Fired Up!
Energy Changes
• Describe some of the changes you observed during
today’s demos
• What common features did you notice?
• Is energy associated with these reactions? Explain.
Energy is a measure of how much you can move
or change something.
• Give examples of how you use the word energy in your daily
life.
• In your experience, how is energy related to change and
motion?
• How would you define energy?
• Is energy a substance?
What reactions are sources of heat?
• Changes in __________________________________.
• Reactions of elements and compounds with _________ (or
oxygen containing compounds like KClO3 typically produce
products that are ____________________ the reactants.
• Fire, or combustion, is a type of reaction that __________
_________________ in the form of flames, heat, and light.
• Energy is a measure of the_________involved in moving or
changing something.
Forms of Energy
________
________
______
________
__________
__________
________
________
_____
______
______
_______
Classify the Energy into
Potential
Kinetic
How a monkey uses energy conversion
to leap from tree to tree
Energy conversion steps in hair dryer operation
Power plant furnace
(thermal energy)
Generator turbine
(mechanical energy)
Fossil fuel
(potential energy)
Electrical lines
Hair dryer
(mechanical, thermal, (electrical energy)
sound energy)
Not So Hot: Exothermic and
Endothermic
Chem Catalyst
• Name at least 3 ways you can warm yourself on a cold day.
• What do you think is the source of the heat in a hand
warmer?
• Why does rubbing your hands together make you warmer?
• A toe warmer will work for up to 6 hours if it is in your shoe,
but it won’t last as long out of your shoe. Explain.
Not So Hot
Observe energy changes that occur during a chemical reaction
•
Follow these instructions
1.
2.
3.
4.
•
•
•
Measure initial temperature
Conduct reaction
Measure highest/lowest temperature reached
Calculate change in temperature = T = Tfinal - Tinitial
Station 1. HCl(aq) + NaHCO3(aq)
[mix 50:50]
Station 2. CaCl2 (s) + H2O(l)
[start with ½ test tube water, add scoop of CaCl2(s)]
Station 3. NH4Cl(s) + H2O(l)
[start with ½ test tube water, add scoop of CaCl2(s)]
Not So Hot
• What did you observe at the three stations?
• What did the thermometer tell you in each case?
Check-In
You have water at 25C. You dissolve ammonium acetate,
NH4C2H3O2, in the water and find that the temperature
decreases to 15 C.
1. Is heat transferring from the solution to the
surroundings, or from the surroundings to the
solution?
2. Is the process exothermic or endothermic?
Unit V • Investigation I
ChemCatalyst
1. Imagine you are sitting near a campfire. You feel warm.
Explain how you think the warmth gets from the burning
wood to your body.
2. The fire goes out. The next morning, you find ashes that
are the same temperature as the air. Explain why the
ashes are no longer hot.
3. Why do you think the campfire eventually burns out?
Unit V • Investigation I
Wrap-Up
– Heat is a ______________________________
___________________________________(not a noun!)
– The direction of energy transfer is ____________ at
________________ to an object at ______ temperature.
• There is no such thing as “____________.” Cold is the experience
of ___________________________ from your body.
– _____________ is transferred when _________________
molecules ______________________ moving molecules.
– Thermal equilibrium: ____________________________
_______________________________________________
_______________________________________________
Check-In
• Imagine a thermometer is placed in a beaker of
water and the temperature is noted. An ice cube
is dropped into the water and after ten minutes
the temperature is noted again.
– What will you observe?
– What is the direction of heat transfer?
Heat vs. Temperature
Which will melt more of a snowman, a cup of coffee at 90oC, or a
bathtub of water at 20oC? Explain.
Three Main Ways Heat is Transferred
Conduction __________________________________________
_____________________________________________________
Convection ___________________________________________
_____________________________________________________
Radiation: ___________________________________________
_____________________________________________________
System vs. Surroundings
Surroundings =
thermometer, flask, and
the rest of the universe.
System
System: _______________________________________________
_______________________________________________________
Surroundings: __________________________________________
_______________________________________________________
Exothermic and Endothermic
• Heat: _____________________________________
____________________________________________
• Exothermic process: ________________________
__________________________________________
• Endothermic process: _______________________
____________________________________________
FRHs heat MREs quickly, without fire
19
GI’s MRE
20
MREs have changed over the years
1980s MRE
–
–
–
–
–
–
–
–
–
Pork Patty
Ham and chicken loaf
Beef slices in BBQ sauce
Beef and Mushroom
Beef stew
Frankfurters with beans
Turkey diced with gravy
Chicken a la King
Meatballs & BBQ sauce
1980s MRE
•
•
•
•
•
•
•
•
•
BBQ Pork rib
Beef ravioli
Cheese & vegetable omelet
Chicken breast filet
Chicken fajita
Chicken with salsa
Hamburger patty
Beef stew
Chili with macaroni
Some of the early MRE entrées were not very palatable, earning them
the nicknames "Mr. E" (mystery),[3] "Meals Rejected by Everyone",[4]
"Meals, Rarely Edible",[5] "Meals Rejected by the Enemy", "Meals
Refusing to Excrete", and even "Meals Rejected by Ethiopians"[6] in
reference to a country that was gripped by famine at the time. Some
meals got their own nicknames. For example, the frankfurters, which
came sealed in pouches of four, were referred to as "the four fingers of
death."
