Petroleum As An Energy Source Unit 3B Petroleum As An Energy Source

What are fossil fuels? Fossil fuels are petroleum, natural gas, and coal

How are fossil fuels formed? The process begins with the Sun! The energy released by burning fossil fuels was originally captured from sunlight by prehistoric green plants.

How are fossil fuels formed? Fossil fuels originated from living matter in ancient seas some 500 million years ago. These species died and became covered with sediment. Pressure, heat, and microbes converted the matter into petroleum. The process is far too slow to consider petroleum a renewable resource.

What is Energy? Energy is the capacity to do work or supply heat. There are two main types of energy: Potential Energy: energy of position or stored energy Ex: winding up a toy car Kinetic Energy: energy of motion Ex: releasing the toy car and it moves

What kind of energy is found in fossil fuels? Chemical Energy: potential energy stored within bonds in chemical compounds Thermal Energy: (heat) – energy transferred between two objects of differing temperature In the reaction above, the chemical energy in methane gas, CH4, is converted into thermal energy when it is burned.

Other forms of energy Electrical – moving electrons Light energy – moving photons Mechanical – moving parts or objects Sound – moving energy waves we can hear

How is the chemical energy from fossil fuels converted to energy we use at home?

Energy Law of conservation of energy - in ordinary reactions energy is not created or destroyed but converted from one form to another. When energy changes forms, there is usually energy “lost” as heat.

Energy In Reactions The “universe” is composed of: System - what you are looking at AND Surroundings - everything else In chemistry, we look at everything from the systems point of view!

Endothermic Reactions Endothermic - energy is required system absorbs heat from the surroundings(+). Melting ice Boiling water Baking a potato Sweat evaporating Breaking chemical bonds!!!

Exothermic Reactions Exothermic - energy is released system loses heat to surroundings(-). Freezing water Condensing steam Combustion Warm object in a cool room (like you) Making chemical bonds!!!

Because more energy was released in making the products than was needed to break apart the reactants, the reaction is exothermic (energy is released).

Dimensional Analysis Method

Which is bigger? Answer = 5 120 Pennies 5 Quarters 21 Nickels The units are more important than the numbers!

A physical quantity must include: Number + Unit

What is Dimensional Analysis? Dimension – means Unit Analysis – means Problem Solving Math using units! Use the units to find the solution to a problem!

Conversion Factors You will use equalities to make a “conversion factor” Conversion Factor: A ratio of two equivalent values. All conversion factors are equal to 1. 60 seconds = 1 minute can be written: Both equal 1

Math Review Having the same unit on top and bottom will cancel it out! For Example: What would cancel out? What would the final unit be? 15.0 Miles 1 Gallon 10,000 Miles 1 Year Miles gal/year

Math Review To solve for the answer, multiply the top numbers together. Multiply the bottom numbers together. Then, divide the numbers. For example: To Solve: (1 x 10,000) (10,000) (15.0 x 1) (15.0) 15.0 Miles 1 Gallon 10,000 Miles 1 Year = 667 gal/year =

Practice Given the following conversion factors, determine how much gas would be used in one week in gallons/week. 225 miles 1 week 23.0 miles 1 gal 225 miles 1 week 23.0 miles 1 gal = 9.7 gal/week

Energy Conversion Efficiency 3B.5 Page 245

Energy Efficiency Petroleum is expensive and nonrenewable, therefore ways to conserve petroleum are needed. Devices that convert chemical energy to mechanical energy are less than 50% efficient. Useful energy is always “lost” in other forms, usually thermal energy (heat). How can we calculate how much fuel is used or wasted?

Let’s do a sample problem… Assume that your family drives 11700 miles each year and that the car can travel 23.0 miles on one gallon of gasoline. How many gallons of gasoline does the car use in one year? If gasoline costs $3.20 per gallon, how much money does the family spend in one year?

a. Write out four possible conversion factors Sort out the given information: You were told 2 things 23 miles per gallon and 11700 miles per year. and If needed, they may be inverted (just flipped around): and

b. How many gallons of gasoline does the car use in one year? We need to find gallons/year : Which do we use? We need gallons on top and year on the bottom! = So the answer is:

c. If gasoline costs $3.20 per gallon, how much money does the family spend in one year? We need to find money, but we have a new piece of information – gas is $3.20 per gallon: =

End Day 1

Efficiency Assume the automobile is only uses 25.0% of the energy released by burning gasoline. How many gallons of gasoline are wasted each year due to energy conversion inefficiency? How much does this wasted gasoline cost at $3.20 a gallon?

i. So if 25.0% is actually used, how percent is wasted? a. How many gallons of gasoline are wasted each year due to energy conversion inefficiency? i. So if 25.0% is actually used, how percent is wasted? 100% - 25% = 75% Remember we found that we used 509 gallons of gas per year and 75% of that was wasted. How do you find 75% of 509 gallons?

b. How much does this wasted gasoline cost at $3.20 a gallon? Again, since we are wasting 75.0% of it, we will be wasting 75.0% of our money! We can calculate the amount of money wasted using the amount of gallons wasted. =

Increasing Efficiency? Suppose that continued research leads to a car that travels 65.0 miles on one gallon of gasoline. In one year, how much gasoline would be saved compared to the first car? How much money would be saved assuming a gasoline price of $3.20 per gallon?

a. In one year, how much gasoline would be saved compared to the first car? Step 1: Like before, we begin by finding gallons/year (we travel 11700 miles per year and get 65.0 miles per gallon): = Step 2: Now, to compare that to the original engine which used 509 gallons per year: _ =

b. How much money would be saved assuming a gasoline price of $3 b. How much money would be saved assuming a gasoline price of $3.20 per gallon? We need to figure out how much we saved. Since we know how much gas we saved (329 gal/yr), we can calculate the amount of money we saved if gas costs $3.20/gal: =

Stop

3B.6 Energy & Combustion Units of Energy: calorie (cal) - heat needed to raise 1 g of water 1 C. Calorie (Cal) - food Calorie - 1000 cal Joule (J) - SI unit of energy 1Cal = 1kcal = 1000 cal = 4186 J = 4.186 kJ

Energy = mass x specific heat x change in temperature 3B.6 Energy & Combustion How do we measure the amount of energy we get when burning a hydrocarbon (or eating food)? When you burn a substance, because it is exothermic it will release energy. Energy = mass x specific heat x change in temperature E = m x C x T How do we capture and measure this energy? One method is called calorimetry!

