Specific heat of combustion. Fuel energy

15.10.2022 | Paintings by artists

Lesson developments (lesson notes)

UMK line A. V. Peryshkina. Physics (7-9)

Attention! The site administration is not responsible for the content methodological developments, as well as for compliance with the development of the Federal State Educational Standard.

“To warm others, a candle must burn”

M. Faraday.

Target: Study the issues of using the internal energy of fuel, heat release during fuel combustion.

Lesson objectives:

educational:

repeat and consolidate knowledge on the material covered;
introduce the concept of fuel energy, specific heat of combustion of fuel;
continue to develop skills in solving calculation problems.

developing:

develop analytical thinking;
develop skills in working with tables and drawing conclusions;
develop students’ abilities to put forward hypotheses, argue them, and correctly express their thoughts out loud;
develop observation and attention.

educational:

bring up careful attitude to the use of fuel resources;
cultivate interest in the subject by showing the connection between the material being studied and real life;
develop communication skills.

Subject results:

Students should know:

specific heat of combustion of fuel is physical quantity, showing how much heat is released during complete combustion of fuel weighing 1 kg;
When fuel burns, significant energy is released, which is used in everyday life, industry, agriculture, power plants, and automobile transport;
unit of measurement of the specific heat of combustion of fuel.

Students should be able to:

explain the process of energy release during fuel combustion;
use the table of specific heat of combustion of fuel;
compare the specific heat of combustion of fuels of various substances and the energy released during combustion various types fuel.

Students must apply:

formula for calculating the energy released during fuel combustion.

Lesson type: lesson of learning new material.

Equipment: candle, plate, glass, plant leaf, dry fuel, 2 alcohol lamps, gasoline, alcohol, 2 test tubes with water.

During the classes

1. Organizational moment.

Greeting students, checking readiness for the lesson.

It is known that the great scientist M.V. Lomonosov worked on the treatise “Reflections on the Cause of Heat and Cold” back in 1744. Thermal phenomena play a huge role in the world around us, in the life of humans, plants, animals, as well as in technology.

Let's check how well you have mastered this knowledge.

2. Motivation for educational activities.

Do you have any questions about homework? Let's check how you handled it:

two students present solutions to homework problems on the board.

1) Determine the absolute air humidity in a storage room with a volume of 10 m 3 if it contains water vapor weighing 0.12 kg.

2) The water vapor pressure in the air is 0.96 kPa, the relative humidity is 60%. What is the pressure of saturated water vapor at the same temperature?

1 student (Dima) fills out the diagram on the board;

task: label next to each arrow the name of the processes and the formula for calculating the amount of heat in each of them

In the meantime, the guys are working at the board, you and I will complete another task.

Look at the text shown on the slide and find in it the physical errors that the author made (suggest the correct answer):

1) On a bright sunny day, the guys went hiking. To make it not so hot, the guys dressed in dark suits. In the evening it became fresh, but after swimming it became warmer. The guys poured themselves hot tea into iron mugs and drank it with pleasure, without getting burned. It was very cool!!!

Answer: dark colors absorb more heat; During evaporation, body temperature decreases; The thermal conductivity of metals is greater, so it heats up more.

2) Waking up earlier than usual, Vasya immediately remembered that at eight in the morning he agreed with Tolya to go to the river to watch the ice drift. Vasya ran out into the street, Tolya was already there. “This is the weather today! – instead of greeting, he said admiringly. “What sunshine, and the temperature in the morning is -2 degrees Celsius.” “No, -4,” Vasya objected. The boys argued, then realized what was going on. “I have a thermometer in the wind, and you have it in a secluded place, so yours and shows more", Tolya guessed. And the guys ran splashing through puddles.

Answer: in the presence of wind, evaporation occurs more intensely, so the first thermometer should show a lower temperature; At temperatures below 00C, water freezes.

Well done, you found all the errors correctly.

Let's check the correctness of solving the problems (students who solved the problems comment on their solution).

Now let's check how Dima coped with his task.

Did Dima name all the phase transitions correctly? What happens if you place a wooden stick into a flame? (She'll burn)

You correctly noted that the combustion process occurs.

You probably already guessed what we will talk about today (they put forward hypotheses).

What questions do you think we will be able to answer at the end of the lesson?

understand physical meaning combustion process;
find out what determines the amount of heat released during combustion;
find out the application of this process in life, in everyday life, etc.

