Answer 1:
Heat, which is a form of energy that flows from
high to low
temperature, is measured with a calorimeter.
To understand how a calorimeter works, you need to
know about heat capacity:
Heat capacity is the amount of heat energy needed
to change the
temperature of a certain amount of a substance by
a given amount. The
units are energy per mass and temperature (eg.
Joules/(g•°C). For
example, the heat capacity of water is 4.19
J/(g•°C). That means it
takes 4.19 Joules of energy to raise the
temperature of 1 g of water
by 1°C. You could also think of this as 1 g of
water stores 4.19 J for
every 1°C increase in its temperature.
There are many types of calorimeters, but the
general idea behind how
they work is that if you know the heat capacities
and quantities of
the substances in and around the calorimeter, you
can measure a change
in temperature, and calculate how much heat energy
there is.
Let's say you want to measure the heat produced by
a reaction. Your
calorimeter would be an insulating container,
filled with water, with
a second container in the water. You would place
your reactants in the
closed inner container. You would measure the
temperature of the
system and then start the reaction. After the
reaction is complete,
you measure the temperature again. If you know the
heat capacities of
the water and container, you can calculate how
much heat was produced.
For an ever more accurate calculation, you would
also need to know the
heat capacities of the reactants and products
Now, you might be curious as to how we would
measure the heat
capacities of all of those things in the first
place. To do that, you
need a different type of calorimetry. Let's say
this time you want to
measure the heat capacity of water. You would put
the water in an
insulating container with an electrical heating
element and a
thermometer. The electrical heating element works
by resistive
heating, so you can calculate how much heat you
are adding by
measuring how much current you are using. Then you
measure how much
the temperature of the water changes. From this
information (amount of
water, amount of heat (current) added, and
temperature change), you
can calculate the heat capacity (4.19 J/(g•°C)) of
the water. Of
course, you can do this for substances other than
water as well.
Many calorimeter designs exist but they all
operate on similar
principles to what I have described here. They
often have more complex
components to decrease the amount of heat lost to
the surroundings,
make the calculations of heat simpler, accommodate
reactions involving
liquids and gases, or use an advanced method for
more accurate
measurements.
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