3B.6 Combustion In a calorimeter, you use the energy to heat up water. Because it takes a specific amount of energy to heat up 1 gram of water by 1ºC, you can use this device to measure the amount of energy released. This is called the specific heat and has a value of 4.2 J/gºC for water.

3B.6 Combustion Lab In the lab, our calorimeter is a pop can containing a measured amount of water.

3B.6 Combustion Lab To minimize error do to heat loss or gain, you start with cold water and the heat water to the same temperature above room temperature that the cold water was below room temperature Room temp = 22ºC Cold water = 14ºC Heat to temp = 30ºC

3B.6 Combustion Lab If your burning candle heated 98 mL of water from 11ºC to 34ºC, how much energy did the burning candle release? E = m x C x T Mass water = Specific heat of water = Temp change = 98 g 4.2 J/gºC 34ºC – 11ºC = 23ºC = 9467 J

3B.7 Using Heats of Combustion 2C8H18 + 25O2  16CO2 + 18H2O + 10900kJ All reactions involve energy. Endothermic - energy is a reactant (left) Exothermic - energy is a product (right) Thermochemical equation - chemical equation with energy included.

3B.7 Using Heats of Combustion Heat of combustion: the quantity of thermal energy given off when a certain amount of a substance burns (kJ/g) Molar heat of combustion: the quantity of thermal energy released when one mole of a substance is burned (kJ/mol) 2C8H18 + 25O2  16CO2 + 18H2O + 10900kJ In the above reaction, for every 2moles of octane burned, 10900 kJ of energy are released. Therefore, the molar heat of combustion is 10900kJ/2mol = 5450 kJ/mol.

3B.7 Using Heats of Combustion Write the thermochemical equation for the combustion of butane. (Use p.250) What is butane? C4H10 When you burn something what is your other reactant? O2 What are your products when you burn a hydrocarbon? (Hint: p.251) CO2 + H2O What is the molar heat of combustion of butane? 2859 kJ/mol

3B.7 Using Heats of Combustion Step 1: Write the reaction. Step 2: Balance the reaction. Step 3: Calculate the energy released in the reaction. (use pg. 250 Table 3.6) If there is one mole of the hydrocarbon, the molar heat of combustion = energy released. If there is two moles of the hydrocarbon, multiply the molar heat of combustion x 2 moles. 2859 kJ/mole x 2 moles = 5718 kJ C4H10 + O2  CO2 + H2O 2C4H10 + 13O2  8CO2 + 10H2O

3B.7 Using Heats of Combustion Step 4: Add the energy released to the balance equation. 2C4H10 + 13O2  8CO2 + 10H2O + 5718 kJ

3B.9 Altering Fuels The gasoline fraction of crude oil (C5-C12) is only 18% of a barrel of oil. With the invention of the light bulb, we no longer needed the Kerosene fraction (C12-C15). What could we do with all of these extra big hydrocarbon molecules? Break, or crack, them into smaller gasoline molecules!

3B.9 Altering Fuels Cracking – process in which larger hydrocarbon molecules from petroleum are converted into smaller molecules using thermal energy and a catalyst C16H34 → C8H18 + C8H16

Catalyst used for craking 3B.9 Catalyst More than a third of all crude oil undergoes cracking The temperature has to be high enough for cracking to occur and a catalyst has to be present to speed up the reaction Catalyst – increases the speed of a chemical reaction but is not used up Aluminosilicate Catalyst used for craking

3B.9 “Pinging” and “Knocking” Gasoline is composed of mainly straight-chain alkanes, like hexane and heptane and octane. Straight chains can combust too rapidly. This causes “pinging” or “knocking” causing the piston to bang against the crankshaft, which is bad for the engine. To reduce this, they try to use a lot of branched-chain alkanes.

3B.9 Octane Rating Octane Number – Rating indicating the combustion quality of gasoline compared to the combustion quality of isooctane Isooctane is considered 100 The higher the octane number, the better the fuel Also, the higher the octane, the less “knocking” ← Isooctane

3B.9 Unleaded Why do they call gas unleaded? Gas is unleaded because prior to the 1970’s, tetraethyl lead was added to boost octane ratings. However, lead is dangerous for the environment and is no longer used.

3B.9 Oxygenated Fuels To replace lead, oxygenated fuels were developed Oxygenated Fuels – fuel with oxygen-containing additives that increase octane rating and reduce harmful emissions Although they don’t release as much energy as normal gasoline, they are more environmentally friendly to burn (but still have other issues)

3B.9 Oxygenated Fuels Sometimes blending alcohols into gasoline can conserve petroleum Gasohol – A mixture of ethanol and gasoline to conserve petroleum

3B.9 Oxygenated Fuels A major breakthrough in the late 1970’s was an oxygenated fuel additive, MTBE. MTBE had an octane rating of 116! However, there were also problems with MTBE! It’s underground storage containers began to contaminate groundwater. No longer used today.

3B.9 Octane Boosting! Another method to boost octane is to alter the structure of the hydrocarbons This is done by branching the chains, since branched alkanes combust better This is a process known as isomerization.