3. New material.

Every day we can watch natural gas burn in a stove burner. This is the process of fuel combustion.

Experience No. 1. The candle is fixed to the bottom of the plate using plasticine. Let's light a candle, then cover it with a jar. A few moments later the candle flame will go out.

A problematic situation is created, in which students come to the conclusion: the candle burns in the presence of oxygen.

Questions for the class:

What accompanies the combustion process?

Why does the candle go out? What are the conditions under which the combustion process occurs?

How is energy released?

To do this, let’s remember the structure of matter.

What does the substance consist of? (from molecules, molecules from atoms)

What types of energy does a molecule have? (kinetic and potential)

Can a molecule be divided into atoms? (Yes)

To divide molecules into atoms, it is necessary to overcome the attractive forces of atoms, which means doing work, that is, expending energy.

When atoms combine into a molecule, energy, on the contrary, is released. This combination of atoms into molecules also occurs when fuel is burned. Regular fuel contains carbon. You correctly determined that combustion is impossible without access to air. During combustion, carbon atoms combine with oxygen atoms in the air to form a molecule carbon dioxide and energy is released in the form of heat.

Now let's conduct an experiment and see the simultaneous combustion of several types of fuel: gasoline, dry fuel, alcohol and paraffin (Experiment No. 2).

What is common and how does the combustion of each type of fuel differ?

Yes, when any substance is burned, other combustion product substances are formed. For example, when wood burns, ash remains and carbon dioxide, carbon monoxide and other gases are released. .

But the main purpose of fuel is to provide heat!

Let's look at another experience.

Experience No. 3:(on two identical alcohol lamps: one is filled with gasoline, the other with alcohol, the same amount of water is heated).

Questions about experience:

What energy is used to heat water?

How to determine the amount of heat that went into heating the water?

In which case did the water boil faster?

What conclusion can be drawn from the experience?

Which fuel, alcohol or gasoline, released more heat during complete combustion? (gasoline has more heat than alcohol).

Teacher: A physical quantity showing how much heat is released during the complete combustion of fuel weighing 1 kg is called the specific heat of combustion of the fuel, denoted by the letter q. Unit of measurement J/kg.

The specific heat of combustion is determined experimentally using rather complex instruments.

The results of the experimental data are given in the textbook table (p. 128).

Let's work with this table.

Questions about the table:

What is the specific heat of combustion of gasoline? (44 MJ/kg)
What does this mean? (This means that the complete combustion of 1 kg of gasoline releases 44 MJ of energy).
Which substance has the lowest specific heat of combustion? (firewood).
Which fuel produces the most heat when burned? (hydrogen, because its specific heat of combustion is higher than the others).
How much heat is released when 2 kg of alcohol is burned? How did you determine this?
What do you need to know to calculate the amount of heat released during combustion?

They conclude that to find the amount of heat, you need to know not only the specific heat of combustion of the fuel, but also its mass.

This means that the total amount of heat Q (J) released during complete combustion of m (kg) of fuel is calculated by the formula: Q = q · m

Let's write it down in a notebook.

How to find the mass of fuel burned from this formula?

Express the specific heat of combustion from the formula. (You can call the student to the board to write down formulas)

Physical education minute

We are tired. Let's warm up a little. Straighten your back. Straighten your shoulders. I will name the fuel, and if you think it is solid, lower your head down, if it is liquid, then raise your hands up, and if it is gaseous, pull your hands forward.

Coal is solid.

Natural gas is gaseous.

Oil is liquid.

Wood is hard.

Gasoline is liquid.

Peat is hard.

Anthracite - hard.

Kerosene is liquid.

Coke gas is a gas.

Well done! The most attentive and sporty among us... Sit down.

Teacher: Guys! Let's think about the question: “Is the combustion process a friend or foe to man?”

Experience No. 4. Let's repeat the experiment with a burning candle, but now we'll put a plant leaf next to the candle.

Look what happened to the plant next to the candle flame?

That. When using fuel, one should not forget about the harm of combustion products to living organisms.

4. Consolidation.

Guys, please tell me, what is fuel for you and me? In the human body, food plays the role of fuel. Different types of food, like different types fuels contain different amounts of energy. (Show table on computer " Specific heat combustion of food products").

