CHEM101: Food as Energy - Fuel For Life Chemistry Assessment Help

Task: Chemistry Assignment

Scenerio: FOOD AS ENERGY – FUEL FOR LIFE Not only do we use energy for transportation, heating, lights, and countless devices but we also need it to power our bodies. The food we eat provides energy for metabolism and physical activity. Aerobic respiration involves oxidation of the nutrient molecule to produce carbon dioxide and water. It is the same overall reaction as combustion, but proceeds by a very different pathway. The chemical energy released is harnessed to produce adenosine triphosphate (ATP), commonly described as the body’s energy “currency”. One molecule of palmitic acid for example makes about 130 molecules of ATP. Recently, controversy has erupted over whether fat or sugar is the worst culprit in the obesity epidemic. It is a complex story, but one property of nutrients that can be well determined is their energy content. In the first part of this scenario, your task is to assess which has a higher energy content, sugar or fat. These generic classes of food will be represented by sucrose (table sugar) and palmitic acid, the most abundant saturated fatty acid in food. You will use concepts of physical chemistry to examine aspects of the energy content of food, how much oxygen is required for respiration, how that oxygen is transported, and the chemical kinetic factors that determine how readily reactions occur. Q1. What functional groups are present in each molecule? Q2. Write balanced chemical equations for the aerobic respiration reaction of sucrose, showing how it reacts with oxygen to produce energy? Energy It would be very difficult to directly measure the energy released in a respiration reaction that proceeds via a complex biochemical pathway. However, thermodynamic enthalpy data is available for an equivalent overall reaction that proceeds via combustion instead. Happily, the net enthalpy change from reactants to products is the same regardless of how the reaction occurs (this is a central postulate of thermodynamics called “Hess’s Law). Q3. The molar enthalpy of combustion of sucrose, ?r Ho = is -5645 kJ mol-1. What term (one word) is used to describe a chemical reaction with a negative change in enthalpy? Q4. Calculate the molecular weights of both sucrose and palmitic acid, by summing the contributions from C, H and O atoms and enter your data in the table below. (Useful data: relative atomic masses C 12.01, H 1.01, O 16.00). Q5. Calculate the number of moles in 1.00 g of sucrose and of palmitic acid. Enter your answers in the table below. (Hint: n = m/MW). Q6. Calculate the energy released by respiration of 1.00 g of sucrose and of palmitic acid. Enter your answers in the table below. (hint: use the number of mol from the previous Q, along with the molar enthalpy of combustion) Q7. Based on the energy released in respiration per gram, which is the more potent fuel source, sugar or fat? Is this consistent with the notion that each new CO bond made via oxidation releases energy? Gases Respiration requires oxygen, but how much do we need in a day, or each minute? This is more than just a matter of curiosity for environments where air is in limited supply (e.g. in a submarine or space vessel, scuba diving, climbing in the Himalayas or trapped in an air pocket). You can get a rough estimate of this as follows by considering the oxygen required to produce the recommended daily energy quota for an adult of 8700 kJ (as seen on food labels). Q8. (a) According to the stoichiometry (molar ratios) of the balanced reaction, how many oxygen molecules are required for each sucrose molecule in respiration? Enter your answer in the table. (b) How many mole of O2 are required to generate 8700 kJ of energy from sucrose? (The appendix provides examples of this type of calculation.) (c) Use the ideal gas equation to calculate the corresponding volume of oxygen gas at standard atmospheric temperature and pressure (SATP) of 25 oC and 100 kPa (1 bar)? Enter your answer in the table. (d) State at least two limitations/assumptions in this method of estimation. Equilibrium How is O2 transported form the lungs to the body’s tissues? By bonding to the iron atoms of Haemoglobin in red blood cells, changing their colour from blue to red. Haemoglobin is a tetrameric molecule that can sequentially bind four oxygen molecules, but the equilibrium may expressed in simplified form for the first added molecule by this reaction:1 Q9. (a) What is meant by the double arrows (?) in this reaction? (b) What happens to the ratio of oxygenated HbO2(aq) to deoxygenated Hb(aq), i.e. [Hb (aq)] /[HbO (aq)] 2 , when there is a high pressure of oxygen, PO2(g), in the lungs? Q10. The magnitude of K is critical for O2 to be pass first from lungs into red blood cells and then subsequently into the tissues. (a) If K was very small, would the equilibrium favour reactants or products in the above reaction? How would that affect the proportion of oxygenated HbO2(aq) to deoxygenated Hb(aq) in blood leaving the lungs? (b) Now consider the situation in the tissues of the body that rely on diffusion of oxygen from the bloodstream. If K was very large, how would that affect the amount of oxygen passing from blood into the tissues? Q11. The equilibrium constant, K, for binding of haemoglobin for carbon monoxide, CO, is about 200- 300 times greater than for O2. Explain using chemical equilibrium principles why this makes breathing CO hazardous. Kinetics.

• Broadly speaking, the factors that influence chemical reaction rates may be summarised as follows.
• Chemical nature of reactants (Is the chemical reaction thermodynamically “downhill” so that it can occur spontaneously at all?)
• Reactant Concentration (or pressure for a gas)
• Physical state of reactants (e.g. phase, or surface area of solids)
• Presence of catalyst
• Temperature

Q12. For each of the following observations, identify which one these five factors is most important, and briefly explain how/why that is the case. (a) The ability to sustain aerobic exercise is limited by the amount of haemoglobin in the blood. (b) Non-starch polysaccharides are large complex carbohydrates, and an important source of dietary fibre. Their chemical energy content is similar to other carbohydrates like sucrose. Why is it that some bacteria can process these molecules but they do not undergo respiration via by human digestion? (c) Potato is made edible by cooking it. (d) Digestion is enhanced by chewing our food.

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