"Studying the Specific Heat Capacity of Substances" Internal Energy and Heat Engine PPT Courseware 4

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"Studying the Specific Heat Capacity of Substances" Internal Energy and Heat Engine PPT Courseware 4

The amount of heat absorbed by a certain substance when it heats up may be related to what factors, and what is the relationship?

Does it take the same amount of heat to boil a full pot of water as it does to boil a half pot?

Not the same amount, a full pot of water requires more calories

Does it take the same amount of heat to boil a kettle of water as it does to make it lukewarm?

Not the same amount. It takes more heat to boil water.

Summary: For the same substance (such as water), the heat absorbed by the water is related to the _________ and _________ of the water.

The more _____ the mass is, the _____________ absorbed;

The more degrees the temperature rises ______, the more ___________ absorbed

1. Specific heat capacity

1. Explore the ability of matter to absorb heat

think about it

Why do sand and seawater rise in temperature differently under the same sunlight conditions? Is it because sand and water are different substances?

Do it

Compare it with different substances!

See if different types of substances absorb heat in the same way.

Experiment preparation

(1) Compared to what? Who to compare with? How to compare?

(2) How to know which substance absorbs more heat?

(3) What data should be recorded?

conduct experiment

1. To study this problem, we must keep _____ and _________ the same and __________ different.

2. Take two ______ beakers to hold two liquids (water and kerosene) in ______, heat them with two electric heaters in _____ to make them rise __________, and observe their __________ length.

Experimental results

Experimental phenomena:

The same mass of water and kerosene rise to the same temperature, and the water takes longer to heat.

Experiment instructions:

Different substances of equal mass need to absorb different amounts of heat to raise the same temperature.

Conclusion: The heat absorbed by an object is not only related to the mass of the object and the change of the temperature of the object, but also related to the type of material.

2. What is specific heat capacity

After scientific measurements, it was found that in general, different substances absorb different amounts of heat when their masses are equal and their temperature rises the same. This property of matter is represented by the physical quantity specific heat capacity.

The ratio of the heat absorbed by a certain mass of a substance when its temperature rises to the product of its mass and the rising temperature is called the specific heat capacity of the substance.

The specific heat capacity is represented by the symbol c, its unit is joules per kilogram, and the symbol is J/(kg · ℃).

Understand specific heat capacity

The specific heat capacity of water is: c water = 4.2×103 J/(kg · ℃)

The specific heat capacity of salad oil is: c oil = 1.97×103 J/(kg·℃)

Try to tell the physical meaning of the specific heat capacity of water:

The heat absorbed or released when the temperature of 1 kg of water increases or decreases by 1°C is 4.2×103 J.

The essence of specific heat capacity

(1) Reflects the ability of a substance to absorb and release heat;

The greater the specific heat capacity, the stronger the ability to absorb or release heat.

(2) The sensitivity of a substance to hot and cold reactions;

The smaller the specific heat capacity, the more sensitive it is to heat and cold.

3. Use the knowledge of specific heat capacity to explain some phenomena

Regardless of the economic cost, let’s talk about whether it is better to use water or oil for heating?

There is a proverb in Xinjiang:

"Wear a fur coat in the morning and eat watermelon around the stove in the afternoon."

Can you make sense of it?

2. Calculation of heat

The heat absorbed by 1kg of water when the temperature rises by 1°C is __________ J.

The heat absorbed by 2kg of water when the temperature rises by 1°C is _________ J.

The heat absorbed by 2kg of water when the temperature rises by 10°C is _________J

Refined formula

Heat absorbed = specific heat capacity × mass × increased temperature

Q suction = cm(t1-t0) Q release = cm(t0-t1)

Example 1. How much heat needs to be absorbed to heat water with a mass of 2kg from 50℃ to boiling at 1 standard atmosphere?

Solution: c=4.2×103J/(kg·℃)

△t=100 ℃-50 ℃=50 ℃

Q suction=cm △t

=4.2×103J/(kg·℃)×2kg×50℃

=4.2×105J

Answer: It needs to absorb 4.2×105J of heat.

Example 2. Boiling water (100°C) with a mass of 2kg has a temperature lowered by 60°C. How much heat does the water release?

Solution: Q put=cm(t0-t)

＝4.2�103J/(kg.℃) ×2kg × 60℃

＝5.04 × 105J

Answer: Water releases 5.04 × 105J heat

practice

1. Regarding specific heat, which of the following statements is correct ( )

A. The specific heat capacity of an object is related to temperature

B. The specific heat capacity of an object is related to the heat absorbed and released by the object

C. The specific heat capacity of an object is a characteristic of the substance itself

D. The greater the mass of an object, the greater its specific heat capacity.

2. Which of the following statements is correct ( )

A. If half of a cup of kerosene is used, its specific heat capacity will be reduced to half of its original value.

B. A substance that absorbs more heat must have a greater specific heat.

C. High-temperature objects must release a lot of heat

D. Water and kerosene of equal mass absorb the same amount of heat. The temperature of kerosene rises greater than that of water.

3. In agricultural production, in order to protect the seedlings from freezing at night, more water should be poured into the rice fields in the evening. This is because water ( )

A.High density B.High specific heat capacity C.High temperature D.High thermal expansion

4. The temperature changes between day and night in coastal areas and southeastern my country are ____, while in desert areas and northwest my country, the temperature changes between day and night are ____. Why?

Answer: This is because when heated and cooled at the same time, that is, when the heat absorption or heat release is the same, the specific heat capacity of water is large and the temperature change is small; the specific heat capacity of sand and gravel is small and the temperature change is large.

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Update Time: 2024-11-23

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