Kinetic Theory
Resumen
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.
Objetivos
- 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.
Mapa mental
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Nota de la lección
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Evaluación de la lección
Felicitaciones por completar la lección del Kinetic Theory. Ahora que has explorado el conceptos e ideas clave, es hora de poner a prueba tus conocimientos. Esta sección ofrece una variedad de prácticas Preguntas diseñadas para reforzar su comprensión y ayudarle a evaluar su comprensión del material.
Te encontrarás con una variedad de tipos de preguntas, incluyendo preguntas de opción múltiple, preguntas de respuesta corta y preguntas de ensayo. Cada pregunta está cuidadosamente diseñada para evaluar diferentes aspectos de tu conocimiento y habilidades de pensamiento crítico.
Utiliza esta sección de evaluación como una oportunidad para reforzar tu comprensión del tema e identificar cualquier área en la que puedas necesitar un estudio adicional. No te desanimes por los desafíos que encuentres; en su lugar, míralos como oportunidades para el crecimiento y la mejora.
- 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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