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
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