Constants in SI units

For the foreseeable future, you will need to make conversions from other units to SI units, as much of the literature quotes data using imperial, c.g.s. or other systems. You will need to recognize these units and find the conversion factors required. Examples relevant to chemistry are given in Box 9.1. Table 9.4 provides values of some important physical constants in SI units. 

The values of some common physical constants in SI units include ... 

Properties of some metals and alloys Values of important constants in SI units (RT/F) log X at various temperatures Standard chemical potentials... 

By contrast, in SI units, the coulomb (C) is the unit of charge and is defined as an ampere second (A sec). To reconcile this with newtons and meters, the units of F and r, respectively, a proportionality constant that is numerically different from unity and which has definite units is required. For charges under vacuum we write... 

Where ij. is defined as the kinematic viscosity (centistokes), and is a constant with a value of 2,213.8 in USCS units and 353.68 in SI units. An empirical relation for the Fanning friction factor is the Colebrook-White equation ... 

In this book, we will express our thermodynamic quantities in SI units as much as possible. Thus, length will be expressed in meters (m), mass in kilograms (kg), time in seconds (s), temperature in Kelvins (K), electric current in amperes (A), amount in moles (mol), and luminous intensity in candella (cd). Related units are cubic meters (m3) for volume, Pascals (Pa) for pressure. Joules (J) for energy, and Newtons (N) for force. The gas constant R in SI units has the value of 8.314510 J K l - mol-1, and this is the value we will use almost exclusively in our calculations. 

For diatomic molecules, B0 is the rotational constant to use with equation (10.125), while Be applies to equation (10.124). They are related by Bq = Be 2 - The moment of inertia 70(kg-m2) is related to 50(cm ) through the relationship /0 = h/ 8 x 10 27r22 oc), with h and c expressed in SI units. For polyatomic molecules, /a, /b, and Iq are the moments of inertia to use with Table 10.4 where the rigid rotator approximation is assumed. For diatomic molecules, /0 is used with Table 10.4 to calculate values to which we add the anharmonicity and nonrigid rotator corrections. 

The constant term within the brackets has a value of 172.3005 in SI units (J-K- -mor1). 

In this equation, T is the temperature in kelvins, is Avogadro s number (units of molecules/mol), and R is the gas constant. For energy calculations, we express R in SI units, which gives kinetic energy in joules per molecule. The value of R in SI units is i = 8.314 J mol K ... 

The energy of a dipole in a constant electric field in SI units is given by ... 

Care the odd-looking units of B require us to cite the gas constant R in SI units with prefixes. 

In SI units, T>jk is measured in m2/s. Consistent units in the first expression are ks = 1.38066 x 10-23 J/K is the Boltzmann constant, mjk is the reduced molecular mass (kg), p is the pressure (N/m2), T is temperature (K), and ajk is a reduced collision diameter (m). The second expression in Eq. 3.95 replaces the Boltzmann constant and the molecular mass with the gas constant R = 8.31451 J/g-mol K and the reduced molecular weight Wjk (g/mol), which requires Avogadro s number A. Assuming that Wjk is given in g/mol, the divide by 1000 is required to maintain SI units. The reduced mass and collision diameter are given as... 

In this equation, V2 = d2/dx2 + d2/dy2 + d2/dz2 denotes the Laplacian operator of cartesian second derivatives, p(r) is the charge density in a spherical shell of radius r and infinitesimal thickness dr centered at the particle of interest (see diagram), k is the effective dielectric constant, and e0 is the permittivity of free space (8.854 x 10 12 in SI units). The energy of interaction / , of ions of charge z,c with their surroundings,... 

Laboratory experiments, confirmed by data from large scale operations, have shown that ethane decomposition is a homogeneous first order reaction, the rate constant (s ) being given by the equation in SI units 6 ... 

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