Question

Chemical reactions spontaneously occur when the free energy of the products is ___________ the free energy of the reactants.

Answer 1

lower

Step-by-step explanation:

For a spontaneous process, the standard Gibbs free energy change has to be less than zero:

∆G° < 0 → spontaneous

∆G° > 0 → non- spontaneous

∆G° = 0 → system is at equilibrium

For a negative change in standard Gibbs free energy, the Gibbs free energy of the products has to be lower than that of the reactants since Gibbs free energy change is the standard Gibbs free energy of products minus that of the reactants.

`\boxed{∆G= G°(products) -G°(reactants)}`

Mathematical derivation:

G°(products) -G°(reactants) < 0

G°(products) < G° (reactants)

✩ Note that in the image attached, the Gibbs free energy change is usually denoted by a single-headed arrow, from reactants to products.

What is free energy?

• the amount of energy available to do useful work
• it tells us the spontaneity of a chemical process

Standard state conditions

• You may have noticed the superscript ° after the letter G (which stands for Gibbs free energy), and this symbol denotes standard state.
• implies that the pressure of a gas is 1 atm
• implies that for a solute, its concentration is 1M

Spontaneity

• the ability of a reaction to occur without outside intervention
• For example, an ice melting in a cup of hot tea is a spontaneous process (i.e. the transfer of heat from a hotter object to a cooler object is spontaneous).