The Liquid Phase (College Board AP® Chemistry)

The Liquid Phase

• The particles in liquids are in constant random motion but are more tightly packed and have much less free space between them

• Unlike solids, the particles of liquids are able to move relative to one another, which means that liquids can flow

Liquid Phase

Diagram showing the arrangement and movement of particles that make up the liquid phase

• However, the lack of empty space between these particles makes them nearly incompressible

• Unlike gases, the size of liquid and solid particles compared to the distance between them cannot be ignored

  • Hence, they have fixed volume and there are no equations to describe the properties of liquid or solid state as they exist for gases

• The properties of liquids such as surface tension, viscosity, boiling point and vapor pressure are dependent on two main factors:

  • The nature and strength of the intermolecular forces between the particles of the liquid

  • Temperature

• Generally:

  • Surface tension — the energy required to increase the surface area of a liquid by a unit amount— increases with increasing strength of intermolecular force

  • Viscosity, which measures the resistance to the flow of liquids also increases with increasing intermolecular attraction but decreases with increasing temperature

  • Vapor pressure and boiling point of a liquid are dependent on the strength of the intermolecular force between the particles of the liquid

    • The stronger the intermolecular force, the lower the vapor pressure and the higher the boiling point of the liquid

Molar Volume in the Solid and Liquid Phase

• The solid and liquid phases for a particular substance typically have similar molar volume

  • This is because the distance between the particles of the substance in the solid phase is approximately the same as the distance between the particles in the liquid phase

  • Molar volume refers to the volume of one mole of a substance under standard conditions

Table of Molar volumes for metals in solid and liquid states

The table shows that the molar volumes of metals are similar in both solid and liquid states. The slight differences in value are due to the small space between the particles of the metals in the liquid state, allowing them to flow.