### heat/energy

```To cause the state of matter to
change….
Heat/Energy needs to be…..
Heat that is removed is….
Exothermic
surroundings
system
heat
Endothermic
surroundings
system
heat
Endothermic versus Exothermic Example WS
Scenario
Endo or Exo? Explain
1
Your car burns gasoline as you drive
from home to school
Exothermic – “burning “
releases energy
2
the oven.
Endothermic – “baking”
absorbs energy
3
The ice melts in your glass of water.
Endothermic – “melting”
absorbs energy
4
Sodium and chlorine combine in an
explosive reaction to form table salt.
Exothermic – “explosive” shows
releasing energy
5
Barry Balloon lights his candles to get
his hot air balloon to fly.
Exothermic – “lighting” candles
releases energy
6.
Water freezes on the pavement and
Exothermic – “freezing”
releases energy
Endothermic versus Exothermic Example WS
Scenario
Endo or Exo? Explain
7.
Mom puts a pot of water on the
stove and the water begins to boil
Endothermic – “boiling”
absorbs energy
8.
Water condenses on the side of your
Exothermic - “condensation”
releases energy
9.
A glass of water left out overnight
evaporates.
Endothermic – “evaporation”
absorbs energy
10.
A plant carries out photosynthesis.
Endothermic“photosynthesis” absorbs
energy
11.
A tree grows.
Endothermic – “growing”
absorbs energy
12.
Sally gets really sweaty as she runs.
Then she stops running and the
sweat evaporates.
(Hint: A 2-part question)
Exothermic- “sweat” giving
off energy
Endothermic – “evaporation”
absorbs energy
Changes in State
Liquid  gas : Vaporization
To cause this change….
Hvap
surroundings
system
heat
Heat of vaporization
Gas  liquid : Condensation
To cause this change….
heat/energy needs to be removed
Hcond
surroundings
system
heat
Heat of condensation
Vaporization Point
(the temperature a liquid turns into a gas)
=
Condensation Point
(the temperature a gas turns into a liquid)
Melting/Fusion is..
the vibrations in a solid are strong enough to…
overcome attractions that keep solid atoms together
Solid  liquid: Fusion
To cause this change….
Hfus
surroundings
system
heat
Heat of fusion
Liquid  Solid: Solidification
To cause this change….
heat/energy needs to be removed
Hsolid
surroundings
system
heat
Heat of solidification
Melting (Fusion) Point
(the temperature a solid turns into a liquid)
=
Solidification Point
(the temperature a liquid turns into a solid)
Relationships
Endothermic
Exothermic
+Hvap = - Hcond
-
+Hfus= Hsolid
Energy in Physical Changes
Heat of Physical Changes Table
On your note sheet: types of thermochem problems
Substance
Melting
point
°C
Heat of
fusion
(kJ/kg)
Helium
-269.65
5.23
Hydrogen
-259.31
58.6
Nitrogen
-209.97
25.5
Oxygen
-218.79
Ethyl
alcohol
Heat of
solidification
(kJ/kg)
Heat of
condensation
(kJ/kg)
Boiling
point
°C
Heat of
vaporization
(kJ/kg)
-268.93
20.9
-252.89
452
-195.81
201
13.8
-5.23
-58.6
-25.5
-13.8
-182.97
213
-20.9
-452
-201
-213
-114
104.2
-104.2
78
854
-854
Mercury
-39
11.8
357
272
Water
0.00
334
100.00
2256
Sulfur
119
38.1
444.60
326
327.3
24.5
1750
871
Antimony
630.50
165
1440
561
Silver
960.80
88.3
2193
2336
Gold
1063.00
64.5
2660
1578
1083
134
-11.8
-334
-38.1
-24.5
-165
-88.3
-64.5
-134
2567
5069
-272
-2256
-326
-871
-561
-2336
-1578
-5069
Copper
When doing word problems….
1. Find the question word: determine what you
are looking for. WANT
2. What #s did the problem give you
GIVEN
3. If only one # always start grid with that #
4. If Multiple #’s you NEED a formula
Ex.1 How much heat is absorbed when 24.8 g
water is evaporated?
Ex 2 How much heat is transferred when 400
grams of mercury (Hg) is vaporized?
Ex 3 If 300 kJ of heat is available, how much
copper can be melted?
Ex 4 How much heat is transferred when 100
grams of ethyl alcohol condenses?
Sublimation
SOLID skips liquid stage goes straight
into GAS stage
Demo 1: Sublimation
You forgot your glass of water outside.
The next time you are outside, you
realize your glass is empty. What
happened?
Evaporation Vs Boiling
• Both are Vaporization
• Both allow liquid turn into a gas
BUT….
• Evaporation is NOT Boiling
Evaporation
In an open container
Δ occurs @ the surface
Evaporation
It’s a cooling process
Evaporation
Explain how the following description is
an analogy for evaporative cooling:
If the fastest runner is removed from a
race, the resulting average speed of the
runners that remain will be lower.
Boiling
Liquid has enough HEAT/ENERGY
to
overcome the External Pressure
Vapor Pressure = External Pressure
to make something boil
Or
the EXTERNAL pressure is changed
Boiling
Affect of  Temp on Contained Liquid
 KE of particles
 particle collisions
 VP
This why a tea kettle whistles
Vacuum
no gas particles = no collisions
=
NO PRESSURE
Demo 2: Boiling
Atmospheric Pressure
Gas particles in Air colliding in earth’s atmosphere
More gas particles =
More collisions=
More pressure
Elevation and Atmospheric Pressure
↑ Elevation = ↓ Atmospheric Pressure
b/c
less gas particles =less collisions =  P
Sea Level more gas particles = more P
Elevation and BP
Pressure Cooker
Creates a High External Pressure
 a bubble of vapor can’t form unless KE= T
 BP is = hotter liquid= shorter cooking time
```