Heating & Cooling Curves

D. Crowley, 2008

Heating & Cooling Curves

To understand heating and cooling curves

Wednesday, April 19, 2023

Temperature

The differences between solids, liquids and gases can be explained by the particle model: -

All substances are made up of particles (atoms, ions or molecules)

These particles are attracted to each other, some strongly and others weakly

These particles move around (i.e. have kinetickinetic energy)

The kinetic energy of particles increases with temperature

Temperature

Chemical & Physical

Watch the demo of chemical and physical changes…

Chemical Changes Physical Changes

New substances are formed No new substances are formed

Changes are usually permanent (irreversible)

Changes are usually not permanent (reversible)

States Of Matter

Ice melting into water is an example of a physical change

No new substances are formed during physical changes

At a cold enough temperature, even substances that are normally gases will become solid

At higher temperatures, solids change to become liquids or gases – as long as they don’t catch fire or decompose first

State Changes

Temperature Change

What happens to the temperature of a block of ice when a medium constant heat is applied to it?

Your task is to measure the temperatures of the ice as it is heated every 30 seconds (as well as noting the state of the water (solid, liquid, gas)): -

Time (seconds) Temperature (oC) State (solid / liquid / gas)

0

30

60

90

120

Etc…

Temperature Change

What happens to the temperature of stearic acid as it freezes?

Your task is to measure the temperatures of the stearic acid as it cools every 30 seconds (as well as noting the state of the stearic acid (solid, liquid, gas)): -

Time (seconds) Temperature (oC) State (solid / liquid / gas)

0

30

60

90

120

Etc…

Graphing

Plot your results on a graph

Water heating curve Stearic cooling curve

Heating Curves

Water heating curves

In general, the temperature goes up the longer the heating continues

The two horizontal flat parts to the graph occur when there is a change of state

The first change of state is melting - the temperature stays the same while a substance melts (0oC for water)

The second change of state is boiling - the temperature stays the same while a substance boils (100oC for water)

Cooling Curves

Stearic cooling curves

Cooling curves have horizontal flat parts where the state changes from gas to liquid, or from liquid to solid

Stearic acid has a melting point of about 69°C - the temperature stays the same as the liquid freezes

Change Of State

melting

freezing

solid liquid

boiling

condensing

liquid gas

tem

per

atu

re

time

solid

liquid

gas