Energy Content of Food

As I read the"nutritional information" panel on my box of cereal this morning I wondered how you would measure the "energy content" of food.
At AUS-e-TUTE we've come up with a straight-forward experiment that you could do in the school laboratory (or at home if you really wanted too!). We even provided some sample results and calculations so that you can measure the energy content of your favourite foods.

If you are an AUS-e-TUTE Member, you will also find additional resources such as a game, test and drill with worked solutions to help you prepare for your exams.

If you are not an AUS-e-TUTE member, you can access a "free-to-view" tutorial for evaluation purposes at http://www.ausetute.com.au/heatfood.html

What makes a good fuel?

There are lots of fuels to choose from.
Some are non-renewable fossil fuels such as oil, kerosene, petrol or gasoline, diesel or petrodiesel, coal, natural gas, coal seam gas (CGS).
Some are renewable biofuels like biodiesel, bioethanol, biogas.
How can chemistry help us decide which fuel to use?
I'm glad you asked!
AUS-e-TUTE has just added new resources (tutorial, game, test, exam, drill) to help you understand how a fuel is chosen for a purpose.
AUS-e-TUTE Members should log-in to use the new resources.
If you are not an AUS-e-TUTE, you can now access a "free-to-view" Comparing Fuels tutorial at http://www.ausetute.com.au/fuelenergy.html

Biodiesel

What's the difference between diesel and biodiesel?
I'm glad you asked!
AUS-e-TUTE has just added new resources (tutorial, game, test, exam) to help you learn how to synthesize and characterize biodiesel, as well as to distinguish between diesel and biodiesel.
AUS-e-TUTE Members should log-in to access these new resources: http://www.ausetute.com.au

If you are not an AUS-e-TUTE Member, there is a "free-to-view" biodiesel temporarily available at http://www.ausetute.com.au/biodiesel.html for evaluation purposes.

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Go to http://www.ausetute.com.au/membership.html

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Go to http://www.ausetute.com.au/register.html

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Go to http://www.ausetute.com.au

Joules, Kilojoules and Calories

What units are used to measure energy?
Well, that depends on who you are and what you are doing!
If you are a chemistry student, your preferred unit should be joules, but it is likely that you will have to convert between joules and kilojoules quite often.
You might also come across calories and kilocalories as a unit of measurement of energy, and you will then need to convert between these units, and between these and joules and kilojoules.

AUS-e-TUTE has set of resources to help you learn how do these conversions, and to practice your conversion skills.

There is currently a free-to-view tutorial available for evaluation purposes at:

http://www.ausetute.com.au/energyconv.html

Heat of Neutralisation

AUS-e-TUTE has added a new tutorial, game, test and exam on the topic of heat of neutralisation.

Visit http://www.ausetute.com.au and log-in.
The new resources are in the Thermochemistry section.

AUS-e-NEWS June 2013

Have you ever noticed that the price of E10 fuel, also known as gasohol, is less than the price of petrol (gasoline) ?

Just today, when I went to put fuel into my car, the price for standard unleaded petrol (ULP) was 130.6 cents per litre while the price of E10 fuel was 128.4 cents per litre.

Will using E10 instead of ULP save me money?

Read the June 2013 edition of AUS-e-NEWS to find out!

Haven't received your newsletter?

Email AUS-e-TUTE: 

Skutterudites and Thermoelectric Generators

More than 60 percent of the energy produced by cars, machines, and industry around the world is lost as waste heat. If we could use this wasted energy we could improve the efficiency with which we use fuels, and benefit the environment.

Thermoelectric generators are devices which convert heat energy directly into electrical energy. Semi-conducting bismuth telluride, Bi₂Te₃, can be used to convert heat into electrical energy, but it is only about 5% efficient, too low to be useful in practical thermoelectric generators.
A number of scientists have been working with skutterudites to see if they can be used to increase the efficiency of thermoelectric generators.
Skutterudites have the general formula MX₃ in which M can be cobalt, rhodium or iridium, and X can be phosphorus, arsenic or antimony. The most promising of these compounds have been the CoSb₃. These compounds have 32 atoms in the unit cell and can be represented with the Co atoms occupying the corners of cubes.
The thermal conductivity of CoSb3 is too high for them to be used effectively.

So scientists have tried adding fillers to the structure to reduce the thermal conductivity. Rare earth elements and alkaline earth metals have been used as fillers.

Until recently these compounds have taken many days to make and have been expensive to produce. Oregan State University scientists have found a way to use microwaves to turn powdered metals into skutterudites in a few minutes and at a much lower cost. The first compound they produced using this technique was an indium cobalt antimonite compound in which indium is the filler.

