"Comprehensive Calculation of Heat" Utilization of Internal Energy PPT

Description

"Comprehensive Calculation of Heat" Utilization of Internal Energy PPT

【Topic Overview】

Heat calculation includes calculations related to specific heat capacity and calculations related to calorific value. In practice, the two are often combined, or combined with efficiency and environmental effects.

Follow these steps when solving the problem:

(1) Know clearly what kind of fuel is burning, that is, know its calorific value, quality and whether it is completely burned;

(2) Clarify whether the heat released by fuel combustion is fully utilized, and the changes in the specific heat capacity, mass and temperature of the heat-absorbing object;

(3) Clarify the required physical quantity and calculate it according to the corresponding formula. The applied formulas are Q=cmΔt, Q=mq, η=Q_"useful"/Q_"total" ×100% and their variations.

Type 1 Calculation of heat

1. (Anhui High School Entrance Examination) Crop straw can be recycled and processed into straw coal. Complete combustion of 0.5 kg of straw coal can release 1.05×107 J of heat; if this heat is completely absorbed by water with a mass of 100 kg and an initial temperature of 20°C, the water temperature can be raised to 45°C. We know that q straw coal = 2.1×107 J/kg, c water = 4.2×103 J/(kg·℃)].

2. (Jining High School Entrance Examination) Place a bottle containing cold milk in hot water (as shown in Figure A), and change the internal energy of the milk through heat transfer. Figure B shows the temperature changes of 250 g of milk and hot water over time. image, then the heat absorbed by the milk during the heating process is 1.25×104 J[c milk=2.5×103 J/(kg·℃)].

3. Figure 1 is the experimental device for "exploring the temperature change characteristics of water when it boils". 200 g of water was added to the beaker and the initial temperature was measured to be 18°C. After heating with an alcohol lamp for a period of time, the thermometer displays as shown in Figure 2. At this time, the temperature of the water is 68℃. It is known that c water = 4.2×103 J/(kg·℃), then the heat absorbed by the water is 4.2 ×104 J, these calories are equivalent to the heat released by 1.4 g of alcohol with a complete combustion calorific value of 3.0×107 J/kg.

4. A student poured a cup of cold water with a mass of 200 g and a temperature of 5°C into a cup of hot water with a mass of 100 g and a temperature of 65°C. After thermal equilibrium, the temperature of the water is 25°C (excluding heat loss).

5. When water and alcohol of equal mass release equal amounts of heat, the temperatures they drop are Δt water and Δt alcohol respectively. According to the specific heat capacity data in the table below, Δt water:Δt alcohol is (A)

The specific heat capacity of some substances c/[J/(kg·℃)]

Water 4.2×103 Alcohol 2.4×103

Ice 2.1×103 Sand and gravel 0.92×103

Kerosene 2.1×103 Mercury 0.14×103

Aluminum 0.88×103 Copper 0.39×103

A.4∶7 B.7∶4 C.1∶2 D.2∶1

6. Two identical beakers are filled with equal masses of water and kerosene respectively. Use two identical electric heaters to heat the water and kerosene for the same time respectively. It is known that c kerosene = 2.1×103 J/( kg· ℃), cwater=4.2×103 J/(kg·℃). Assume that all the heat released by the electric heater is absorbed by water and kerosene, and the temperature of kerosene increases by 40°C, then the temperature of water increases by (B)

A.10 ℃ B.20 ℃

C.40 ℃ D.80 ℃

Type 2: Calculations related to efficiency

7. Use a gas stove to heat 1 kg of water with an initial temperature of 20 ℃ to 70 ℃, consuming 10 g of gas. It is known that c water = 4.2×103 J/(kg·℃), the calorific value of gas q=4.2×107 J/kg, then the heat absorbed by water is 2.1×105 J, and the efficiency of gas stove to boil water is 50%.

8. As shown in the picture, in picture A, add a few drops of alcohol into the box, then close the lid tightly, then press the button of the spark generator, and you will see the lid fly out. The working process of the gasoline engine in Figure C (optional "B" or "C") is consistent with the energy conversion in this process. If the efficiency of the gasoline engine is 30%, the heat released from complete combustion of 10 kg of gasoline can do 1.38×108 J (the calorific value of gasoline is 4.6×107 J/kg).

9. A certain model of car consumes 10 L of gasoline when driving 100 km on a straight road, and the average resistance is 800 N. It is known that the density of gasoline is 0.7×103 kg/m3, and the calorific value of gasoline is 4.6×107 J. /kg. beg:

(1) The heat released by the complete combustion of 10 L of gasoline;

(2)The efficiency of this car engine.

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Update Time: 2024-09-11

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