Greetings,
This post covers Heat of Combustion and the method by which it is commonly determined, Bomb Calorimetry. Heat of Combustion is the enthalpy change (aka, Heat of Reaction) for the complete reaction of a compound with oxygen. Heat of Combustion is an important chemical property of organic compounds because it provides useful information such as the energy content of a fuel and the diet calorie content of sugars. This post will focus on the principle source of heat energy in the human body, Glucose.
Glucose is a carbohydrate, which means that its metabolism products are carbon dioxide and water. In the early days of Organic Chemical Synthesis and Biochemistry, a carbohydrate was thought to be a "chemical mixture" of carbon dioxide and water; which is the root source of the carbohydrate name. Modern chemistry has clearly demonstrated that a carbohydrate is not simply a mixture of carbon dioxide and water, but the name stuck and is still used today.
For this post, let's assume that our calorimeter has a heat capacity of 750 cal/K. For a detailed explanation of bomb calorimetry calibration, see http://www.chem.hope.edu/~polik/Chem345-2000/bombcalorimetry.htm . Then, we can easily calculate the Heat of Combustion for our 1.000 g sample of glucose. Hc(glucose) = -{(27.50 - 22.50)K * 750 cal/K}/1.000 g = -3750 cal/g
The reference Heat of Combustion for glucose is - 3715 cal/g. (http://www.chegg.com/homework-help/questions-and-answers/heat-enthalpy-combustion-glucose-c6h12o6-2800-kj-mol-e-combustion-glucose-25-oc-hint-need--q1175777) .
That's all for now. As always, thank you for reading!
A Publication of http://ExcellenceInLearning.biz
This post covers Heat of Combustion and the method by which it is commonly determined, Bomb Calorimetry. Heat of Combustion is the enthalpy change (aka, Heat of Reaction) for the complete reaction of a compound with oxygen. Heat of Combustion is an important chemical property of organic compounds because it provides useful information such as the energy content of a fuel and the diet calorie content of sugars. This post will focus on the principle source of heat energy in the human body, Glucose.
Glucose is a carbohydrate, which means that its metabolism products are carbon dioxide and water. In the early days of Organic Chemical Synthesis and Biochemistry, a carbohydrate was thought to be a "chemical mixture" of carbon dioxide and water; which is the root source of the carbohydrate name. Modern chemistry has clearly demonstrated that a carbohydrate is not simply a mixture of carbon dioxide and water, but the name stuck and is still used today.
Bomb Calorimetry
A bomb calorimeter is a measuring device used to determine the Heat of Combustion of a compound. Heat of Combustion is commonly expressed as calories per gram or Joules per gram. A student of chemistry may recall that 4.184 Joules of heat energy are equivalent to 1 calorie. Additionally, the knowledgeable chemistry student will remember that a calorie is the amount of heat required to increase the temperature of 1 mL of water by 1 deg. Celsius. Other common expressions for Heat of Combustion are kilocalories per mole (Kcal/mol) and kilojoules per mole (KJ/mol).
A bomb calorimeter consists of 3 chambers; 1) an inner chamber where a sample is ignited ("the bomb"), 2) a "water bucket" in which the bomb is completely submerged, and 3) a water jacket surrounding the bomb and bucket chambers. Ideally, the outer jacket temperature is controlled to match the temperature of the water bucket. The effect is a very efficient containment of combustion heat energy, leading to a very accurate determination of Heat of Combustion. When the outer jacket temperature is set to match the water bucket chamber, we say that we are operating in "adiabatic mode". The following presentation demonstrates the operation of a bomb calorimeter for a sample of glucose.
A bomb calorimeter consists of 3 chambers; 1) an inner chamber where a sample is ignited ("the bomb"), 2) a "water bucket" in which the bomb is completely submerged, and 3) a water jacket surrounding the bomb and bucket chambers. Ideally, the outer jacket temperature is controlled to match the temperature of the water bucket. The effect is a very efficient containment of combustion heat energy, leading to a very accurate determination of Heat of Combustion. When the outer jacket temperature is set to match the water bucket chamber, we say that we are operating in "adiabatic mode". The following presentation demonstrates the operation of a bomb calorimeter for a sample of glucose.
For this post, let's assume that our calorimeter has a heat capacity of 750 cal/K. For a detailed explanation of bomb calorimetry calibration, see http://www.chem.hope.edu/~polik/Chem345-2000/bombcalorimetry.htm . Then, we can easily calculate the Heat of Combustion for our 1.000 g sample of glucose. Hc(glucose) = -{(27.50 - 22.50)K * 750 cal/K}/1.000 g = -3750 cal/g
The reference Heat of Combustion for glucose is - 3715 cal/g. (http://www.chegg.com/homework-help/questions-and-answers/heat-enthalpy-combustion-glucose-c6h12o6-2800-kj-mol-e-combustion-glucose-25-oc-hint-need--q1175777) .
That's all for now. As always, thank you for reading!
A Publication of http://ExcellenceInLearning.biz