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Calorific Value is an important parameter used to determine the energy content of various items mainly fuels and food items. It is commonly used to judge the fuel efficiency and the heat produced by the human body.
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Key Terms: Calorific value, combustion, Gross Calorific Value, fuel, Energy, Heat, volume
Definition of Calorific Value
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Calorific value refers to the amount of heat produced by unit volume of a substance on complete combustion. It is expressed in kilojoules/kilogram. It is also called Calorific Power. Calorific value is the heat contained in fuels or food, which is determined by complete combustion of specified quantities at constant pressure and in normal conditions.
Determination of Calorific Value with Bomb Calorimeter
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Calorific Value: Measurement and Formula
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Calorific value is the heat produced by unit volume of a substance on complete combustion. It is measured in Kilojoules/kilogram or kJ/kg.
For example: When we say that the calorific value of kerosene is 45000 kJ/kg- it means that if 1 kg of kerosene is completely combusted, it will produce 45000 kilojoules of heat energy.
Formula to Calculate Calorific Value
The formula for calculating calorific value is:
| Calorie Value = (Heat produced in Kilojoules) / (Amount of fuel consumed in kg) |
There are 2 types of Calorific value and the relation between them is:
| Gross Calorific Value = Net calorific value + Latent heat of water vapour |
Here Gross Calorific Value is the heat produced on burning 1 kg of the substance and then cooled to room temperature as the water vapour generated in the combustion process also produces heat which should be recovered.
Greater the heat recovered from the water vapour, greater is the Gross Calorific Value.
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Calorific Value of Fuels
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Calorific Value is the heat produced on complete combustion of 1 kg of fuel. Calorific Value is mainly used to determine the efficiency of the fuels. Greater the calorific value, greater is the efficiency of the fuel and better the fuel.
The amount of heat generated by different types of fuels varies, depending on the nature of the element and the proportion of the elements present in them.
When fuels are burnt, it has the capability of generating electricity in the thermal power generating plants. The best fuel to produce electricity largely depends on its calorific value.
Here is a list of fuels and their calorific values:
| Fuel | Calorific Value of the fuel |
|---|---|
| Cow Dung Cake | 6000-8000 |
| Wood | 17000-22000 |
| Coal | 25000-33000 |
| Petrol | 45000 |
| Kerosene | 45000 |
| Diesel | 45000 |
| Methane | 50000 |
| CNG | 50000 |
| LPG | 55000 |
| Biogas | 35000-40000 |
| Hydrogen | 150000 |
Calorific Value of Food
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The Calorific Value of food is the heat energy produced in the human body during metabolism. The energy present in the food items, when digested, breaks down to produce fuel for the body to carry out daily activities. It is commonly denoted in Kilocalories.
It is the amount of energy required to raise the temperature of the 1 litre of water by 1 degree.
The table below represents various food items and their calorific values:
| Food Category | Kilojoules per gram | Kilocalories per gram |
|---|---|---|
| Dietary Fibre | 8 | 2 |
| Polyhydric Alcohols | 10 | 2.4 |
| Alcohol | 29 | 7 |
| Carbohydrates | 17 | 4 |
| Protein | 17 | 4 |
| Fats | 37 | 9 |
The commonly held belief of avoiding fat while dieting is because fats have the highest calorific value as compared to other macronutrients.
Applications of Calorific Value
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- Calorific value is used in gas shippers and suppliers to bill consumers.
- The calorie intake of humans through food helps humans to remain healthy. Some regular intake of calories is essential to carry out daily activities. Lower or Higher intake of calories can lead to health issues.
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Importance of Calorific Value
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- Since fuels and foods are significant parts of our lives, it is important to keep a track of the amount of energy consumed or transported.
- Keeping awareness of the calorific value of fuels and food helps us undertake easy calculations. It also helps in determining the transportation charges. On the other hand, calorific value calculation of food will help in guiding people towards a balanced calorie or food consumption, which would ensure better health.
- Food with too little or too high calorific value can cause health problems. Thus, it should be kept in mind that the body will be able to carry out daily activities and will remain fit if calories are consumed in a specific range.
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Things to Remember
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- The units in which Calorific values are generally for fuels is kilojoules/kilogram and for food it is kilocalories/gram.
- Fuels with higher Calorific value are considered to be good fuel.
- Higher the calorific value of the fuel, higher is the efficiency.
- Proper intake of calories is required for the human body to stay healthy.
- Fat is an energy rich macronutrient.
- Calorific values are a good indicator for defining the commercial value of a material, as higher the value, higher is the efficiency of the material.
