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

Fossil fuel(potential energy)

Power plant furnace(thermal energy) Generator turbine

(mechanical energy)

Electrical lines(electrical energy)

Hair dryer(mechanical, thermal,

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 HotObserve energy changes that occur during a chemical reaction

• Follow these instructions1. Measure initial temperature2. Conduct reaction3. Measure highest/lowest temperature reached4. 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?

Unit V • Investigation I

Check-InYou have water at 25C. 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?

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. TemperatureWhich 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: ___________________________________________________________________

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FRHs heat MREs quickly, without fire

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GI’s MRE

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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."

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FRH exothermic reaction: Mg + H2O Mg(OH)2 + H2 + energy

Government test: ignite MRE vapors with a match

Vapors released by activated heater contain hydrogen, a flammable gas. Do not place an open flame in the vapor.WARNING:

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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.

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?

1 g Cu at 25°C

+0.09 calories heat

1 g Cu at 26°C

1 g H2O at 25oC

+ 1.00 calories heat

1 g H2O at 26oC

The specific heat capacity _______________________________________________________________________________________________

Copper has a ___specific heat capacity – it only takes a little energy to heat it:

Water has a_____specific heat capacity – it takes a lot of energy to heat it:

Unit V • Investigation I

The high specific heat of H2O protects firewalkers

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?

Unit V • Investigation I

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 unit1 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

massin grams

change intemp, °C

specificheat=

Q = (m) (T) (s)

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)

Conservation of Energy: heat gained = heat lost

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

A bomb calorimeter measures the energy released in a reaction

Unit V • Investigation I

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?

What happens when your body “burns” food?

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CO2 + 2H2O

growth

body heat

maintenance

Kaboom ! Explosions are exothermic!

Many chemical explosives (e.g. ammonium nitrate, TNT, nitroglycerin) contain nitro groups (NO2) which decompose to give more stable products

4 C3H5N3O9

6N2 + 12CO2 + 10H2O + O2 + energy

Energy is stored in chemical bonds: the shuttle uses H2 as its fuel

2H2 + O2 2H2O + energy

Ostrich egg:

othermic reaction: products contain less stored (potential) energy than

reactants

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2H2 + O2

2H2O

difference in energy its as heat/light

Ex

ex

Combustion of hydrocarbons is exothermic because the products store less energy than the reactants

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CH4 + 2O2

CO2 + 2H2O

difference in energyexpelled as heat+light

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

• 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

• 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 and where did they come from?

• What are fossil fuels made of?• Fossil fuels are mostly hydrocarbons

• What are the harmful effects of burning fossil fuels?