21
FRH exothermic reaction:
Mg + H2O  Mg(OH)2 + H2 + energy
WARNING:
Vapors released by activated heater contain hydrogen, a
flammable gas. Do not place an open flame in the vapor.
Government test: ignite MRE vapors with a match
22
Cargo fire during shipment of MREs in March 2001
FAA report: “Limiting Oxygen Concentration Required to Inert Jet Fuel
Vapors Existing at Reduced Fuel Tank Pressures—Final Phase,” FAA
Report DOT/FAA/AR-04/8, August 2004.
23
Endothermic reactions absorb energy from the
surroundings
NH4Cl(s) + H2O  NH4Cl(aq)
A water in a copper pot is placed on a burner.
The pot soon becomes too hot to touch, but
the water is only lukewarm. Why?
Copper has a ___specific heat
capacity – it only takes a little
energy to heat it:
1 g Cu
at 25°C
Water has a_____specific heat
capacity – it takes a lot of energy
to heat it:
+0.09 calories
heat
+ 1.00 calories
heat
1 g Cu
at 26°C
1 g H2O
at 26oC
1 g H2O
at 25oC
The specific heat capacity ____________________________________
___________________________________________________________
The high specific heat of H2O protects firewalkers
Unit V • Investigation I
Calorimetry
Imagine that you heat water over
a campfire.
1. How can you tell that energy is
transferred to the water?
2. How could you measure the amount
of energy transferred to the water?
3. How could you measure the amount
of energy one stick transfers to the
water when it burns?
What units do we use to measure energy?
What units measure the energy contained in these items?
• Energy content is measured in units of calories or joules
Unit V • Investigation I
Measuring Energy Changes
• 1 calorie = amount of energy (heat) required to raise the
temperature of 1 g water by 1°C
• 1 calorie = 4.184 J (joules); J is SI unit
 1 food Calorie = 1000 calories = 1 kcal
• How much energy (heat) in joules is required to raise the
temperature of 7.40 g water from 29.0 °C to 46.0 °C?
Unit V • Investigation I
q = m C T
•
•
•
•
q = thermal energy (heat) absorbed/released
m = mass that heats up
T = change in temperature, in °C
C = specific heat capacity= energy needed to raise 1.0 g of a
substance by 1°C
Cwater
= 1.0 cal/g°C
Caluminum = 0.2 cal/g°C
• Which takes less energy to heat, water or Al?
Unit V • Investigation I
Calculations with Specific Heat Capacity
(aka Specific Heat)
heat gained
or lost
Q
=
mass
in grams
change in
temp, °C
specific
heat
= (m) (T) (s)
Conservation of Energy: heat gained = heat lost
What is the final temp when 21.5 g iron at 100.0°C is dropped
into an insulated container with 132 g water at 20.0°C? (The
heat capacity of iron is 0.449 J/g°C)
Unit V • Investigation I
Combustion of Cheetos:
C24H50O25+ 24 O2  24 CO2 + 25 H2O + energy
We will quantify the energy
released as heat by measuring
the increase in temperature of
100 mL of water
Unit V • Investigation I
A bomb calorimeter measures the energy released in a
reaction
Why do Florida citrus growers spray water on their trees to
prevent frost damage? Why does hot apple pie filling burn your
mouth, but the crust doesn’t?
Unit V • Investigation I
Total potential energy ruler
What happens when your body “burns”
food?
maintenance
growth
body heat
CO2 + 2H2O
Kaboom ! Explosions are exothermic!
4 C3H5N3O9
6N2 + 12CO2 + 10H2O + O2 + energy
Many chemical explosives (e.g. ammonium nitrate,
TNT, nitroglycerin) contain nitro groups (NO2) which
decompose to give more stable products
Energy is stored in chemical bonds: the
shuttle uses H2 as its fuel
2H2 + O2  2H2O + energy
Ostrich egg:
Total potential energy ruler
Exothermic reaction: products contain less
stored (potential) energy than reactants
2H2 + O2
difference in energy
exits as heat/light
2H2O
Total potential energy ruler
Combustion of hydrocarbons is exothermic because the
products store less energy than the reactants
CH4 + 2O2
difference in energy
expelled as heat+light
CO2 + 2H2O
Combustion of methane is exothermic because Step 2 (bond
formation) releases more energy than Step 1 (bond breaking)
requires.
Combustion of fossil fuels for energy
• What are fossil fuels and where did they come from?
• Fossil fuels include coal, petroleum, natural gas
– Probably from living matter dating back 500 million years
– No detectable fossil fuel being produced now, so these are
non-renewable resources
• What are fossil fuels made of?
• Fossil fuels are mostly hydrocarbons
• What are the harmful effects of burning fossil fuels?
• Combustion of coal and petroleum products produces air
pollutants and heavy metal containing ash
– CO2 contributes to global warming
– NOx and SOx are air pollutants
– Particulates from diesel may contribute to asthma and
cancer