Read more : Class 11 Biology Chapter 15 Plant Growth and Development
Previous Years Questions
- A few normal seedlings of tomato were kept in...[NEET 2014]
- One set of a plant was grown at 12 hours day and 12 hours night period cycles….[NEET 2004]
- Treatment of seed at low temperature under moist ….[NEET 2006]
- Abscisic acid controls...[NEET 1990]
- Hormone connected with cell division...[NEET 1991]
- Auxin can be bioassayed by...[NEET 2015]
- Coiling of garden pea tendrils around any support….[NEET 2010]
- Cytokinins are known to….[NEET 1992]
- Dwarfness can be controlled by treating the plant...[NEET 1980]
- Flowering dependent on cold treatment is...[NEET 1992]
- Fruit and leaf drop at early stages can be….[NEET 2017]
- Gibberellins promote...[NEET 1988]
- If the apical bud has been removed observe...[NEET 2000]
- If the growing plant is decapitated….[NEET 1994]
Sample Questions
Ques. Name the unit in which calorific value is expressed? (1 Mark)
Ans. Calorific value is expressed in Kilojoules/Kilograms (kJ/kg).
Ques. What is the Gross Calorific Value and the Physiological value of Fat respectively. (1 Mark)
Ans. Gross Calorific Value: 9.45 Kcal/g
Physiological Value: 9 Kcal/g
Note: Gross Calorific Value of food is the energy released by one gram of food and the Physiological Value of food is the actual energy liberated in the body by carbohydrates, fats and proteins.
Ques. What does the Calorific Value of a fuel depend on? (2 Marks)
Ans. The Calorific value of a fuel depends on the nature of the fuel and the relative proportions of the elements present. It increases with the increase in the amounts of hydrogen and decreases with the moisture content present in the fuel.
Ques. Which fuel has the highest Calorific Value? (2 Marks)
Ans. Hydrogen. It has a Calorific value of 150000 kJ/kg.
Calorific value is nothing but the energy contained in a fuel or food, determined by measuring the heat produced by the complete combustion of a specified quantity of it. This is now usually expressed in joules per kilogram. Hence, hydrogen has the highest calorific value.
Ques. What are the 2 types of Calorific Value? (2 Marks)
Ans. The 2 types of calorific values are:
Higher Calorie Value or the Gross Calorie Value(GCV): When 1 kg of fuel is burned and cooled down to room temperature, the heat obtained is the GCV.
Lower Calorie Value or the Net Calorie Value(NCV): When 1 kg of fuel is burned, the heat obtained is the NCV. But here the product is not cooled down to room temperature and neither is the heat generated during the burning is condensed.
Ques. Compare LPG and Wood as fuels. (3 Marks)
Ans. The comparison between LPG and Wood as fuels is tabulated below:
| LPG | Wood |
|---|---|
| LPG is in liquid form and is known as Liquified Petroleum Gas. | Wood is in solid form |
| It has high calorific value and doesn’t harm the environment, hence is an Ideal fuel. | It has comparatively low calorific va;ue and creates a lot of smoke and pollution, along with deforestation, hence it is not an Ideal fuel. |
| The calorific value of LPG is 55000 kJ/kg. | The calorific value of Wood is 17000-22000 kJ/kg. |
Ques. Define Ideal fuels and give examples for the same. (3 Marks)
Ans. An Ideal Fuel is a fuel which is easily available and affordable, doesn’t harm the environment or cause pollution, has a high calorific value and has a moderate rate of combustion.
Examples of Ideal Fuels are:
LPG which has a high calorific value of 55000 kJ/kg and CNG too, which also has a high calorific value of 50000 kJ/kg. Both fuels don't harm the environment as well.
Ques. Calorific value of Carbohydrate, Protein and Fats are:
a.5.65 kcal/g, 10 kcal/g, 2.3 kcal/g
b.4.1 kcal/g, 5.65 kcal/g, 9.45 kal/g
c.3.1 kcal/g, 9 kcal/g, 6 kcal/g (4 Marks)
Answer:
Carbohydrates: They are naturally occurring sugar, fibres and starch in food. When metabolized glucose converts into pyruvate during glycolysis and even to lactate when there is absence of oxygen. For example: vegetables, pasta, rice, grain and each gram of carbohydrates contain 4kacl/g.
Protein: Protein is macromolecules and is a polymer of amino acids which are the building blocks of life. Proteins are the necessary macromolecules whose deficiency in the body can lead to some disorders. Sources of proteins are:- egg, meat, poultry products. The calorific value of proteins is the same as carbohydrates.
Fats: Fats are the slowest form of energy and lately digest. Some foods like sausages, potato contain higher calories and lower vitamins and minerals so that as compared to above two fats have high calorific value.
To calculate the calorific value any macromolecule:
The formula used will be heat/kilogram
Heat calculated in the above formula will be measured in kilojoules kilogram which is equal to total combustion in kg.
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