A nonspontaneous chemical reaction or physical change is one that requires assistance to keep going. We cannot predict the rate of a chemical reaction by determining whether the reaction is spontaneous or nonspontaneous. Some spontaneous reactions are fast, others are slow. Please do not block ads on this website.
The enthalpy of a chemical system will be minimised when the enthalpy of the products H products is less than the enthalpy of the reactants H reactants , that is:.
Heat energy is a product of the exothermic reaction. A reaction is therefore more likely to be driven in the forward direction, be spontaneous in the forward direction, if it is an exothermic reaction that is, if it releases heat energy. The second law of thermodynamics tells us that the entropy of the universe is constantly increasing.
Therefore chemical reactions should proceed spontaneously in the direction that increases the entropy of the system. If there is an increase in entropy then the entropy of the products S products is greater than the entropy of the reactants S reactants :. A reaction is most likely to be spontaneous if it is exothermic AND there is an increase in entropy of the system. Play the game now! This combustion reaction releases kJ of heat energy per mole of ethanol consumed in the reaction. Related questions How is Hess's law applied in calculating enthalpy?
How do you compute Hess's law calculations? How do you draw a Hess's law diagram? What does Hess's law say about the enthalpy of a reaction? Why isn't Hess's law helpful to calculate the heat of reaction involved in converting a diamond Remember that, at equilibrium:.
Using the appendix table of standard thermodynamic quantities, determine the temperature at which the following process is at equilibrium:. How does the value you calculated compare to the boiling point of chloroform given in the literature? At equilibrium:. The literature boiling point of chloroform is Skip to main content. Chapter Chemical Thermodynamics. Search for:.
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