To cause the state of matter to change…. Heat/Energy needs to be….. added or removed
Mar 23, 2016
To cause the state of matter to change….
Heat/Energy needs to be…..
added or removed
Heat that is removed is….
Exothermic
system heat
surroundings
Heat that is added is….
Endothermicsystem heat
surroundings
Endothermic versus Exothermic Example WS
Scenario Endo or Exo? Explain
1 Your car burns gasoline as you drivefrom home to school
Exothermic – “burning “ releases energy
2 Jerry is baking homemade bread inthe oven.
Endothermic – “baking” absorbs energy
3 The ice melts in your glass of water. Endothermic – “melting” absorbs energy
4 Sodium and chlorine combine in anexplosive reaction to form table salt.
Exothermic – “explosive” showsreleasing energy
5 Barry Balloon lights his candles to gethis hot air balloon to fly.
Exothermic – “lighting” candlesreleases energy
6. Water freezes on the pavement andthe roads become icy.
Exothermic – “freezing” releases energy
Endothermic versus Exothermic Example WSScenario Endo or Exo? Explain
7. Mom puts a pot of water on thestove and the water begins to boil
Endothermic – “boiling” absorbs energy
8. Water condenses on the side of yourglass of cold lemonade.
Exothermic - “condensation” releases energy
9. A glass of water left out overnightevaporates.
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 thesweat evaporates.(Hint: A 2-part question)
Exothermic- “sweat” giving off energyEndothermic – “evaporation” absorbs energy
Changes in State
Liquid gas : Vaporization
To cause this change…. heat/energy needs to be added
system heat
surroundings Hvap
Heat of vaporization
To cause this change…. heat/energy needs to be removed
Gas liquid : Condensation
system heat
surroundings Hcond
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…. heat/energy needs to be added
system heat
surroundings
Hfu
s
Heat of fusion
Liquid Solid: Solidification
To cause this change…. heat/energy needs to be removed
system heat
surroundings
Hsol
id
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
+Hvap = - Hcond
+Hfus = - Hsolid
Endothermic Exothermic
Energy in Physical Changes
Heat of Physical Changes TableOn your note sheet: types of thermochem problems
SubstanceMelting
point°C
Heat of fusion(kJ/kg)
Heat of solidification
(kJ/kg) Boiling point
°C
Heat of vaporization
(kJ/kg)
Heat of condensation
(kJ/kg)
Helium -269.65 5.23 -5.23 -268.93 20.9 -20.9Hydrogen -259.31 58.6 -58.6 -252.89 452 -452Nitrogen -209.97 25.5 -25.5 -195.81 201 -201Oxygen -218.79 13.8 -13.8 -182.97 213 -213Ethyl alcohol -114 104.2 -104.2 78 854 -854
Mercury -39 11.8 -11.8 357 272 -272Water 0.00 334 -334 100.00 2256 -2256Sulfur 119 38.1 -38.1 444.60 326 -326Lead 327.3 24.5 -24.5 1750 871 -871Antimony 630.50 165 -165 1440 561 -561Silver 960.80 88.3 -88.3 2193 2336 -2336Gold 1063.00 64.5 -64.5 2660 1578 -1578Copper 1083 134 -134 2567 5069 -5069
When doing word problems….
1. Find the question word: determine what you are looking for. WANT
2. What #s did the problem give you GIVEN3. 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 containerΔ occurs @ the surface
EvaporationIt’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
Energy/Heat is added Or
the EXTERNAL pressure is changed
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 PressureGas 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