chapter 9 energy and hydrocarbons. chapter outline background & energy from fuels alkanes:...

Chapter 9

Energy and Hydrocarbons

Chapter Outline

Background & Energy from FuelsAlkanes: Backbone of Organic ChemistryAlkenes and Alkynes: Reactive cousins of AlkanesCyclic HydrocarbonsPetroleumNatural GasCoalMethanol (Gasohol)

Define some terms

Energy is a common idea that ran through the first half of the class. – What is Energy?– What is Heat?– What is Temperature?– What is the difference between heat and temperature? – What are the ‘units’ of each measurement?– Exothermic vs. Endothermic

Energy

Energy is defined as ‘the capacity to do work’– What does this mean to you?

Energy: Capacity to do work or to transfer heat!

Types of Energy

Kinetic Energy – Energy of Motion

Ek = ½ mv2 m= mass (kg)

v = velocity (m/s)Ek = Joules

Potential Energy – Stored energy based on the position of one object with respect to another

Ep = m *g* h m = mass (kg)g = gravitational constant = 9.806 m/s2

h= distance above reference

Example

What is the kinetic Energy of a bowling ball moving at a velocity of 1.5 m/s? (Mass of bowling ball = 7.5 kg)

Ek = ½ mv2

Units of Energy

Heat can have the following units– Joules (J) = 1 kg*m2/s2

– Kilojoules(kJ)– calories (cal) = 4.184 Joule– Kilocalories (kcal) = 1000 calories– Dietary Calories = Calories (Cal) = 1 kcal– Erg– BTU– Foot-pounds

Energy

Calculate the amount of potential energy of a 1 kg book raised about 6 ft (~2 meters) into the air.

First Law of Thermodynamics

Energy is neither created nor destroyed. – The Energy is said to be “transferred or

transformed”!

What happened to the energy of the book?

Heat vs. Temperature

Some of the energy was transformed to sound energy and some converted to heat!

WHAT IS HEAT?– Before we consider heat … let’s look at temperature!

Temperature

Think back to global warming – vibrating molecules caused an increase in

temperature

Temperature – average kinetic energy of molecules in a substance.

What is Heat?

Heat is the total amount of energy in a substance– In other words – its the amount of thermal energy that a

system contains.

Heat Energy = (specific heat)*(amount of substance)*(Temperature)

What’s the difference between Heat and Temperature?Think of this Example – A drop of boiling water and 4 liters of boiling water. Which one has more energy?

What is a calorie?

Based on the work of James Joule (late 1800’s)– One calorie = amount of heat required to raise 1

gram of water 1 degree Celsius.

– One calorie = 4.184 Joules

Units of Energy

Heat can have the following units– Joules (J) = 1 kg*m2/s2

– Kilojoules(kJ)– calories (cal) = 4.184 Joule– Kilocalories (kcal) = 1000 calories– Dietary Calories = Calories (Cal) = 1 kcal– Erg– BTU– Foot-pounds

Some ‘exercises’

1. How many joules are in 425 Cal?2. How much energy is required to raise 1 gram of

water 1oC?3. How much energy is required to raise 1000

grams (1 kg) of water from room temperature (25oC) to boiling (100oC) ?

Exothermic vs. Endothermic

Draw energy diagrams for the following processes.– Dissolving of Urea in water– Dissolving of Ethanol in water

9.1 Energy from Fuels

Petroleum38%

Nuclear8%

Coal23%

Natural Gas24%

Renewable7%

Most of our energy comes from Fossil Fuels (Petroleum, Coal, Natural Gas)

Source of Energy used in the United States - 2000

Combustion of Natural Gas

Natural Gas is mostly Methane

Consider the complete combustion of methane ____ CH4 + ____ O2 -> ____ CO2 + ____ H2O

Methane Oxygen Carbon dioxide Water

Is Energy Produced? How much?

What determines if Energy is released or absorbed in a chemical reaction?

Bond Energies!!

BOND ENERGIESSingle BondsH C N O S F Cl Br I

H 432C 411 346N 386 305 167O 459 358 201 142S 363 272 - - 226F 565 485 283 190 284 155Cl 428 327 313 218 255 249 240Br 362 285 - 201 217 249 216 190I 295 213 - 201 - 278 208 175 149

Multiple BondsC=C 602 C=N 615 C=O 1072C=C 835 N=O 607N=N 418 O=O 494N=N 942 C=O 799

Bond Energies are given in kJ/mole