Chemistry
Specific Heat
Specific heat is the amount of heat energy required to raise the temperature of a substance by a certain amount. It is a physical property that varies for different materials and is measured in joules per gram degree Celsius (J/g°C) or calories per gram degree Celsius (cal/g°C). Specific heat is important in understanding how substances respond to changes in temperature.
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8 Key excerpts on "Specific Heat"
eBook - PDF- T Ferreira(Author)
- 2013(Publication Date)
- Future Managers(Publisher)
5 CHAPTER Heat 5.1 Heat and temperature 5.1.1 Heat Heat is associated with the kinetic energy of molecules. It could therefore be defined as: It could also be said that heat is the amount of energy contained in a body . Since heat is a form of energy, it is often converted into useful work. Heat can be used to convert water into steam. The heat energy stored in the steam can then be used to drive steam engines or steam turbines. 5.1.2 Temperature Temperature refers to how hot or how cold a body is. Our sense of temperature, such as touching an object, is unreliable. It is therefore necessary to make use of instruments such as thermometers and pyrometers, to obtain accurate and objective measurements. 5.2 Specific Heat capacity Different materials of the same mass require different amounts of heat energy to raise their temperatures by the same amount. For example, 1 kg of water requires approximately 4 190 J of heat energy to raise its temperature by 1 °C, as opposed to 385 J required by 1 kg of copper. 5.2.1 Heat capacity It is clear that water has the capacity to absorb almost 11 times the amount of heat energy that copper can for the same rise in temperature. D Definition 5.1 Heat Heat is a form of energy. D Definition 5.2 Temperature Temperature is an indication of the degree of hotness or coldness of a body. D Definition 5.3 Specific Heat capacity Specific Heat capacity is the amount of heat energy required to raise the temperature of 1 kg of a substance 1 °C. Chapter 5 • Heat 80 The amount of heat energy which a substance gains or loses is proportional to: • the mass of the substance, • the Specific Heat capacity of the substance (i.e. the type of material), and • the change in temperature of the substance. Thus Q = mc 3 t joules ....................................................................................................
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 1 Heat Capacity Heat capacity (usually denoted by a capital C , often with subscripts) is the measurable physical quantity that characterizes the amount of heat required to change a body's temperature by a given amount. In the International System of Units, heat capacity is expressed in units of joules per kelvin. Derived quantities include the molar heat capacity , which is the heat capacity per mole of a pure substance. Similarly, Specific Heat capacity (also called more properly mass-Specific Heat capacity or more loosely Specific Heat), is the heat capacity per unit mass of a body. These quantities are intensive quantities. That is, they are not dependent on amount of material, but directly reflect the type of material, as well as the physical conditions of heating. Temperature reflects the average total kinetic energy of particles in matter. Heat is transfer of thermal energy; it flows from regions of high temperature to regions of low temperature. Thermal energy is stored as kinetic energy and, in molecules and solids, also as potential energy in the modes of vibration or phonons. These represent degrees of freedom of movement for atoms. These degrees of freedom, and sometimes others, contribute to the heat capacity of a thermodynamic system. As the temperature approaches absolute zero, the Specific Heat capacity of a system also approaches zero. Quantum theory can be used to quantitatively predict Specific Heat capacities in simple systems. Background Before the development of modern thermodynamics, it was thought that heat was a fluid, the so-called caloric . Bodies were capable of holding a certain amount of this fluid, hence the term heat capacity , named and first investigated by Joseph Black in the 1750s. Today one instead discusses the internal energy of a system. This is made up of its microscopic kinetic and potential energy.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 3 Heat Capacity Heat capacity (usually denoted by a capital C , often with subscripts) is the measurable physical quantity that characterizes the amount of heat required to change a body's temperature by a given amount. In the International System of Units, heat capacity is expressed in units of joules per kelvin. Derived quantities include the molar heat capacity , which is the heat capacity per mole of a pure substance. Similarly, Specific Heat capacity (also called more properly mass-Specific Heat capacity or more loosely Specific Heat), is the heat capacity per unit mass of a body. These quantities are intensive quantities. That is, they are not dependent on amount of material, but directly reflect the type of material, as well as the physical conditions of heating. Temperature reflects the average total kinetic energy of particles in matter. Heat is transfer of thermal energy; it flows from regions of high temperature to regions of low temperature. Thermal energy is stored as kinetic energy and, in molecules and solids, also as potential energy in the modes of vibration or phonons. These represent degrees of freedom of movement for atoms. These degrees of freedom, and sometimes others, contribute to the heat capacity of a thermodynamic system. As the temperature approaches absolute zero, the Specific Heat capacity of a system also approaches zero. Quantum theory can be used to quantitatively predict Specific Heat capacities in simple systems. Background Before the development of modern thermodynamics, it was thought that heat was a fluid, the so-called caloric . Bodies were capable of holding a certain amount of this fluid, hence the term heat capacity , named and first investigated by Joseph Black in the 1750s. Today one instead discusses the internal energy of a system. This is made up of its microscopic kinetic and potential energy.
