, in looking at the equation bond-breaking will be entropy driven: In other words ...

Solution Summary

This solution provides calculations and explanations for various thermodynamic concepts.

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Enthalpy, Entropy, Spontaneous Reactions, & Other Thermodynamics

BCl3(g) + NH3(g) <---> Cl3BNH3(s) (<---> represents equilibrium in this case)

The reaction represented above is a reversible reaction.

(a) Predict the sign of the entropy change, ΔS, as the reaction proceeds to the right. Explain your prediction.
(b) If the reaction spontaneously proceeds to the right, predict the sign of the enthalpy change, ΔH. Explain your
prediction.
(c) The direction in which the reaction spontaneously proceeds changes as the temperature is increased above a
specific temperature. Explain.
(d) What is the value of the equilibrium constant at the temperature referred to in (c); that is, the specific
temperature at which the direction of the spontaneous reaction changes? Explain.

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