	Specific heat of combustion of fuel q, MJ/kg
Wheat bread
Rye bread
Potato
Beef
Chicken's meat
Butter


Fat cottage cheese
Sunflower oil
Grape

Chocolate roll
Ice cream

Kirieshki
Sweet tea

"Coca Cola"
Black currant

I suggest you unite in groups (1 and 2, 3 and 4 desks) and complete the following tasks (according to handouts). You are given 5 minutes to complete, after which we will discuss the results.

Group assignments:

Group 1: when preparing for lessons, you spend 800 kJ of energy within 2 hours. Will you restore your energy levels if you eat a 28g pack of chips and drink a 200g glass of Coca-Cola?
Group 2: to what height can a person weighing 70 kg rise if he eats a sandwich with butter (100g of wheat bread and 50g of butter).
Group 3: is it enough for you to consume 100 g of cottage cheese, 50 g of wheat bread, 50 g of beef and 100 g of potatoes, 200 g of sweet tea (1 glass) during the day? The required amount of energy for an 8th grade student is 1.2 MJ.
Group 4: at what speed should an athlete weighing 60 kg run if he eats a sandwich with butter (100g of wheat bread and 50g of butter).
Group 5: How much chocolate can a 55 kg teenager eat to replenish the energy he expended while reading a book while sitting? (In one hour)

Approximate energy consumption of a teenager weighing 55 kg per 1 hour during various types of activities

Washing dishes
Preparing for lessons
Reading to yourself
Sitting (at rest)
Physical exercise

Group 6: Will an athlete weighing 70 kg restore his energy reserve after swimming for 20 minutes if he eats 50 g of rye bread and 100 g of beef?

Approximate energy consumption of a person for 1 hour during various types of activities (per 1 kg of weight)

Groups present the solution to the problem on a piece of Whatman paper, then take turns going to the board and explaining it.

5. Reflection. Lesson summary.

Let's remember what tasks we set for ourselves at the beginning of the lesson? Have we achieved everything?

The guys in a circle speak in one sentence, choosing the beginning of a phrase from the reflective screen on the board:

today I found out...
it was interesting…
it was difficult…
I completed tasks...
I realized that...
Now I can…
I felt that...
I purchased...
I learned…
I managed …
I was able...
I will try…
I was surprised...
gave me a lesson for life...
I wanted…

1. What new did you learn in the lesson?

2. Will this knowledge be useful in life?

Giving lesson grades to the most active students.

6. D.z

Paragraph 10
Task (1 to choose from):

Level 1: how much heat does 10 kg of charcoal produce during combustion?
Level 2: complete combustion of oil released 132 kJ of energy. How much oil was burned?
Level 3: how much heat is released during complete combustion of 0.5 liters of alcohol (alcohol density 800 kg/m3)

Comparison table: types of fuel (advantages and disadvantages)

Thermal machines in thermodynamics, these are periodically operating heat engines and refrigeration machines (thermocompressors). A type of refrigeration machine is heat pump.

Devices that perform mechanical work due to the internal energy of the fuel, are called heat engines (heat engines). For the operation of a heat engine, the following components are required: 1) a heat source with a higher temperature level t1, 2) a heat source with a lower temperature level t2, 3) a working fluid. In other words: any heat engines (heat engines) consist of heater, refrigerator and working fluid .

As working fluid gas or steam are used, since they are well compressed, and depending on the type of engine, there may be fuel (gasoline, kerosene), water vapor, etc. The heater transfers a certain amount of heat (Q1) to the working fluid, and its internal energy increases due to this internal energy, mechanical work is performed (A), then the working fluid gives off a certain amount of heat to the refrigerator (Q2) and is cooled to the initial temperature. The described diagram represents the engine operating cycle and is general; in real engines, the role of a heater and a refrigerator can be performed by various devices. The environment can serve as a refrigerator.

Since in the engine part of the energy of the working fluid is transferred to the refrigerator, it is clear that not all the energy it receives from the heater is used to perform work. Respectively, efficiency engine (efficiency) is equal to the ratio of the work done (A) to the amount of heat it receives from the heater (Q1):

Internal combustion engine (ICE)

There are two types of internal combustion engines (ICE): carburetor And diesel. In a carburetor engine, the working mixture (a mixture of fuel and air) is prepared outside the engine in a special device and from it enters the engine. In a diesel engine, the fuel mixture is prepared in the engine itself.

