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

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 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