What happens to the particles of a solid if we keep on heating it?

YEAR 8

UNIT 8I - HEATING & COOLING

WEEK 7

7.1 What happens to the particles of a SOLID if we keep on heating it ?(10 mins)

DEMO : kinetic cube – bigger and bigger vibrations as it gets hotter and hotter,

UNTIL bonds start to WEAKEN (some BREAK) : melting begins.

When will it all be melted ? : not until ALL the bonds have been weakened.

7.2 What happens to particles of a LIQUID if we keep on heating it ? (5 mins)

When boiling point is reached, some bonds break completely freeing particles.

When will the liquid all become gas ? Not until ALL the bonds have been broken, then ALL the particles are free.

7.3 What happens to the temperature of a substance whilst it is freezing? (40 mins)

Class expt. + Run demo. With SM sensor & data logger on large screen

Apparatus:

Stopwatch, thermometer, 250ml beaker, boiling tube containing stearic acid, safety specs.

Method:

Collect a boiling tube of stearic acid from the water bath.
Take the temperature of the stearic acid and start the stopwatch.
Return to your working area and place the boiling tube in the empty beaker.
Stir GENTLY and continuously until the stearic acid solidifies.
Take the temperature every minute and record your results in a table.
Continue taking readings until 5 minutes after all the acid has completely solidified.

Results:

Homework :

1. Plot a graph of temperature AGAINST time (fully labelled, with units, on A4 graph paper).

2. Mark on the graph

• The section which represents liquid (label it 'LIQUID').

• The “plateau” section where the temperature stops falling AND the liquid starts to solidify

(label it 'LIQUID + SOLID').

• The half-way point along the plateau where we have half liquid and half solid.

• Beyond the end of the plateau ALL the liquid has solidified AND the temperature starts to fall again

(Label it 'SOLID').

Conclusions:

At the start the liquid loses heat to the surroundings.
On the plateau it is still losing heat but it is also SOLIDIFYING.
During this time the particles are bonding together.
It's temperature cannot fall until ALL liquid has solidified, all bonds are formed (extra heat energy is coming out of it during this time as the molecules come closer together and form bonds).