this word is endothermic so endothermic
is a reaction or a process that actually
takes in energy in the form of heat from
its surrounding area when you have
chemical reactions some chemical
reactions need heat to make them go the
products of the reaction have more
energy in them than your starting
materials it will actually suck in this
heat energy and it will make it very
very cold so we'll actually see
something that becomes very cold either
you can measure it with a thermometer or
you can actually feel it with your hands
getting colder and colder chemists have
quite a limited view of the world when
they're thinking about
reactions they just think about their
flask and what's going on in their flask
and all they're interested in is whether
heat is Flowing out or heat is flowing
in and if a reaction is
endothermic it needs heat to make it go
so heat has to flow in if you want to
keep the temperature the same if you
don't mind about the temperature the
endothermic reaction will just make
things get cold but because reactions go
slower when they're cold usually you
heat it up to keep the temperature
constant so we're actually going to
demonstrate it using a chemical uh
called ammonium nitrate we're actually
going to set it up connect a thermac
couple um to read how cold it's going to
get so at the moment it's reading well
how cold this lab is at the moment so
we'll see what happens so this stuff is
cooked in here so oh it's a heavy
jar what it means in effect is that you
are breaking strong chemical bonds and
making weak ones and very often we want
to do that the harbor process where you
take nitrogen from the air and make
ammonia for fertilizer is a very good
example of an endothermic reaction you
have to put in more heat than you get by
formation of the chemical bonds okay the
thermac couple is inside right in the
middle of the beacon now I'm just going
to push that down give us a even layer
and the thermac couple is reading the
temperature inside the beaker which is
pretty much the same as out here in the
lab so what's going to happen is I'm
going to add some water to this the
ammonium nitrate is going to dissolve in
the water and what will happen is the
ammonium part and the nitrate part they
split apart and become Sol a solution so
they become ions in solution so I've got
the water here distill water it will go
in and we can actually see what
happens the reaction can be something
quite boring like something
dissolving what you do is you break the
strong forces between the ions in the
Crystal and replace them with the rather
weaker forces between the water
molecules and the ions
so some things when you dissolve them in
water get really cold so you can see
that immediately we get the process of
of you know it being endothermic so what
that means is that it's gone from being
about 15° C to now minus 15- 16 so
although it's a 16.3 here there's
actually a minus symbol there so that's
how cold it's got and in fact if I touch
this I can feel just how cold it's
become the endothermic mixing of night
acid and Ice was used by Fahrenheit to
find zero or to Define zero on his
temperature scale he wanted to get
something was really really cold so he
mixed concentrated nitric acid with snow
and the temperature went straight down
to the temperature which he called 0° F
it's just like as if I'm getting
something a bag of peas or whatever out
of the freezer so it's it's really as
old as that so it's only been a few
seconds and already it's gone from being
at room temperature right the way down
to- 16