Energy can be transfer via conduction, radiation, convection, or even advection. I like using thermal diffusivity to estimate the rate at which an thermal system approaches steady state.
Heat capacity is the ability of a material to store heat, higher the heat capacity higher the amount to heat stored by the material. Heat transfer usually varies inversely with heat capacity, i.
Thermal diffusivity is the ratio of thermal conductivity to the heat capacity, it says how fast or slow heat is transferred inside a material. Usually thermal diffusivity is directly proportional to the heat transfer rate, since heat capacity appears on the denominator, heat transfer is inversely proportional to the heat capacity. I don't think that the heat capacity and thermal conductivity of a material that closely related. Think about systems rather than materials for a moment.
If you take a lump of material and stick it in a thermos, then the heat capacity stays the same, but the thermal conductivity will plummet. By varying how good the thermos is, you can get a wide range of thermal conductivities. Heat capacity is about storing thermal energy, and thermal conductivity is about moving thermal energy.
As the thermos example shows, those two things needn't be closely related. You can come up with an approximate kinetic formula for thermal conductivity of a material see, for example, Ziman's Electrons and Phonons: The theory of Transport Phenomena in Solids :.
So, all things being equal, larger specific heat means a larger thermal conductivity. Heat, a measure of thermal energy, can be transferred from one point to another. Heat flows from the point of higher temperature to one of lower temperature. Heat transfer takes place in 3 main ways: conduction, convection and radiation. The process of conduction in thermal dynamics is dependent on the factors such as heat transfer coefficient of the material, area, thickness through which the heat is transferred and the change in temperature.
An analogy that could work is an electric circuit that has a battery, a capacitor and a resistor. The higher the capacity which depends on surface area and other factors the more charge it can store, and, the more time it requires for it fully charge.
The resistor affects restricts the flow rate of electric charge The opposite of coefficient of heat transfer. Although the mass of the pan is twice that of the water, the specific heat of water is over four times greater than that of aluminum. Therefore, it takes a bit more than twice the heat to achieve the given temperature change for the water as compared to the aluminum pan.
Truck brakes used to control speed on a downhill run do work, converting gravitational potential energy into increased internal energy higher temperature of the brake material. This conversion prevents the gravitational potential energy from being converted into kinetic energy of the truck. The problem is that the mass of the truck is large compared with that of the brake material absorbing the energy, and the temperature increase may occur too fast for sufficient heat to transfer from the brakes to the environment.
If the brakes are not applied, gravitational potential energy is converted into kinetic energy. When brakes are applied, gravitational potential energy is converted into internal energy of the brake material. This temperature is close to the boiling point of water. If the truck had been traveling for some time, then just before the descent, the brake temperature would likely be higher than the ambient temperature.
The temperature increase in the descent would likely raise the temperature of the brake material above the boiling point of water, so this technique is not practical. However, the same idea underlies the recent hybrid technology of cars, where mechanical energy gravitational potential energy is converted by the brakes into electrical energy battery. Alternatively, the temperature increase could be produced by a blow torch instead of mechanically.
Suppose you pour 0. Assume that the pan is placed on an insulated pad and that a negligible amount of water boils off. What is the temperature when the water and pan reach thermal equilibrium a short time later? The pan is placed on an insulated pad so that little heat transfer occurs with the surroundings.
Originally the pan and water are not in thermal equilibrium: the pan is at a higher temperature than the water. In general, metals like copper, aluminum, gold, and silver are good heat conductors, whereas materials like wood, plastic, and rubber are poor heat conductors.
Figure The average kinetic energy of a particle in the hot body is higher than in the colder body. If two particles collide, energy transfers from the particle with greater kinetic energy to the particle with less kinetic energy. When two bodies are in contact, many particle collisions occur, resulting in a net flux of heat from the higher-temperature body to the lower-temperature body.
Therefore, you will get a more severe burn from boiling water than from hot tap water. Convection is heat transfer by the movement of a fluid. This type of heat transfer happens, for example, in a pot boiling on the stove, or in thunderstorms, where hot air rises up to the base of the clouds. In everyday language, the term fluid is usually taken to mean liquid. However, in physics, fluid means a liquid or a gas.
Fluids move differently than solid material, and even have their own branch of physics, known as fluid dynamics , that studies how they move. As the temperature of fluids increase, they expand and become less dense.
