1. Heating & Cooling Curves
D. Crowley, 2008

2. Heating & Cooling Curves
Sunday, May 12, 2019
Heating & Cooling Curves
To understand heating and cooling curves

3. 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 kinetic energy)
The kinetic energy of particles increases with temperature

4. Temperature

5. Chemical & Physical Chemical Changes Physical Changes
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)

6. 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

7. State Changes

8. State (solid / liquid / gas)
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) 30 60 90
120
Etc…

9. State (solid / liquid / gas)
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) 30 60 90
120
Etc…

10. Graphing Plot your results on a graph Water heating curve
Stearic cooling curve

11. 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)

12. 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

13. Change Of State gas boiling  temperature liquid melting  freezing
condensing
liquid  gas
gas
temperature
liquid
melting 
freezing
solid  liquid
solid
time