Question

In ethanol, $C_{2}H_{5}OH$, there are covalent bonds, hydrogen bonds and van der Waals' forces. Which bonds or forces are broken when ethanol is vaporized?

• A. Only hydrogen bonds
• B. Hydrogen bonds and van der Waals forces
• C. Covalent bonds and van der Waals' forces
• D. Covalent bonds and hydrogen bonds

Hint:

Physical changes break "inter"molecular forces; chemical changes break "intra"molecular (covalent/ionic) bonds.

Answer 1

The Correct Option is B

Step 1: Concept
Phase changes (like vaporization) involve overcoming intermolecular forces, not intramolecular (covalent) bonds.

Step 2: Identification of Forces
Ethanol molecules are held together in the liquid phase by hydrogen bonding (due to the -OH group) and London dispersion forces (van der Waals forces).

Step 3: Analysis of Vaporization
When ethanol turns into gas, the molecules separate from each other. This requires breaking the intermolecular attractions (hydrogen bonds and van der Waals forces) while keeping the $C_{2}H_{5}OH$ molecule intact.

Step 4: Conclusion
Vaporization breaks intermolecular forces but does not break covalent bonds. Final Answer: (B)