"Specific Heat Capacity" Internal Energy PPT (Calculation of Heat in Lesson 2)

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"Specific Heat Capacity" Internal Energy PPT (Calculation of Heat in Lesson 2)

Part One: Knowledge Management

Conditions for heat transfer: If there is a temperature difference between objects or between different parts of the same object, heat transfer will occur and will continue until the temperatures are the same.

Formula: Endothermic formula: Q absorption = cm (t-t0).

Heat release formula: Q release = cm (t0-t).

Comprehensive: Q=______.

Explanation: c is the specific heat capacity of the substance, m is the mass of the object, t0 is the initial temperature, t is the final temperature, and Δt is the change in temperature.

Note: (1) When using formula calculations, the units of each physical quantity must be unified.

(2) During the heat transfer process, if heat loss is not included, Q suction = Q discharge.

Specific heat capacity PPT, part 2 content: classification and exploration

Type one Calculation of heat

[2017•Tianjin Baodi Monthly Examination]A household electric water heater contains 80 g of water. After the heating function is turned on, the temperature of the water increases from 20 ℃ to 60 ℃. How much heat does the water need to absorb? [cwater=4.2×103J/(kg·℃)]

Solution: Heat absorbed by water:

Q suction=cmΔt

＝4.2×103 J/(kg·℃)×80×10-3 kg×60 ℃

=20 160J.

[Method Summary] During the problem solving process, pay attention to the difference between the temperature rise (Δt) and the rise to (end temperature). The endothermic formula Q absorption = cmΔt must be used skillfully, and pay attention to the unity of the units during the calculation process.

Type 2: Calculation of temperature change or mass

[2016•Hunan Yueyang Monthly Examination]Under 1 standard atmospheric pressure, water with a mass of 30 kg and an initial temperature of 60 °C absorbs 8.82×106 J of heat. How much °C can the water temperature increase?

Solution: From Q absorption=cmΔt, we get,

Δt=Q suction cm=8.82×106 J4.2×103 J/kg•℃×30 kg=70 ℃.

The final temperature of water t = t0 + Δt = 60 ℃ + 70 ℃ = 130 ℃. Under 1 standard atmospheric pressure, the boiling point of water is 100 ℃. The maximum temperature of water is 100 ℃ and will not reach 130 ℃. The rising temperature of water is 100℃-60℃=40℃.

[Method Summary] When answering this question, you must pay attention to the relationship between the boiling point of water and atmospheric pressure: at one standard atmospheric pressure, the boiling point of water is 100°C.

Type 3: Implicit conditions in heat calculation

After 1 kg of water at 20 ℃ absorbs 4.2×105 J of heat, its temperature will be at most several possible temperatures among the four temperatures given below ( )

①80 ℃　②100 ℃　③120 ℃　④130 ℃

A. 1B. 2

C. 3D. 4

[Analysis] According to Q absorption=cmΔt, we can get the temperature at which water should rise:

Δt＝Q suction cm＝4.2×105 J4.2×103 J/kg•℃×1 kg＝100℃.

The maximum final temperature of water: tmax = t0 + Δt = 20 ℃ + 100 ℃ = 120 ℃; because the temperature reaches the boiling point when water boils, it continues to absorb heat but the temperature remains unchanged, so the water absorbs heat and rises from 20 ℃. After the temperature reaches the boiling point, It will no longer rise because the air pressure on the surface of the water is unknown and the boiling point of water is uncertain. Therefore, the final temperature of the water may be 80 ℃, 100 ℃, or 120 ℃, but it cannot be 130 ℃, so C is correct.

[Enlightenment] This question comprehensively examines the application of the endothermic formula and the law of liquid boiling. The key is to know that the air pressure will affect the boiling point of the liquid and that the temperature remains unchanged during the boiling process of water.

[Method Summary] When doing the questions, pay attention to the exploration of implicit conditions. For example, in this question, the boiling point of water does not change during the boiling process, which is the use of implicit conditions.

Specific heat capacity PPT, the third part: in-person evaluation

1. (Corresponding Example 3)[2017•Anhui Four Models]As shown in Figure A, in the experiment of "Comparing the heat absorption capabilities of different substances", two different liquids of the same mass, a and b, were put into Two identical beakers are heated simultaneously with the same electric heater. During the heating process, it can be considered that there is no heat loss. Record the relevant data and draw an image as shown in Figure B. If the specific heat capacity of liquid a is 4.2×103J/(kg·℃), then the specific heat capacity of liquid b is ________.

2. (Corresponding example 1)[2016•Adapted from Yiyang, Hunan Province]When the temperature of water with a mass of 100 kg increases from 20 ℃ to 70 ℃, the heat absorbed is ________J. [cWater=4.2×103 J/(kg·℃)]

3. (Corresponding example 2)[2017•Hunan Chenzhou Midterm]Under 1 standard atmospheric pressure, 20 g of water with an initial temperature of 25°C absorbs 6.72×103 J of heat. What is the final temperature of the water? ?

Specific heat capacity PPT, part 4: layered operation

1. (Corresponding example 1)[2017•Bengbu, Anhui Province]The mass ratio of two substances A and B is 2:5, and the ratio of specific heat capacity is 3:2. When the temperature is raised to the same level, the absorbed The ratio of calories is ( )

A. 5:3 B． 3:5

C. 15:4 D. 4:15

2. (Corresponding Example 2)[2016•Sichuan Guang'an Simulation]Use two identical electric heaters to heat substance A and water with the same mass of 2 kg. The relationship between their temperatures changing with time is as shown in the figure shows, based on this, it is judged that the heat absorbed by substance A in 10 minutes is ( )

A. 5.04×105 J

B． 4.2×105 J

C. 2.52×105 J

D. Insufficient conditions to calculate

3. (Corresponding Example 2)[2017•Shanghai]Two metal blocks with different masses release the same amount of heat and reduce the same temperature, then ( )

A. The specific heat capacity of a metal block with a large mass must be large

B． The specific heat capacity of a metal block with a large mass must be small

C. A block of metal with a large mass may have a larger specific heat capacity

D. Two metal blocks may have the same specific heat capacity

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Update Time: 2024-10-04

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