u3s4 L1 & L2What fuels you?

Thermodynamics STSE issues

Textbook Readingspage 692 -702 Textbook Practice Itemspage 702: item1 page 705: item 22page 705: item 23

Upon completion of this lesson, you should be able to: • identify and describe sources of energy including present sources and

possible new sources • compare physical, chemical, and nuclear changes in terms of the species

and the magnitude of energy involved • define, calculate and compare fuel values • propose and analyze solutions to energy problems using the concept of

fuel value • analyze examples where technologies were developed based on

thermochemistry using the idea of choice of fuel in a device • identify perspectives that influence a decision involving fuels used in

devices and choices made in the Calorie content and servings of the food we eat

• analyze scientific and technological activities that take place when making choices for maintaining a healthy lifestyle

• analyze the risks and benefits to society and the environment in relation to fossil fuel use and healthy lifestyle choices

• analyze the knowledge acquired in the study of thermochemistry to identify areas of further study, specifically chemical engineering and nutrition

Sources of energy:1. Fossil fuels

• carbonized organic matter• Non-renewable• Greenhouse gas emissions

2. Solar • solar collectors / panels

3. Hydrogen • electrolysis of water. Burned or used in fuel

cells to create electricity

3. Ethanol • fermentation of grains

4. Nuclear• Nuclear reactors boil water to create steam which then turns

turbines.• A chunk of uranium the size of your fist releases a quantity of

heat equal to that of the combustion of three tonnes of coal. • clean energy - comes without the production of oxides of

carbon, nitrogen and sulfur.• the potential of nuclear fuel is too valuable and too clean to

be ignored.

5. Mechanical • wind, tidal, hydro,

Photsynthesis

Fermentation

Comparisons of molar heatsNuclear > chemical > phase changes

• Physical changes involve enthalpies in the order of 10's of kiloJoules. (∆Hvap=40.7 kJ/mol)

• Chemical changes involve enthalpies in the order of 100's or 1000's of kiloJoules. (∆Hcombustion, coal = -3900.0 kJ/mol)

• Nuclear changes (fusion / fission of nuclei) involve enthalpies in the order of billions (109) of kiloJoules. (∆Hfusion, U = -2.1 x 10+10 kJ/mol)

• 21 billion kilojoules per mole!!!!

Fuel Value• A fuel is any substance from which energy can be

derived • Fuel value is defined as the heat evolved per

gram of fuel burned.

– Fuel values allow comparisons based on mass - a unit of measurement that most people are familiar with and one that is easily measured.

mFVq

Calculate the fuel value of this juice pack.

Fuel / Chemical FormulaMolar Enthalpy of

Combustion (kJ/mol)

Fuel Value (kJ/g)

hydrogen, H2 -285.8 141.5

ethanol, C2H5OH -1366.7 29.66

methane, CH4 -890.5 55.48

propane, C3H8 -2020.0 50.33

butane, C4H10 -2658.7 51.65

octane, C8H18 -5450.2 47.70

2,2,4-trimethylpentane, C8H18 -5455.9 47.75

Based on this data, why do they use liquid H2 as a fuel on rockets?

Per gram of mass, hydrogen releases about three times as much heat than the hydrocarbons. A smaller fuel load means a larger payload.

Fueling your body:• Cellular respiration is a process that occurs in the cells of your

body.

– It is a complex series of catalysed chemical reactions that convert the potential energy of glucose to potential energy in molecules known as ATP - adenosine triphosphate.

– ATP provides the energy that drives other reactions like protein synthesis in your body. The overall equation for cellular respiration is:

What do you notice about this equation?

Food Calorimetry• Energy content of food can be determined by bomb calorimetry. • The procedure is similar to that for any bomb calorimetry trial, except that

foods are typically dehydrated so that the energy needed to heat and evaporate the water content does not affect the results.

– Example:• A 2.50 g sample of Brand X granola bar is placed in a bomb calorimeter with

a heat capacity of 13.17 kJ/°C. Upon complete combustion of the sample, the temperature of the calorimeter increases by 3.86°C. Calculate the number of Calories in a 23.0 g serving of a Brand X granola bar.

4-9-4 method• A more useful method of determining the energy content of foods

is to determine the masses of carbohydrate, fat and protein in a sample and multiply these values by their corresponding fuel values 4.2 Cal/g, 9.1 Cal/g and 4.2 Cal/g. This method is known as the 4-9-4 method.

(1 Food Calorie = 4.184 kJ)

• It is a convenient way to to keep track of your Calorie intake, especially if you have to follow a strict diet.

The Nutrition Label on a 270g bag of Krusty® potato chips states that a serving is 28g (approximately 20 chips). The Calorie content in one serving is 644 kJ ( 154 Cal ).

(a) How many servings are in a single bag of Krusty® potato chips?

(b) How much energy is consumed if the full bag is eaten?

(c) How many calories are consumed if the full bag is eaten?

(d) For the following activities, calculate the number of hours it would take doing the activity to "burn off" the full bag of Krusty® chips: (i) running at 10km/h (3140 kJ/h)

(ii) rowing (3500 kJ/h)

(iii) Walking at 6 km/h (1675 kJ/h)