Question

When is $\Delta H$ negative and when is $\Delta S$ negative?

Answer 1

1. $\Delta H$ refers to change in enthalpy and $\Delta S$ refers to the change in entropy.
2. Enthalpy refers to the amount of energy released during the chemical reaction whereas entropy refers to the measure of disorders in the system.
3. The free energy equation is given by, $\Delta G=\Delta H-T\Delta S$ Where $\Delta G$ is the free energy of the system.
4. If the enthalpy($\Delta H$) is negative, then it means that the reaction gives off heat from reactants to products(exothermic reaction), which decreases the entropy of the system.
5. Similarly, if the entropy ($\Delta S$) is negative, it means that the disorder of the system is decreasing from reactant to products.
6. When both $\Delta H$ and $\Delta S$ is negative, $\Delta G$ can be either positive or negative depending on the temperature.
7. At low temperature, the reaction becomes spontaneous and at high temperatures, the reaction becomes non-spontaneous.