HEATING AND COOLING
When a substance is being
heated, you can tell that the
particles are absorbing
energy by measuring the
temperature. For example, as
you heat water, you should
see a temperature increase
as time goes by.
But something odd will
happen when the water
starts to boil….
The temperature will stop
increasing!
The heating curve
In this experiment, how long did it take for the water to start
boiling?
4 minutes
Why didn’t the
temperature of the water
increase after 4 minutes?
Temperature (oC)
water and steam
100
The energy was being
used to separate the
water molecules and turn
the liquid into a gas.
How long did it take for
all the water to turn into
steam?
12 minutes
18
4
16 Time (minutes)
The cooling curve for stearic acid
Temperature
How can we find the freezing
point of the acid?
(oC)
Look for where the temperature
stops changing. This is where the
substance is changing state.
60X
50
X
X
X
X
X
40
30
20
10
10
20
X
X
X
The freezing point of stearic acid
is 48oC.
If this experiment was continued,
the temperature would even off
around 20oC. Why?
When the solid stearic acid
cooled to room temperature, it
would not be able to cool any
more.
30
Time (minutes)
More cooling curves
Objects lose heat because they are warmer than their
surroundings. The hotter they are, in comparison to the
environment, the faster they will lose heat energy (at the beginning
anyway).
Look carefully
at the the
two cooling
graphs below
and
the following
Which
graph shows
of 500g
of answer
water and
which one
questions.
shows
the cooling of 500g of solid iron? Explain your answer.
temp
temp
A
100
100
75
75
50
50
25
25
time
B
B could not
represent the
cooling of water
since the starting
temperature is
above 100oC
time
More cooling curves
Objects lose heat because they are warmer than their
surroundings. The hotter they are, in comparison to the
environment, the faster they will lose heat energy (at the beginning
anyway).
Look carefully
attemperature
the two graphs
and
answer
the following
What
was room
on below
the day
this
experiment
was
questions.
done?
How did you find your answer?
temp
temp
A
100
100
75
75
50
50
25
25
time
B
Around 18oC. You
can tell since this
is where the graph
shows that the
objects
temperature
stopped changing.
time
More cooling curves
Objects lose heat because they are warmer than their
surroundings. The hotter they are, in comparison to the
environment, the faster they will lose heat energy (at the beginning
anyway).
Look carefully
the twocooled
graphsfaster?
below and
the tell?
following
Which
of theseatobjects
Howanswer
could you
Why
questions.
do
you think this one cooled faster?
The iron would
temp
temp
A
B
cool faster. You
can tell since the
100
100
slope of graph B is
steeper at the
75
75
start, than the
50
50
slope of graph A.
Iron cools faster
25
25
since it is a better
conductor.
time
time