CH 2.1: Weak Interactions in Aqueous Systems

Why can polar molecules dissolve?

The water-water interactions are replaced with more favorable water-solute interactions

What are the weak interactions?

Hydrogen bonds, ionic, hydrophobic, and van der Waals

Why does water have a great internal cohesion?

• High melting point

• High boiling point

• High heat of vaporization

What is an hydrogen bond?

An electrostatic attraction between an oxygen of one water molecule and an hydrogen of another hydrogen molecule

Why do hydrogen bonds form?

Oxygen is more electronegative than hydrogen, pulling the lone pairs closer to the oxygen. This creates a dipole: partial positive on hydrogen and partial negative on oxygen. Allowing an electrostatic attraction between oxygen and hydrogens of different water molecules

What is bond dissociation energy?

The energy required to break a bond

What is the bond dissociation energy of a hydrogen bond?

23 kj/mol

What is thermal energy?

Kinetic energy of motion of individual atoms and molecules

What does flickering clusters of water mean?

Hydrogen bonds break and reform very quickly (0.1 picoseconds)

What is the cause of the crystal lattice structure of water when frozen?

The molecules are moving very slowly (vibrate) and can form hydrogen bonds with four other water molecules, which is the max hydrogen bonds it can form.

How hydrogen bonds can water make at room temperature and standard pressure?

3.4 water molecules

Why is the melting temperature of water so high?

It takes a lot of energy to break the crystal lattice structure

When ice melts and gas forms does entropy increase or decrease?

Increase: goes from highly ordered to high randomness

Why does melting and evaporation occur spontaneously at room temperature?

Entropy outweighs hydrogen bonds