SSS 1: Heat energy (II)

Real Cubic Expansivity (γ_r)

Real (absolute) cubic expansivity is defined as the actual volume per unit volume per degree rise in temperature when the expansion of the vessel is taken into consideration.

Apparent Cubic Expansivity (γ_a)

Apparent cubic expansivity is the increase in volume per unit volume per degree rise in temperature when the expansion of the vessel is not considered.

Real Cubic Expansivity (γ_r) = Apparent Cubic expansivity (γ_a)

+ cubic expansivity of the container (γ_c).

                           γ_r = γ_a + γ_c

 

Example

1. A density glass bottle contains 42.02g  of a liquid at 0^oc and 44.25g at 50^oc. Calculate the real cubic expansivity. (Linear expansivity of glass, 

α = 1.0 x 10^-5k^-1)

                           Solution 

2. A relative density bottle of volume 50cm³ is completely filled with a liquid a 30^oc. It is then heated to 80^oc such that 0.75cm³ of the liquid is expelled. Calculate the apparent cubic expansivity of liquid.

                            Solution

3. A metal cube of linear expansivity (α) is heated through a temperature rise of (t). If the initial volume of the cube is (v). What is the increase in volume of the cube.

                      Solution

Variation of density with temperature

ANOMALOUS EXPANSION OF WATER

The anomalous expansion of water is an abnormal property of water during freezing whereby water expand instead of contracting when the temperature goes from 4^oc to 0^oc and becomes less dense. Water has a maximum density at 4^oc.

Reason for Anomalous Expansion of Water

At 0^oc, the water molecules lose their open structure and becomes more hydrogen bounded. The intermolecular force between water molecules are reduced. As a result, density rises from 0^oc to 4^oc.

Anomalous behaviour of water can be illustrated using Hope’s experiment.

                 CHANGE OF STATE

1.       Fusion (Melting)

Fusion is the process whereby a substance changes from a solid state to a liquid state when heat is applied to it.

         Melting Point

Melting (Fusion) point is the temperature at which a substance changes from a solid state to a liquid state.

2.       Freezing

Freezing is the process whereby a substance changes from a liquid state to a solid state.

         Freezing Point

Freezing point is the temperature at which freezing occurs.

3.       Vapourization

Vapourization is the process by which a substance changes from a liquid to gaseous state when heat is applied to it.

           Boiling Point

Boiling point is the temperature at which vapourization occurs.

4.       Evaporation

Evaporation is the process whereby a liquid turn into vapour below its boiling point.

5.       Condensation

Condensation is the process in which a gaseous substance is converted into its liquid state.

Examples of condensation include:

i.        Morning dew on the grasses

ii.       Water droplets on the outer surface of cold drink bottle

iii.      Foggy car windows

 

                 Assignment

Discuss the experiment on how to determine the anomalous expansion of water. (Hope’s experiment)