Degree symbol

Note degrees in the Kelvin scale do not have the degree symbol. The units have a capital K, but the noun kelvin has a small letter. 

The degree symbol indicates standard conditions. This means you should use 298 K as the temperature. 

Enthalpies of reaction can also be calculated from individual enthalpies of formation (or heats of formation), AHf, for the reactants and products. Because the temperature, pressure, and state of the substance will cause these enthalpies to vary, it is common to use a standard state convention. For gases, the standard state is 1 atm pressure. For a substance in an aqueous solution, the standard state is 1 molar concentration. And for a pure substance (compound or element), the standard state is the most stable form at 1 atm pressure and 25°C. A degree symbol to the right of the H indicates a standard state, AH°. The standard enthalpy of formation of a substance (AHf) is the change in enthalpy when 1 mol of the substance is formed from its elements when all substances are in their standard states. These values are then tabulated and can be used in determining A//°rxn. 

In the second painting, the candidate has successfully advanced to the next degree, symbolized by a ruined classical temple with treasure strewn on the floor. Her right hand holds a sword which has just severed the satanic serpents head, while her left hand is clasped to her breast. 

A degree symbol (°) signifies less than the smallest unit of measurement shown for that substance (for example, less than 1 kilogram). 

Rule 4 Use °C with a space after the number, but no space between the degree symbol and the capital C. For K (kelvin), include a space between the number and the K do not use the degree symbol with kelvin. 

Property values in the standard state are denoted by the degree symbol (°). For example, C°P is the standard-state heat capacity. Since the standard state for gases is the ideal-gas state, C% for gases is identical with Cj , and the data of Table 4.1 apply to the standard state for gases. All conditions for a standard state are fixed except temperature, which is always the temperature of the system. Standard-state properties are therefore functions of temperature only. 

Use °C with a space after a number, but no space between the degree symbol and the capital C 15 °C. 

Chapter 11 Numbers, Mathematics,and Units of Measure >- 227 >- Do not use the degree symbol with kelvin 115 K. 

Abbreviations mp, melting point bp, boiling point lit., literature value and dec, decomposition. A full space is used between the number and the unit °C the degree symbol is closed up to the C. A superscript number after lit. denotes the number of the reference. 

Spacing, hyphens, and italics. When a unit symbol is given after a number, a space is always left between the number and the symbol with the exception of cases where the symbol appears in the superscript position, such as degree, minute, and second of plane angles. The symbol for degree Celsius may be written either with or without a space before the degree symbol. For example,... 

Now we have two functions that can be used to predict spontaneity the entropy of the universe, which applies to all processes and free energy, which can be used for processes carried out at constant temperature and pressure. Since so many chemical reactions occur under the latter conditions, the free The superscript degree symbol (°) in- energy function is more useful to chemists. 

Heats of reaction at any temperature can be calculated from heat-capacity data if the value for one temperature is known the tabulation of data can therefore be reduced to the compilation of standard heats of formation at a single temperature. The usual choice for tlris temperature is 298.15 K or 25°C. The standard heat of fomration of a compound at tlris temperature is represented by the symbol AHJ. The degree symbol indicates tliat it is the standard value, subscript / shows that it is a heat of fomration, and the 298 is the approximate absolute temperature in kelvins. Tables of these values for common substances may be found in standard handbooks, but the most extensive compilations available are in specialized reference worlai. An abridged list of values is given in Table C.4 of App. C. 

Reaction enthalpy when reactants in their standard states form products in their standard states Degree symbol, °, is added to the reaction enthalpy. 

Enthalpy (H) is defined as the heat content of a substance at constant pressure. We cannot know absolute values of H, only differences in the enthalpies of substances. The enthalpy of formation, AHf of a substance at 25°C (298.15 K) and 1 bar pressure is its heat of formation from the elements in their most stable forms at that temperature and pressure. Here, and generally, the superscript degree symbol to the right of the state function denotes that the function is for 1 bar pressure. AHf for the elements in their most stable forms is taken as zero by definition at any temperature and 1 bar pressure. For example, AH° = 0 for rhombic sulfur, the most stable form of sulfur at 1 bar and 25°C. Monoclinic sulfur, with AHf = 0.071 kcal/mol at 1 bar and 25°C is unstable relative to the rhombic form. 

The divisions of the Fahrenheit and Celsius scales are called degrees, but the divisions of the Kelvin scale are called kelvins (K). The kelvin is the SI rmit of temperature. Note that the degree symbol is not used with temperatures expressed in kelvins. For example, absolute zero is written as 0 K. On the Celsius scale, the temperature reading for absolute zero is —273.15°C, usually rounded to —273°C. A Celsius degree and a kelvin are the same size, so by shifting the Celsius scale up 273°, it will coincide with the Kelvin scale. 

If additional significant figures are needed, 273.15 can be used in place of 273. The standard temperature for gases is 0°C, which is 273 K, a benchmark temperature used when comparing volumes of gases. No degree symbol is used with Kelvin temperatures. More information about the Kelvin temperature scale appears in the discussion of Charles law. 

Degree symbol, 143, 163, 165 Derivative works and copyright, 345, 347 Descriptors, See Chemical descriptors Determinants, 150-152 Deuterium, 258, 259 Dictionaries, desk references of ACS editorial staff, 67, 75 Different from in comparisons, 10 Diffraction lines, crystallographic notation, 260-261... 

Note that in expressing temperature in Celsius units, the designation °C is used. The degree symbol is not used when writing temperature in terms of the Kelvin scale. The unit of temperature on this scale is called a kelvin and is symbolized by the letter K. 

A degree symbol on a thermodynamic function, for example, ATT, indicates that the corresponding process has been carried out under standard conditions. The standard state for a substance is a precisely defined reference state. Because thermodynamic functions often depend on the concentrations (or pressures) of the substances involved, we must use a common reference state to properly compare the thermodynamic properties of two substances. This is especially important because, for most thermodynamic properties, we can measure only changes in the property. For example, we have no method for determining absolute values of enthalpy. We can measure enthalpy changes AH values) only by performing heat-flow experiments. 

The superscript degree symbol (°) indicates all substances are in their standard states. 

You probably use the Fahrenheit scale to measure temperatures, but most scientists and chemists use either the Celsius CC) or Kelvin (TQ temperature scale. (There s no degree symbol associated with K.) Figure 2-4 compares the three temperature scales using the freezing point and boiling point of water as reference points. 

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