Question

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Answer 1

Physical change:

• A substance that undergoes a physical change such as in shape, size, colour, state, or appearance is called a physical change.
• The chemical properties of the substance won't change.
• Physical change is temporary and no new products are formed.

Chemical change

• A substance that undergoes a change in its chemical properties is called a chemical change.
• The chemical changes are permanent irreversible changes and a new product is formed.

Fermentation:

• Fermentation occurs in an anaerobic environment that is in the absence of air, where sugar changes to alcohol, which is not available when the grapes are on the tree.

$\underset{\mathrm{Glucose}}{{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\left(\mathrm{aq}\right)}\stackrel{\mathrm{yeast}}{\to }\underset{\mathrm{Ethanol}}{2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{aq}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{2{\mathrm{CO}}_2\left(\mathrm{g}\right)}$

• Fermentation is usually a slower process and irreversible process, which means it is a chemical change.

Hence, the fermentation of grapes is a chemical change.