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
The average kinetic energy of a molecule K ave is proportional to the absolute temperature. Therefore, the change in internal energy of a system is typically proportional to the change in temperature and to the number of molecules, N. Mathematically, ΔU ∝ ΔK total = NK ave ∝ NΔT The dependence on the substance results in large part from the different masses of atoms and molecules. We are considering its heat capacity in terms of its mass, but as we will see in the next chapter, in some cases, heat capacities per molecule are similar for different substances. The dependence on substance and phase also results from differences in the potential energy associated with interactions between atoms and molecules. Heat Transfer and Temperature Change A practical approximation for the relationship between heat transfer and temperature change is: (1.5) Q = mcΔT , where Q is the symbol for heat transfer (“quantity of heat”), m is the mass of the substance, and ΔT is the change in temperature. The symbol c stands for the Specific Heat (also called “Specific Heat capacity”) and depends on the material and phase. The Specific Heat is numerically equal to the amount of heat necessary to change the temperature of 1.00 kg of mass by 1.00 °C . The SI unit for Specific Heat is J/(kg × K) or J/(kg × °C) . (Recall that the temperature change ΔT is the same in units of kelvin and degrees Celsius.) Values of Specific Heat must generally be measured, because there is no simple way to calculate them precisely. Table 1.3 lists representative values of Specific Heat for various substances. We see from this table that the Specific Heat of water is five times that of glass and 10 times that of iron, which means that it takes five times as much heat to raise the temperature of water a given amount as for glass, and 10 times as much as for iron. In fact, water has one of the largest Specific Heats of any material, which is important for sustaining life on Earth.
- Donald Askeland, Wendelin Wright, Donald Askeland(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
At absolute zero, the atoms in a material have a minimum energy. When heat is supplied, the atoms gain thermal energy and vibrate at a particular amplitude and frequency. The vibration of each atom is transferred to the surrounding atoms and produces an elastic wave called a phonon. The energy of the phonon E can be expressed in terms of the wavelength where h is Planck’s constant and c is the speed of light or frequency , just as in Equation 21-1: E 5 hc 5 h (22-1) The energy required to change the temperature of the material one degree is the heat capacity or Specific Heat. The heat capacity is the energy required to raise the temperature of one mole of a material by one degree. The Specific Heat is defined as the energy needed to increase the temperature of one gram of a material by 1°C. The heat capacity can be expressed either at constant pressure, C p , or at a constant volume, C ν . At high temperatures, the heat capacity for a given volume of material approaches C p 5 3R . 6 cal mol ? K (22-2) where R is the gas constant (1.987 calymol); however, as shown in Figure 22-1, heat capacity is not a constant. The heat capacity of metals approaches 6 cal mol ? K near room temperature, but this value is not reached in ceramics until near 1000 K. The relationship between Specific Heat and heat capacity is Specific Heat 5 C p 5 heat capacity atomic weight (22-3) mol ˙ K mol ˙ K Figure 22-1 Heat capacity as a function of temperature for metals and ceramics. Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
eBook - PDF- Vern Ostdiek, Donald Bord(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
In this section, we describe how the temperature of the substance is changed as a result. To simplify matters, we assume that no phase transitions take place. We might state the topic now under consideration in the form of a question: to increase the temperature of a substance by some amount DT, what quantity of heat Q must be transferred to it? (We could just as well ask how much work Q Q must be done on it.) The amount of heat needed is proportional to the temperature increase. It takes twice as much heat to raise the temperature 208C as it does to raise it 108C. So, Q ~ DT The amount of heat needed also depends on the quantity (mass) of the substance to which the heat is transferred. For a given increase in tem- perature, 2 kilograms of water will require twice as much heat transfer as 1 kilogram. So, Q ~ m The required heat transfer also depends on the substance. It takes more heat to raise the temperature of water 18C than it does to raise the temperature of an equal mass of iron 18C. As with thermal expansion (Section 5.2), a character- r r istic value can be assigned to each substance indicating the relative amount of heat needed to raise