For example, Figure The hotter and thus faster moving gas particles inside the balloon strike the surface with more force than the cooler air outside, causing the balloon to expand. This decrease in density relative to its environment creates buoyancy the tendency to rise. Convection is driven by buoyancy—hot air rises because it is less dense than the surrounding air. Sometimes, we control the temperature of our homes or ourselves by controlling air movement.
Sealing leaks around doors with weather stripping keeps out the cold wind in winter. The house in Figure Ocean currents and large-scale atmospheric circulation transfer energy from one part of the globe to another, and are examples of natural convection. Radiation is a form of heat transfer that occurs when electromagnetic radiation is emitted or absorbed.
Electromagnetic radiation includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays, all of which have different wavelengths and amounts of energy shorter wavelengths have higher frequency and more energy. You can feel the heat transfer from a fire and from the sun. Similarly, you can sometimes tell that the oven is hot without touching its door or looking inside—it may just warm you as you walk by. Another example is thermal radiation from the human body; people are constantly emitting infrared radiation, which is not visible to the human eye, but is felt as heat.
The space between Earth and the sun is largely empty, without any possibility of heat transfer by convection or conduction. Instead, heat is transferred by radiation, and Earth is warmed as it absorbs electromagnetic radiation emitted by the sun. All objects absorb and emit electromagnetic radiation see Figure The rate of heat transfer by radiation depends mainly on the color of the object. Black is the most effective absorber and radiator, and white is the least effective.
People living in hot climates generally avoid wearing black clothing, for instance. Similarly, black asphalt in a parking lot will be hotter than adjacent patches of grass on a summer day, because black absorbs better than green. The reverse is also true—black radiates better than green. Bomb calorimeters require calibration to determine the heat capacity of the calorimeter and ensure accurate results. The calibration is accomplished using a reaction with a known q, such as a measured quantity of benzoic acid ignited by a spark from a nickel fuse wire that is weighed before and after the reaction.
The temperature change produced by the known reaction is used to determine the heat capacity of the calorimeter. The calibration is generally performed each time before the calorimeter is used to gather research data. The final temperature is Use these data to determine the specific heat of the metal. Use this result to identify the metal. Assuming perfect heat transfer, the heat given off by metal is the negative of the heat taken in by water, or:.
Noting that since the metal was submerged in boiling water, its initial temperature was Our experimental specific heat is closest to the value for copper 0. Privacy Policy. Skip to main content. Heat and Heat Transfer. Search for:. Specific Heat. Heat Capacity The heat capacity measures the amount of heat necessary to raise the temperature of an object or system by one degree Celsius.
Learning Objectives Explain the enthalpy in a system with constant volume and pressure. It is measured in joules per Kelvin and given by. The heat capacity is an extensive property, scaling with the size of the system. The heat capacity of most systems is not constant though it can often be treated as such.
It depends on the temperature, pressure, and volume of the system under consideration. Specific Heat The specific heat is an intensive property that describes how much heat must be added to a particular substance to raise its temperature.
Learning Objectives Summarize the quantitative relationship between heat transfer and temperature change. Key Takeaways Key Points Unlike the total heat capacity, the specific heat capacity is independent of mass or volume. It describes how much heat must be added to a unit of mass of a given substance to raise its temperature by one degree Celsius. Values of specific heat are dependent on the properties and phase of a given substance. Since they cannot be calculated easily, they are empirically measured and available for reference in tables.
Key Terms specific heat capacity : The amount of heat that must be added or removed from a unit mass of a substance to change its temperature by one degree Celsius. It is an intensive property. Calorimetry Calorimetry is the measurement of the heat of chemical reactions or physical changes. Learning Objectives Analyze the relationship between the gas constant for an ideal gas yield and volume. Key Takeaways Key Points A calorimeter is used to measure the heat generated or absorbed by a physical change or chemical reaction.
The science of measuring these changes is known as calorimetry. In order to do calorimetry, it is crucial to know the specific heats of the substances being measured. Calorimetry can be performed under constant volume or constant pressure.
The type of calculation done depends on the conditions of the experiment. Key Terms constant-pressure calorimeter : An instrument used to measure the heat generated during changes that do not involve changes in pressure.
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