What kind of things get the hottest in summer?
Phase Change
notes
water can absorb a lot of energy. But
how much?
Let's start with 1 gram of ice at -50 °C
and follow along as we heat it up.
Phase Change
As we heat the ice from -50 °C to 0 °C,
we have to use 2.108 Joules for each
degree.
Note that this specific heat is not 4.186.
Ice has a different specific heat!
Phase Change
As we keep adding energy, our ice stops
warming up. Instead, all the energy goes
into melting the ice into liquid water.
We will have to add 80 Joules to melt
our 1 gram of ice. We call this special
energy barrier the “heat of fusion”.
Phase Change
Next we start heating up our liquid
water. As we heat it from 0 °C to 100 °C,
we have to use 4.186 Joules for each
degree.
In total, we use 420 Joules to heat up
our water to boiling.
Phase Change
Once again, we hit another barrier. As
we add more energy to our hot water, it
stops heating up and instead begins
turning to steam.
We have to add a whopping 2255
Joules to turn our water into steam!
That's more energy than it would take to
get it from absolute zero to this point.
We call this the “heat of vaporization”.
Phase Change
In our last phase, we heat up our steam.
It takes 1.996 Joules of energy for
each degree we want to heat it up.
Vocabulary
vocab
Heat of
Fusion
The extra energy you have to add
to turn a solid into a liquid
Heat of
Vaporization
The extra energy you have to add
to turn a liquid into a gas
Vocabulary
Specific Heat
vocab
A measure of how easy or hard it is
for an object to absorb and hold heat.
The specific heat of water is 4.186 J/goC
This means it takes a little over 4 J to
raise the temp of 1 gram of water 1oC
Equation
Specific Heat
equation
Q = m * c * ΔT
Q: How much energy it takes to heat
something up. Measured in Joules
m: Mass of the object in grams.
c: Specific heat. How well the object
absorbs heat.
ΔT: Change in temperature. Measured
in °C.
We use this equation to find out how
much energy it takes to heat
something up.
Phase Change
We can put this all together in a graph.
Energy for phase-changing 1gram of water
2255 J
Heat of Vaporization
4.186 J/goC
80J
Heat of fusion
2.108J/goC
1.996J/goC
Calculate the amount of energy needed to
raise 1 gram of ice at 50oC to steam at 110oC
Calculate the energy given up when 2 grams of
steam at 105oC is cooled to ice at -30oC
Phase Change & Specific Heat
classwork
Let’s practice some ideas related to phase change
and specific heat.
Do the following problems:
Page 338 Review: 26, 27
Page 340 Exercises: 24, 25
Page 302 Review: 15, 16
Page 303 Exercises: 15, 18
Exit Question #40
2.5b
Specific Heat is a measurement of...
a. The total energy inside something
b. How hot something can get before it emits light
c. How big an object is compared to how hot it gets
before melting
d. How much energy an object can absorb before its
temperature rises
e. The specific amount of heat already in something
f. Whether something is solid, liquid, and gas