A reaction will be spontaneous if it results in products that have

Lower potential energy and more randomness.

Explanation:

The spontaneous reaction is reaction in which chemical or physical change once started will continue taking place without any external help.

The change in enthaply and change in entropy are necessary for any chemical reaction to take place.

The enthaply is the measure of how much energy is measured or released during a chemical reaction.

The entropy is the measure of degree of disorder or randomness in a system.

The spontaneous reaction will proceed to minimise enthaply and maxime entropy.

Example:

The fire is exothermic reaction in which there is decerease in energy of systems as it is released in the system in form of heat. The product of fire is water vapour and gases such as carbon di oxide which means there is increase in entropy ie more molecules move randomly. The fire is spontaneous because there is decrease in energy and increase in entropy.

The second law of thermodynamics states that the entropy of universe is always increasing.

When the enthalpy change is negative ie exothermic reaction and entropy change is positive ie more randomness  the reaction is spontaneous.

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