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. Can. J. Chem. 60, 1872Chem. 60, (1982.A flow microcalorimeter and vibrating tube densimeter were used to obtain apparent molal heat capacities and volumes of aqueous NaHS and NazS from 0.1 to 1.0 mol kg-' and of aqueous H2S from 0.03 to 0.08 mol kg-' at 10,25, and 40°C. Standard state heat capacities and volumes for H2S and HS-were obtained by extrapolation to infinite dilution. Combining these results with 2S°C enthalpy data yields an expression for the temperature dependence of the equilibrium constant for H2S neutralization at pressures near those of steam saturation, H2S + OH-= HS-+ H 2 0 , log K , b = 19.84 + 930.8lT -2.800 In T, with an estimated uncertainty of k0.47 at 300°C. The heat capacity data for bulk aqueous NazS suggest that the relative concentration of SZ-at these molalities is small. Les donntes de capacitt calorifique pour la masse aqueuse de Na2S suggkrent que la concentration relative de S2-est petite a ces molalitts.[ The e n t h a l~~ of the ionization reaction at 25°C is and hydrometallurgical procedures for treating (49 5, and has been wed in the van't HOff sulfide ores. Low temperature measurements have equation to extrapolate K1 to high temperatures been made by many workers using a variety of (1). The standard volume and heat capacity of techniques (1) and the values for K, near 2 5 0~ are ionization are required in such an extrapolation to well established. Experiments above 100°C are account for the effects of pressure and7 more difficult, largely because aqueous sulfide poisons important7 changes in the e n t h a l~~ of reaction with the platinum electrodes commonly used to deter-temperature7 respectively. As yet7 no accurate mine ionization constants in high temperature values for these properties have been reported. We water. Ellis and co-workers (2) obtained data for have now measured apparent molal heat capacities K l , up to 276°C using a spectrophotometric meth-and for NaHS and at od, but noted that the results might be in emor since peratures of 10°C7 25"C, and 40°C. he results ~i e l d their technique did not permit in situ p~ measure-both infinite dilution and excess partial molal heat capacities and volumes for these important species 'Visiting scientist at the Oil Sands Research Department, which can then be combined with existing low

. Can. J. Chem. 61, 2509Chem. 61, (1983. A flow microcalorimeter and vibrating tubc densimeter were used at 25°C to obtain apparcnt molar heat capacitics and volumes of aqueous NaHCO1, KHCO,. NaHSO,, and KHSO, from 0. I to I .O mol kg-'. aqueous CO, from 0.01 to 0.10 mol kg-' and aqueous SO, from 0.045 to 2.0 mol kg-'. The contribution of "chemical relaxation" (changes in cquilibrium state and enthalpy due to change in temperature) to thc experimental heat capacitics of aqucous SO, required special attention, leading to the derivation of a new equation for calculating this cffcct. Standard statc valucs for thc heat capacities and volurnes of aqueous CO,, SOz, HCO,.., and H S O , were obtained from the apparent molar properties by extrapolation to infinite dilution. Combining these rcsults with othcr thcrmodynamic data from the literature gave estimates of log K,", the cquilibrium constant for the first neutralization of CO, and SO?, at high temperatures. The results for CO, reproducc very accuratc literature values to within 0.2 at 200°C. The expression for the reaction SO, t O H S HS0,-, log K l h = 22.771 t 2776.0/T -8.058 log T, is consistent with the sparse and limited experimental data.

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Population growth, urban expansion, and greater prosperity lead to an increased flow of people and goods in cities. Transport systems face difficulties in coping with these escalations in demand, particularly when individual motorized transport becomes dominant. In this context, the urban mobility agenda is not limited to ensuring the provision of adequate access for people and goods, but should also try to reduce the negative impacts generated by transportation systems. Urban transport is facing a radical change as it looks for solutions compatible with sustainable development. This demands coordination of mobility strategies with other public policies, particularly those directed at urban development, housing, social inclusion, the environment, and energy. The challenge is greater in the developing world cities, where motorization is developing fast, public transport networks are weak, and there are significant financial and institutional barriers.