Celsius scale

Temperature. Temperature maybe measured on an absolute or relative scale. The two most common relative scales are the Celsius and the Fahrenheit scales. The Celsius scale is defined as 0°C at the freezing point (triple point) of water and 100°C at the boihng point. The Fahrenheit scale is arbitrarily defined by assigning it a temperature of 32 degrees at the freezing point of water and 212°F at the boihng point of water (see Temperature measurements). 

The absolute temperature scale that corresponds to the Celsius scale is the Kelvin scale for the Fahrenheit scale, the absolute scale is called the Rankine scale. The Celsius scale reads 0 when the Kelvin scale reads 273 the Fahrenheit scale reads 0 when the Rankine scale reads 460. These relationships are shown in Figure 1. 

The volume of a gas would theoretically be zero at a temperature of approximately -273°C or -460°F. Tliis temperature, wliich lias become known as absolute zero, is tlie basis for tlie definition of two absolute temperature scales, tlie Kelvin (K) and Rankine (°R) scales. The former is defined by shifting tlie Celsius scale by 273-Celsius degrees so that 0 K is equal to -273°C. Equation (4.2.3) shows tliis relation. 

The general temperature scale now in use is the Celsius scale, based nominally on the melting point of ice at 0°C and the hoiling point of water at atmospheric pressure at 100°C. (By strict definition, the triple point of ice is 0.01°C at a pressure of 6.1 mhar.) On the Celsius scale, absolute zero is -2 73.15°C. 

In the study of refrigeration, the Kelvin or absolute temperature scale is also used. This starts at absolute zero and has the same degree intervals as the Celsius scale, so that ice melts at + 2 73.16 K and water at atmospheric pressure boils at + 373.15 K. 

The Fahreuheit and Celsius temperature scales. The distance between the freezing and boiling points of water is 180° on the Fahrenheit scale and 100° on the Celsius scale. Thus the Celsius degree is 9/5 as large as the Fahrenheit degree, as is evident from the magnified section of the thermometer above. 

Two scales used in die measuring of temperatures are Fahrenheit (F) and Celsius (C) (also known as centigrade). On the Fahrenheit scale, die freezing point of water is 32° F and die boiling point of water is 212° F. On die Celsius scale, 0° C is the freezing point of water and 100° C is die boiling point of water. 

A note on good practice Note that the volume (or the pressure) doubles when the temperature is doubled on the absolute (Kelvin) scale, not when it is doubled on the Celsius scale. An increase from 20°C to 40°C corresponds to an increase from 293 K to 313 K, an increase of only 7%. 

The Kelvin temperature scale is defined to have the freezing point of pure water at 273.15 K and the normal boiling point of pure water at 373.15 K. The unit of the Kelvin temperature scale is the kelvin. (We do not use degrees with Kelvin.) Thus, its temperatures are essentially 273° higher than the same temperatures on the Celsius scale. To convert from Celsius to Kelvin, merely add 273° to the Celsius temperature. To convert in the opposite direction, subtract 273° from the Kelvin temperature to get the Celsius equivalent. (See Fig. 2-2.)... 

Kelvin temperature scale a temperature scale with its 0 at the lowest theoretically possible temperature (0 K = - 273 °C) and with temperature differences the same as those on the Celsius scale. 

To convert the temperature from Fahrenheit scale to Celsius scale, the following expression may be used ... 

We in the United States are used to thinking of temperature in Fahrenheit, but most of the rest of the world measures temperature in Celsius. On the Celsius scale water freezes at 0°C and boils at 100°C. Here are the equations needed to convert from Fahrenheit to Celsius and vice versa ... 

The Celsius scale is a relative scale. It was designed so that water s boiling point is at lOO C and water s melting point is at 0 C. The Kelvin scale, on the other hand, is an absolute scale. It was designed so that 0 K is the temperature at which a substance possesses no kinetic energy. The relationship between the Kelvin and Celsius scales is shown in Figure 5.2, and by the following equation. 

Figure 3.10 Temperature scales Celsius and Kelvin (absolute). On the Celsius scale, absolute zero is -273 °C. The temperature at which water boils is, therefore, 373 °K. Most life on earth exists only between 277 and 293 °K.

A temperature measured on an absolute temperature scale (i.e., a scale in which zero degrees is equivalent to absolute zero). In the Kelvin scale, the degree unit is the kelvin, abbreviated as K it does not have the superscript o used to indicate degree as on the Celsius scale. K has the same magnitude as degree Celsius (°C). 

Because the volume of a gas decreases with falling temperature, scientists realized that a natural zero-point for temperature could be defined as the temperature at which the volume of a gas theoretically becomes zero. At a temperature of absolute zero, the volume of an ideal gas would be zero. The absolute temperature scale was devised by the English physicist Kelvin, so temperatures on this scale are called Kelvin (K) temperatures. The relationship of the Kelvin scale to the common Celsius scale must be memorized by every chemistry student ... 

Knowledge of the numerical value of the entity represented by Eq. (9.1) allows one to make up cells that give the potential of an electrode "on the absolute scale, just as the Celsius scale was later shown to be expressed on the absolute or Kelvin scale of temperatures, in which there is a rationally based zero at -273 °C. Thus, to find the absolute value, VM>abs of an electrode potential expressed on the standard hydrogen scale, one writes... 

Three different scales are in common use for measurements of temperature the Celsius scale (expressed in degrees Celsius, or °C), the Fahrenheit scale (expressed in degrees Fahrenheit, or °F), and the Kelvin scale (expressed in kelvins, or K). The Fahrenheit scale is commonly used in daily life and in engineering work. The Celsius scale is used in scientific work and is coming into common usage in daily life in English-speaking countries. The Kelvin scale (also called the absolute scale) is the SI choice for temperature measurements, and it is widely used in scientific work. 

The Imaginary scale and the Celsius scale both have the same zero point (the freezing point of water), but they differ in the size of their units. The readings on the Celsius scale will always be just 100/180 = 5/9 of the readings on the Imaginary scale, so the conversion formula from one to the other is... 

The units of the Kelvin scale are the same size as those of the Celsius scale, but the zero point of the Kelvin scale is 273.2 units lower than that of the Celsius scale. Therefore, K = °C + 273.2 = 5/9(°F - 32) + 273.2. 

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