ICE consists of cylinder , in which it moves piston ; there are in the cylinder two valves , through one of which the combustible mixture is admitted into the cylinder, and through the other, exhaust gases are discharged from the cylinder. Piston using crank mechanism connects with crankshaft , which comes into rotation at forward movement piston The cylinder is closed with a lid.

The internal combustion engine operating cycle includes four bars: intake, compression, stroke, exhaust. During intake, the piston moves down, the pressure in the cylinder decreases, and a combustible mixture (in a carburetor engine) or air (in a diesel engine) enters it through the valve. The valve is closed at this time. At the end of the intake of the combustible mixture, the valve closes.

During the second stroke, the piston moves up, the valves are closed, and the working mixture or air is compressed. At the same time, the gas temperature rises: the combustible mixture in a carburetor engine heats up to 300-350 °C, and the air in a diesel engine - up to 500-600 °C. At the end of the compression stroke, a spark jumps in the carburetor engine and the combustible mixture ignites. In a diesel engine, fuel is injected into the cylinder and the resulting mixture spontaneously ignites.

When a combustible mixture is burned, the gas expands and pushes the piston and the crankshaft connected to it, performing mechanical work. This causes the gas to cool.

When the piston reaches the lowest point, the pressure in it will decrease. When the piston moves upward, the valve opens and exhaust gas is released. At the end of this stroke the valve closes.

Steam turbine

Steam turbine It is a disk mounted on a shaft on which the blades are mounted. Steam enters the blades. Steam heated to 600 °C is directed into the nozzle and expands in it. When steam expands, its internal energy is converted into kinetic energy of the directed movement of the steam jet. A jet of steam comes from the nozzle onto the turbine blades and transfers part of its kinetic energy to them, causing the turbine to rotate. Typically, turbines have several disks, each of which transfers part of the steam energy. The rotation of the disk is transmitted to a shaft to which an electric current generator is connected.

When different fuels of the same mass are burned, different amounts of heat are released. For example, it is well known that natural gas is an energy-efficient fuel than wood. This means that to obtain the same amount of heat, the mass of firewood that needs to be burned must be significantly greater than the mass natural gas. Consequently, different types of fuel from an energy point of view are characterized by a quantity called specific heat of combustion of fuel .

Specific heat of combustion of fuel- a physical quantity showing how much heat is released during complete combustion of fuel weighing 1 kg.

The specific heat of combustion is indicated by the letter q , its unit is 1 J/kg.

The specific heat value is determined experimentally. Has the highest specific heat of combustion hydrogen , the smallest - powder .

The specific heat of combustion of oil is 4.4*10 7 J/kg. This means that with complete combustion of 1 kg of oil, the amount of heat released is 4.4 * 10 7 J. In the general case, if the mass of fuel is equal to m , then the amount of heat Q released during its complete combustion is equal to the product of the specific heat of combustion of the fuel q to its mass:

Q = qm.

Physics lesson notes in 8th grade “Thermal engines. ICE. Specific heat of combustion".

specific heat of combustion- specific heat capacity - Topics oil and gas industry Synonyms specific heat capacity EN specific heat ...

The amount of heat released during complete combustion of fuel weighing 1 kg. The specific heat of combustion of fuel is determined experimentally and is the most important characteristic of fuel. See also: Fuel Financial Dictionary Finam... Financial Dictionary

specific heat of combustion of peat by bomb- Higher heat of combustion of peat, taking into account the heat of formation and dissolution in sulfuric and nitric acids. [GOST 21123 85] Inadmissible, not recommended calorific value of peat for a bomb Topics peat General terms properties of peat EN ... ... Technical Translator's Guide

specific heat of combustion (fuel)- 3.1.19 specific heat of combustion (fuel): The total amount of energy released under regulated conditions of fuel combustion. Source …

Specific heat of combustion of peat by bomb- 122. Specific heat of combustion of peat by bomb Higher heat of combustion of peat taking into account the heat of formation and dissolution of sulfuric and nitric acids in water Source: GOST 21123 85: Peat. Terms and definitions original document... Dictionary-reference book of terms of normative and technical documentation

specific heat of combustion of fuel- 35 specific heat of combustion of fuel: The total amount of energy released under specified fuel combustion conditions. Source: GOST R 53905 2010: Energy saving. Terms and definitions original document... Dictionary-reference book of terms of normative and technical documentation

This is the amount of heat released during complete combustion of mass (for solids and liquid substances) or volumetric (for gaseous) units of a substance. Measured in joules or calories. Heat of combustion per unit mass or volume of fuel, ... ... Wikipedia

Modern encyclopedia

Heat of combustion- (heat of combustion, calorie content), the amount of heat released during complete combustion of fuel. There are specific heats of combustion, volumetric heats, etc. For example, the specific heat of combustion of coal is 28 34 MJ/kg, gasoline is about 44 MJ/kg; volumetric... ... Illustrated Encyclopedic Dictionary

Specific heat of combustion of fuel- Specific heat of combustion of a fuel: the total amount of energy released under specified combustion conditions...

