Kinetic Theory
Aperçu
Stand a pan of crushed ice on a hot ring with a thermometer in it and watch the reading. It climbs to zero and then it stops. The ring is still glowing, the ice is visibly turning to water, joules are pouring in at hundreds every second, and the number on the thermometer refuses to move. It stays there for minutes. Only when the last sliver of ice has gone does the reading start to rise again, and later, at one hundred, it stalls a second time and stays stalled while the pan boils dry. Two flat stretches in one heating, and in both of them energy is arriving with nothing to show for it on the scale.
Nothing has gone missing. This lesson shows you where those joules went, and it hands you a way of reading any temperature against time graph as a story about particles: how far apart they are, how fast they move, and how tightly they are held to each other. You will define specific heat capacity and the two specific latent heats, put numbers into the three equations that go with them, learn to tell instantly which equation belongs to which part of a graph, and finish by cooling molten stearic acid in a test tube and watching the same flat stretch appear in reverse.
Objectifs
- Kinetic theory can be used to explain the different states of matter and their properties. The particles in solids, liquids and gases have different amounts of energy. Students should be able to recognise, use and compare simple diagrams to represent key features of solids, liquids and gases.
- The specific heat capacity of a substance is the amount of energy required to change the temperature of one kilogram of the substance by one degree Celsius. The relationship between energy, E, mass, m, specific heat capacity, c, and temperature change, ∆θ, is: E = m × c ×∆θ
- The specific latent heat of vaporisation of a substance is the amount of energy required to change the state of one kilogram of the substance from a liquid to a vapour with no change in temperature. The relationship between energy, E, mass, m, and specific latent heat of vaporization, LV , is: E = m × LV
- The specific latent heat of fusion of a substance is the amount of energy required to change the state of one kilogram of the substance from a solid to a liquid with no change in temperature. The relationship between energy, E, mass, m, and specific latent heat of fusion, LF , is: E = m × LF
- The melting point of a solid and the boiling point of a liquid are affected by impurities. Required practical: Investigate cooling curves for stearic acid. Throughout Section 3.4, students should be able to explain the shape of the temperature-time graph for a substance that is either cooled or heated through changes in state.
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Évaluation de la leçon
Félicitations, vous avez terminé la leçon sur Kinetic Theory. Maintenant que vous avez exploré le concepts et idées clés, il est temps de mettre vos connaissances à l'épreuve. Cette section propose une variété de pratiques des questions conçues pour renforcer votre compréhension et vous aider à évaluer votre compréhension de la matière.
Vous rencontrerez un mélange de types de questions, y compris des questions à choix multiple, des questions à réponse courte et des questions de rédaction. Chaque question est soigneusement conçue pour évaluer différents aspects de vos connaissances et de vos compétences en pensée critique.
Utilisez cette section d'évaluation comme une occasion de renforcer votre compréhension du sujet et d'identifier les domaines où vous pourriez avoir besoin d'étudier davantage. Ne soyez pas découragé par les défis que vous rencontrez ; considérez-les plutôt comme des opportunités de croissance et d'amélioration.
- Which statement describes the particles in a liquid? A. Held in fixed positions in a regular arrangement B. In contact with one another but free to slide past each other C. Widely separated and moving quickly in random directions D. Widely separated and held in fixed positions Answer: B
- What is the unit of specific heat capacity? A. J B. J/kg C. J/kg/degC D. degC/J Answer: C
- The specific heat capacity of water is 4200 J/kg/degC. How much energy is needed to raise the temperature of 2.0 kg of water from 15 degC to 35 degC? A. 42 000 J B. 84 000 J C. 168 000 J D. 294 000 J Answer: C
- A pure substance is heated steadily and its temperature stays constant for several minutes. Which statement is correct for that period? A. No energy is being transferred to the substance B. The energy transferred is increasing the average speed of the particles C. The energy transferred is separating the particles as the substance changes state D. The energy transferred is being destroyed Answer: C
- The specific latent heat of vaporisation of water is 2.3 x 10^6 J/kg. How much energy is needed to turn 0.050 kg of water at 100 degC into steam at 100 degC? A. 4.6 x 10^4 J B. 1.15 x 10^5 J C. 1.15 x 10^6 J D. 4.6 x 10^7 J Answer: B
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Livres recommandés
Pour aller plus loin, ressources libres
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Section de manuel
Phase Change and Latent Heat
Explain changes in heat during changes of state, and describe latent heats of fusion and vaporization
"Physics: Phase Change and Latent Heat" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/physics/pages/11-3-phase-change-and-latent-heat. Access for free at https://openstax.org/books/physics/pages/1-introduction
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Section de manuel
Temperature Change and Heat Capacity
One of the major effects of heat transfer is temperature change: heating increases the temperature while cooling decreases it. We assume that there is no phase change and that no work is done on or by the system. Experiments show that the transferred heat depends on three factors—the change in tempe
"College Physics: Temperature Change and Heat Capacity" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/14-2-temperature-change-and-heat-capacity. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
Publiées par d'autres organisations sous licence libre, créditées comme elles le demandent. Les liens ouvrent leurs sites.
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