its temperature. This number, called the Specific Heat capac- ity C, is determined experimentally for each substance. The larger the Specific Heat capacity of a substance, the greater the amount of heat transfer needed to raise its temperature by a given amount. Thus, Q ~ C We can combine the three proportionalities into the following equation: Q 5 C m DT The amount of heat required equals the Specific Heat capacity of the substance times the mass of the substance times the temperature increase. The SI unit of Specific Heat capacity is the joule per kilogram-degree Celsius (J/kg-8C). If the Specific Heat capacity of a substance is 1,000 J/kg-8C, then it takes 1,000 joules of energy to raise the temperature of 1 kilogram of that substance 18C.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
A greater amount of heat is also required to raise the temperature of a greater mass of material. Similar comments apply when the temperature is lowered, except that heat must be removed. For limited temperature ranges, experiment shows that the heat Q is directly proportional to the change in temperature DT and to the mass m. These two propor- tionalities are expressed below in Equation 12.4, with the help of a proportionality constant c that is referred to as the Specific Heat capacity of the material. Heat Supplied or Removed in Changing the Temperature of a Substance The heat Q that must be supplied or removed to change the temperature of a substance of mass m by DT degrees is Q 5 cm DT (12.4) where c is the Specific Heat capacity of the substance. Common Unit for Specific Heat Capacity: J/(kg ? C°) Heat flow Heat flow (a) (b) Figure 12.22 Heat is energy in transit from hot to cold. (a) Heat flows from the hotter coffee cup to the colder hand. (b) Heat flows from the warmer hand to the colder glass of ice water. 12.7 | Heat and Temperature Change: Specific Heat Capacity 329 Solving Equation 12.4 for the Specific Heat capacity shows that c 5 Q/(m DT), so the unit for Specific Heat capacity is J/(kg ? C8). Table 12.2 reveals that the value of the Specific Heat capacity depends on the nature of the material. Examples 9 and 10 illustrate the use of Equation 12.4. EXAMPLE 9 | A Hot Jogger In a half hour, a 65-kg jogger can generate 8.0 3 10 5 J of heat. This heat is removed from the jogger’s body by a variety of means, including the body’s own temperature-regulating mechanisms. If the heat were not removed, how much would the jogger’s body temperature increase? Reasoning The increase in body temperature depends on the amount of heat Q generated by the jogger, her mass m, and the Specific Heat capacity c of the human body. Since numerical values are known for these three variables, we can determine the potential rise in temperature by using Equation 12.4.
eBook - PDF- Richard L. Myers(Author)
- 2005(Publication Date)
- Greenwood(Publisher)
Heat transfer may cause a phase change, and no temperature change occurs as long as two phases are present. In this situation, heat is referred to as latent heat. The relationship between heat and phase changes will be examined in the next section. The relationship between heat trans- fer, Q, and the change in temperature of a substance depend s on the Specific Heat 86 Heat capacity of the substance. The Specific Heat capacity of a substance is a measure of the amount of heat necessary to raise the tem- perature of 1 g of the substance by 1°C. The Specific Heats of several common substances are listed in Table 6.1. Table 6.1 demon- strates that the Specific Heat of a substance depends on its phase. The Specific Heat of liquid water is approximately twice that of ice and steam. Water has one of the highest Specific Heats compared to other liquids. The high Specific Heat capacity of liquid water is directly related to its chemical structure and the presence of hydrogen bonds. The high Specific Heat of water explains why coastal environments have more moderate weather than areas at similar latitudes located inland. Water's high Specific Heat capacity means coastal regions will not experience drastic temperature changes as compared to inland regions. The relationship between heat, Specific Heat capacity, and temperature change of a substance is given by the equation Q = mcAT. In this equation, Q is the amount of thermal Table 6.1 Specific Heat Capacity of Some Common Substances Substance Steel Wood Ice Liquid water Steam Air Alcohol Specific Heat J/g=°C 0.45 1.7 2.1 4.2 2.0 1.0 2.5 energy (often Q is referred to simply as heat) transferred in joules, m is the mass in grams, c is the Specific Heat capacity of the sub- stance, and AT is the change in temperature. The temperature change is equal to the final temperature minus the initial temperature. As an application of this equation, consider what happens when heating a pot of water on the stove.
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