(Fig. 14.1 - Calorific value
fuel capacity)

Pay attention to the calorific value (specific heat of combustion) of various types of fuel, compare the indicators. The calorific value of fuel characterizes the amount of heat released during complete combustion of fuel weighing 1 kg or volume 1 m³ (1 l). Most often, calorific value is measured in J/kg (J/m³; J/l). The higher the specific heat of combustion of the fuel, the lower its consumption. Therefore, calorific value is one of the most significant characteristics of fuel.

The specific heat of combustion of each type of fuel depends on:

From its flammable components (carbon, hydrogen, volatile combustible sulfur, etc.).
From its moisture and ash content.

Table 4 - Specific heat of combustion of various energy carriers, comparative analysis expenses.
Type of energy carrier	Calorific Value				Volumetric density of matter (ρ=m/V)	Unit price standard fuel	Coeff. useful action (efficiency) of the system heating, %	Price per 1 kWh	Implemented systems
	MJ		kWh
	(1MJ=0.278kWh)
Electricity	-		1.0 kWh		-	3.70 rub. per kWh	98%	3.78 rub.	Heating, hot water supply (DHW), air conditioning, cooking
Methane (CH4, temperature boiling point: -161.6 °C)	39.8 MJ/m³		11.1 kWh/m³		0.72 kg/m³	5.20 rub. per m³	94%	0.50 rub.
Propane (C3H8, temperature boiling point: -42.1 °C)	46,34 MJ/kg	23,63 MJ/l	12,88 kWh/kg	6,57 kWh/l	0.51 kg/l	18.00 rub. hall	94%	2.91 rub.	Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, baths, designer lighting
Butane C4H10, temperature boiling point: -0.5 °C)	47,20 MJ/kg	27,38 MJ/l	13,12 kWh/kg	7,61 kWh/l	0.58 kg/l	14.00 rub. hall	94%	1.96 rub.	Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, baths, designer lighting
Propane-butane (LPG - liquefied hydrocarbon gas)	46,8 MJ/kg	25,3 MJ/l	13,0 kWh/kg	7,0 kWh/l	0.54 kg/l	16.00 rub. hall	94%	2.42 rub.	Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, baths, designer lighting
Diesel fuel	42,7 MJ/kg		11,9 kWh/kg		0.85 kg/l	30.00 rub. per kg	92%	2.75 rub.	Heating (heating water and generating electricity is very expensive)
Firewood (birch, humidity - 12%)	15,0 MJ/kg		4,2 kWh/kg		0.47-0.72 kg/dm³	3.00 rub. per kg	90%	0.80 rub.	Heating (inconvenient to cook food, almost impossible to get hot water)
Coal	22,0 MJ/kg		6,1 kWh/kg		1200-1500 kg/m³	7.70 rub. per kg	90%	1.40 rub.	Heating
MAPP gas (a mixture of liquefied petroleum gas - 56% with methyl acetylene-propadiene - 44%)	89,6 MJ/kg		24,9 kWh/m³		0.1137 kg/dm³	-R. per m³	0%		Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, baths, designer lighting

(Fig. 14.2 - Specific heat of combustion)

According to the table “Specific Heat of Combustion of Various Energy Carriers, Comparative Analysis of Costs,” propane-butane (liquefied petroleum gas) is inferior in economic benefits and prospects for use only to natural gas (methane). However, attention should be paid to the tendency towards an inevitable increase in the cost of main gas, which is currently significantly underestimated. Analysts predict an inevitable reorganization of the industry, which will lead to a significant increase in the price of natural gas, perhaps even exceeding the cost of diesel fuel.

Thus, liquefied petroleum gas, the cost of which will remain virtually unchanged, remains extremely promising - the optimal solution for autonomous gasification systems.