Reference
Krishnendu Biswas, Sean Muir, M. A. Subramanian. Rapid Microwave Synthesis of Indium Filled Skutterudites: An energy efficient route to high performance thermoelectric materials. Materials Research Bulletin, 2011; DOI: 10.1016/j.materresbull.2011.08.058

Further Reading
Periodic Table
Writing Ionic Formula
Naming Ionic Compounds

Suggested Study Questions

1. Complete the following sentences:
   • A thermoelectric generator converts heat energy into ? energy.
   • A battery converts ? energy into electrical energy.
   • In a torch, the ? energy in the battery is converted into ? energy when the torch is turned on.
     
   • The ? energy in petrol (gasoline) is converted into ? energy when the fuel is combusted.
   • The ? energy released during combustion of a fuel can be converted into ? energy to move a car forward.
2. Skutterudites have the general formula MX₃. Write the formula of the skutterudite formed in each of the following situations:
   • M = cobalt and X = antimony
   • M = rhodium and X = phosphorus
   • M = iridium and X = arsenic
3. Give the name for each of the compounds formed in question 2.
4. For each of the following pairs of atoms, determine which is the most electronegative:
   • cobalt and antimony
   • rhodium and phosphorus
   • iridium and arsenic
5. Locate the elements cobalt, rhodium and iridium in the Periodic Table. In what ways do you expect these elements to be similar? Explain your answer.
6. Locate the elements phosphorus, arsenic and antimony in the Periodic Table. In what ways do you expect these elements to be similar? Explain your answer.
7. Give the names and chemical symbols of four examples of rare earth elements.
8. Give the names and chemical symbols of four examples of alkaline earth metals.
9. Write a possible formula for the skutterudite indium cobalt antimonite.
10. One structure has been represented as In_xCe_yCo₄Sb₁₂. Explain why this is an example of a skutterudite.
    
    
    
    

Making Methanol

Methanol as an energy source can be used as a fuel in the same way as petrol (gasoline), or it can be used in fuel cells. About 90% of the worldwide production of methanol is derived from methane, the main component of natural gas. Current methods for producing this methanol involve converting methane into syngas, a mixture of carbon monoxide and hydrogen, and then converting this syngas into methanol. Eliminating the syngas stage would dramatically reduce the cost of producing methanol.
But methane is not very reactive, and combines readily with oxygen only at high temperatures. A catalyst helps, but commonly used catalysts themselves work only at 300^oC or higher. At these temperatures, most of the methanol produced is oxidized to carbon dioxide and water. Indeed, methanol yields from such reactions can be as low as 2%.

A lower temperature catalyst such as platinum dissolved in concentrated sulfuric acid at 200^oC, has achieved a methanol yield of more than 70% in the laboratory, but platinum is an expensive metal.

Methane can also be converted to methanol in the laboratory using a halogen such as bromine. Using a suitable catalyst at 250^oC methane reacts with bromine to form bromomethane (methylbromide) and hydrogen bromide. Bromomethane (methyl bromide) then reacts with water to form methanol. The bromine from the hydrogen bromide can be recovered by reaction with air, and reused.

Methanol can be made by combining carbon dioxide and hydrogen. Such a process requires considerable energy just to harvest the hydrogen from water, for example. The carbon dioxide could be captured from flue gases, and even directly from the atmosphere.

Further Reading
Nomenclature
Alcohols
Balancing Chemical Equations
Combustion of Hydrocarbons
Halogenation of Hydrocarbons
Fuel Cells and Batteries
Temperature Conversions
Ideal Gas law
Yield

Study Questions

1. Write the chemical formula for each of the following:
   
   • methanol
   • methane
   • carbon monoxide
   • hydrogen gas
   • oxygen gas
   • carbon dioxide
   • water
   • bromine liquid
   • bromomethane (methylbromide)
   • hydrogen bromide
2. Write balanced chemical equations for each of these reactions:
   
   • carbon monoxide + hydrogen gas → methanol
   • carbon dioxide + hydrogen gas → methanol
     
   • methane + oxygen gas → carbon dioxide gas + water
   • methane + oxygen gas → methanol
   • methane + bromine liquid → bromomethane + hydrogen bromide
   • bromomethane + water → methanol + hydrogen bromide
     
   • water → hydrogen gas + oxygen gas
3. Convert the following temperatures in ^oC to Kelvin
   • 200^oC
   • 250^oC
   • 300^oC
   
   
4. For the reaction between methane and oxygen to produce methanol, calculate the theoretical yield of methanol that could be produced from 100kg of methane.
5. Using the platinum-based sulfuric acid catalyst at 200^oC, yields of 70% have been achieved for the above reaction.
   • What mass of methanol is actually produced during this reaction if you start with 100kg of methane?
   • Convert this mass to moles.
   • Calculate the volume of methanol gas produced.
     
6. At 300^oC the yield of methanol produced from the reaction between methane and oxygen is 2%. Assume the reaction starts with 100L of methane gas
   • Calculate the moles of methane gas in the reaction mixture
   • Calculate the theoretical yield of methanol that could be produced
   • Calculate the actual yield of methanol
7. Why do you think it is important for Chemists to continue to search for inexpensive catalysts for the methane to methanol reaction?