Chemical Thermodynamics

We have seen in the previous post, that the Gibbs free energy of a reaction is a comprehensive measure of the spontaneity of the reaction that can be calculated based on the parameters of the system.     Today, we … Read more

Recall how we used the Hess’s law to calculate the enthalpy change (ΔH) for a reaction without having the enthalpies of formation for any or some of the components in the reaction. On the basis of the Hess’s law is … Read more

In the previous post, we talked about the Gibbs free energy for reactions at nonstandard-state conditions, ΔG. It is related to the free energy change of the reaction at standard-state conditions, ΔGo, and the reaction quotient, Q with the following … Read more

In the previous two posts, we talked about the Gibbs free energy and calculating its value using either of these two equations:   ΔG°rxn = ΣnpΔGof (products) – ΣnrΔGof (reactants)  (1) ΔG°rxn  = ΔH° – TΔS°   (2)   There are two main scenarios … Read more

Because free energy, G is a state function, we can calculate the free energy change of a reaction, ΔGorxn by subtracting the free energies of the reactants of the reaction from the free energies of the products of the reaction. … Read more

Because entropy is a state function, we can calculate the entropy change of a reaction if we know the standard entropies, So of the reactants and products. Remember, a state function depends only on the initial and final values and … Read more

On the basis of determining the entropy change associated with phase transitions is the third law of thermodynamics: the entropy of a perfect crystalline substance is zero at the absolute zero temperature.  An implication of this is that the entropy … Read more

In the previous post, we discussed the correlation between the entropy change of the surroundings, ΔSsurr, and the enthalpy change of the system.     This relationship is useful for determining whether a given reaction is spontaneous or not because … Read more

When calculating the enthalpy or any other thermodynamic parameter, we are usually focused on the system. For example, we may use a calorimeter to calculate the enthalpy of a reaction which is the point of our interest, and therefore, it … Read more