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Ch 19: Work, Heat, and the First Law of Thermodynamics
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoKnight Calc 5th EditionCh 19: Work, Heat, and the First Law of ThermodynamicsProblema 24
Capitolo 19, Problema 24

A 65 cm3 block of iron is removed from an 800°C furnace and immediately dropped into 200 mL of 20°C water. What fraction of the water boils away?

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1
Convert the given volumes into masses. For the iron block, use the density of iron (approximately 7.87 g/cm³) to calculate its mass. For water, use the density of water (1 g/mL) to determine its mass.
Calculate the heat lost by the iron block as it cools from 800°C to 100°C (the boiling point of water). Use the formula for heat transfer: Q = mcΔT, where m is the mass of the iron, c is the specific heat capacity of iron (approximately 0.45 J/g°C), and ΔT is the temperature change.
Determine the heat required to raise the water from 20°C to 100°C using the same heat transfer formula: Q = mcΔT, where c is the specific heat capacity of water (4.18 J/g°C).
Calculate the heat required to boil the water at 100°C using the formula: Q = mL, where L is the latent heat of vaporization of water (2260 J/g).
Compare the heat lost by the iron block to the total heat required to raise the water to 100°C and boil it. The fraction of water that boils away is the ratio of the heat available for vaporization to the heat required for vaporizing the entire mass of water.

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Heat Transfer

Heat transfer is the process by which thermal energy moves from one object to another due to a temperature difference. In this scenario, the hot iron block will transfer heat to the cooler water until thermal equilibrium is reached. Understanding the mechanisms of conduction, convection, and radiation is essential for analyzing how heat moves between the iron and water.
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Overview of Heat Transfer

Specific Heat Capacity

Specific heat capacity is the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius. Each material has a unique specific heat capacity, which influences how much heat it can absorb or release. In this problem, knowing the specific heat capacities of both iron and water is crucial for calculating the temperature change and the resulting heat transfer.
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Specific Heat & Temperature Changes

Phase Change and Latent Heat

Phase change refers to the transition of a substance from one state of matter to another, such as from liquid to gas. During this process, energy is absorbed or released without a change in temperature, known as latent heat. In this question, understanding the latent heat of vaporization for water is vital to determine how much water can boil away as it absorbs heat from the iron block.
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Latent Heat & Phase Changes
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